Cellular bio pt 2
The activities of a living cell depend on its membrane's abilities to:
transport raw materials into the cell, transport manufactured products and waste out of the cell, prevent unwanted matter entry into the cell, prevent the escape of essential matter, regulate the movements of ions in and out of the cell
Phospholipid bilayers
form bilyaers in water due to their amphipathic properties (both hydrophilic and hydrophobic properties), they arrange themselves so that the non-polar tail is tucked away from water, and the polar heads are facing water, this layer is very stable as the heads bond with the water and a weak intermolecular interaction in the tails
Emergent properties
Phospholipids will self-organize when put into water to keep their heads wet and their tails dry. Phospholipid molecules can flow past eachother laterally but not vertically
Davson and Danielli
they created a model that proposes phospholipid bilayers are together and coated by proteins on either side (they do not permeate the bilayer), they used freeze-etching/fracturing with a microscope the figure this out
Singer-Nicholson fluid mosaic model
phospholipids form a bilayer and are fluid, peripheral proteins are bound to either the inner or outer surface of the membrane, integral proteins permeate the surface of the membrane, proteins can move laterally across the membrane, membrane is a fluid mosaic of phospholipids
Biochemical techniques
membrane proteins were found to be globular and varied in size, which would be unable to form continuous layers on the periphery of the membrane, these proteins had hydrophobic regions and would embed into the membrane and not layer outside
Fluorescent antibody tagging
red or green fluorescent markers attached to antibodies which would bind to membrane proteins, each with a different colour, they fused together. Within 40 minutes the red and green markers were mixed throughout the membrane of the fused cell.•This showed that membrane proteins are free to move within the membrane rather than being fixed in a peripheral layer.
Proteins (membrane structure)
Integral proteins are permanently embedded (many go through all the way and are polytopic) proteins that only go through one surface are monotopic. Peripheral proteins have temporary association with the membrane. The glycocalyx is a thin sugar layer formed by carbohydrate chains that attaches to proteins to cover a cell, used for adhesion, reception and recognition
Functions of membrane proteins
Transport: Protein channels (facilitated) and protein pumps (active)
Receptors: Peptide-based hormones (insulin, glucagon, etc.)
Anchorage: Cytoskeleton attachments and extracellular matrix
Cell recognition: MHC proteins and antigens They provide an identification label representing cells of different types or species.
Intercellular joinings: Tight junctions and plasmodesmata
Enzymatic activity: Metabolic pathways (e.g. electron transport chain)
Cholesterol
allows membranes to function in a wider range of temperatures by interacting with phospholipid bilayer tails, cholesterol is a steroid, only animals have it
membrane fluidity
phosphate heads act more like a solid, and the tails more like a liquid. Membranes have to be fluid enough for the cell to move and required substances can move across the membrane, but not too much so that it couldn't restrict movement
Fatty acids and membrane fluidity
Since only the heads can bond to water, weak bonds allow proteins and phospholipids to move freely, often fatty acids will be a different composition on the inside layer than on the outside since they are exposed to more drastic temperatures. Unsaturated fatty acids for low temperatures, saturated for high temperatures
membrane fluidity in bacteria
bacteria do not have the ability to maintain a constant internal temperature, so their membranes are more susceptible to temperature changes, Fatty acid desaturates are enzymes that turn saturated fatty acids to unsaturated when temperatures begin to cool
Cholesterol and membrane fluidity
Restricts movement, disrupts regular packing and increases flexibility, reduces permeability to polar molecules and ions, stabilizes membranes at higher temperatures
Cell adhesion molecules
Desmosomes: form sturdy but flexible sheets of cells in organs that tend to stretch such as the heart or stomach, channels can be used to anchor cells together and allow ions to pass through for communication
Plasmodesmata: found within plant cells, tubes connecting the cytoplasm of adjacent cells, allows exchange of materials like water or small solutes
The cell theory
All living organisms are composed of one or more cells.
Cells are the smallest units of life.
All cells come from pre-existing cells.
inductive reasoning
Theories developed from observations are an example of inductive reasoning, using specific observations to form a general conclusion
deductive reasoning
using a general premise to form a specific conclusion
Passive transport
the movement of ions or molecules across a cell membrane from a region of higher concentration to a region of lower concentration
Diffusion
the net movement of particles from a region of higher concentration to a region of lower concentration, moving down the concentration gradient. It will continue until there is an equilibrium. Non polar particles can easily pass through the membrane, however polar ones have difficulty, partial positive and negative ones can diffuse slowly, large surface area compared to volume is important so that materials can diffuse
Steroid hormones
They are lipophilic (fat-loving) meaning they can freely diffuse across the plasma membrane of the cell, they bind to receptors in either the cytoplasm or the nucleus of the target cell to create and active receptor-hormone complex. which goes into the nucleus and binds to the dna, acting as a transcription factor for gene expansion
Factors that effect rate of diffusion
Concentration gradient: the larger the gradient, the higher the rate of diffusion, surface area (e.g alveoli in lungs for gas exchange, membrane folds in mitochondria), length of diffusion path, thicker the membrane the lower the rate of diffusion
Osmosis
Occurs in a partially permeable membrane (i.e cell membrane) When a cell is submerged in water, water molecules pass through the cell membrane from an area of low solute concentration to an area of high solute concentration.
Aquaporin
an integral protein that acts as a pore in the membrane that speeds the movement of water molecules
Solutions
The cell membrane is impermeable to solutes (only water can pass through), if solute concentrations are different on each side of the membrane, water will move either in or out of the cell
Isotonic solutions
Solute concentration inside the cell equals the solute concentration outside of the cell. Equal amounts water move in and out of the cell. Size of the cell remains the same. the will remain in equilibrium
Hypotonic solutions
The solute concentration is inside the cell is greater than outside. When placed in water, lots of water will move into the cell, causing the size of the cell to increase. Lysis may occur (the cell will get to big, causing it to burst and die)
Hypertonic solutions
The solute concentration inside the cell is less than outside the cell. When placed in water, water inside the cell moves out of it through osmosis. The size of the cell decreases and plasmolysis may occur (too much water leaves the cell, causing it to shrivel up and die)
Adaptations of Hyper and Hypo tonic solutions
Many aquatic single-celled organisms have a contractile vacuole that removes any excess water to prevent swelling, we use isotonic solutions for medical procedures and bathing tissues (e.g packing donated organs, eye drops, etc), often saline solution
Osmosis in plant cells
Plant cells tend to be hypertonic relative to their environment, so water tends to move into the cells. This creates hydrostatic pressure (the pressure a fluid exerts on a boundary of a confined space)
Turgor pressure
The pressure exerted against the cell walls of a plant cell.
Turgid cell - The swelling of the cell (vacuole) causes the cell membrane to push against the cell wall. This is necessary for plants to remain upright.
Flaccid cell - When water is lost from the cell, the turgor pressure decreases, and the membrane shrinks away from the cell wall (called plasmolysis).
Facilitated diffusion
Transmembrane (polytopic) proteins recognize particular molecules (large, polar) and help it move across the membrane, the direction it moves depends on the concentration gradient
Channel Proteins
they have a polar interior, allowing polar molecules/ions to pass through, they typically have gates that open and close in response to a chemical signal
Carrier Proteins
they bind to a specific molecule to facilitate its passage, they will change shape to allow transport
Potassium channels in axons
They are voltage-gated, and enable facilitated diffusion of potassium out of the axon. At one stage during a nerve impulse there are relatively more positive charges inside. This voltage causes potassium channels to open, allowing potassium ions to diffuse out of the axon. Once the voltage conditions change the channel rapidly closes again
Chemically gated channels
some channels will open when chemicals, such as neurotransmitters (chemicals that allow communication between neurons and muscles/glands), bind to them.
Nicotinic Acetylcholine
a neurotransmitter that signals muscles to contract. When bound to a receptor, it will allow ions such as Na+, K+, and Ca2+ to pass through the membrane. An autoimmune disorder called myasthenia gravis produces antibodies that bind to acetylcholine receptors, blocking the neurotransmitter, resulting in incomplete muscle movements and responses
Active transport requires ATP
integral protein pumps use the energy from the hydrolysis of ATP to move ions or large molecules across the cell membrane. Molecules are moved against their concentration gradient.
Hydrolysis of the bond releases one phosphate and a lot of energy. Respiration in the cells combine ATP with a phosphate ion to be used for further cellular processes
Types of protein pumps
Uniporter (only one molecule passes through), Symporter (two molecules pass through in the same direction), and Antiporter (two molecules pass through in opposite directions).
The sodium-potassium pump
It follows a repeating cycle of steps that result in three sodium ions being pumped out of the axon and two potassium ions being pumped in. Each time the pump goes through this cycle it uses one ATP
Sodium-Potassium Pump steps
1. The interior of the pump is open inside of the axon; three sodium ions enter the pump and attach to their binding sites.
2. ATP transfers a phosphate group from itself to the pump; this causes the pump to change shape and the interior is then closed
3. The interior of the pump opens to the outside of the axon and the three sodium ions are released
4. Two potassium ions from outside can then enter and attach to their binding sites
5. Binding of potassium causes the release of the phosphate group; this causes the pump to change shape again so that it is only open to the inside of the axon
6. The interior of the pump opens to the inside of the axon and the two potassium ions are released. Sodium ions can now enter and bind to the pump again
secondary active transport
the required energy is derived from energy stored in the form of concentration differences in a second solute. Typically, the concentration gradient of the second solute was created by primary active transport, and the diffusion of the second solute across the membrane drives secondary active transport
sodium-dependent glucose transporter (sodium-glucose linked transport (SGLT))
SGLts are used to transport glucose into the cells, SGLT1 transports glucose into the lining of intestinal cells, and SGLT2 transports glucose into the lining of the nephrons (kidneys) and are responsible for removing glucose from the urine. Glucose would have to be transported against its concentration gradient since there is a higher concentration of glucose already in the cell, requiring ATP. The sodium-dependent glucose transporter works with the sodium-potassium pump, this is called coupled transport.
Steps of sodium-dependent glucose transporter
1. there are more sodium ions outside than inside the intestinal cell due to the sodium-potassium pump
2. Sodium ion and glucose molecules bind to a specific transport protein in the extracellular surface
3. Sodium ions pass through the carrier to the inside of the cell down its concentration gradient, with the carrier energy released by this movement
4. The captured energy is used to transport glucose through the same protein into the cell
Endocytosis
When the cell membrane folds inward, engulfing a small amount of matter from the extracellular fluid bringing it into the cell and forming a vesicle. The vesicle is formed when a small piece of plasma membrane pinches off. Vesicles taken into the cell contain extracellular water and solutes and may also contain larger molecules needed by the cell that cannot pass through the plasma membrane alone.
Phagocytosis
A form of endocytosis; a cell engulfs a large particle along with some of the liquid surrounding it. Occurs only in specialized cells (single-celled amoeba, macrophages) and only when they encounter something suitable for engulfing
Pinocytosis
A form of endocytosis; a cell engulfs a liquid and the small particles dissolved or suspended in it. Occurs in most eukaryotic cells most of the time.
receptor-mediated endocytosis
the intake of molecules that attach to special proteins in the cell membrane which serve as receptors (cholesterol)
Exocytosis
a transport method in which a vesicle fuses with the cell membrane and releases its contents outside the cell into the extracellular environment. Exocytosis is important in cells that specialise in the secretion of various cell products such as hormones, neurotransmitters, and digestive enzymes. E.g specialized cells in the human pancreas secrete the hormone insulin by means of exocytosis. Exocytosis can also be used to get rid of waste products or unwanted materials
steps of vesicles transporting materials using the rough ER, Golgi apparatus and plasma membrane
1. Protein is already synthesized and present in the rough endoplasmic reticulum
2. the protein is moved through the RER and modified
3. A spherical vesicle is formed from the end of the rER with the protein inside
4. the vesicle migrates to the golgi apparatus
5. Vesicle fuses to the cis side of the golgi apparatus, the protein is released into the lumen of the golgi apparatus
6. The Golgi modifies the protein further by adding lipid or polysaccharides to the protein
7. A new vesicle is formed from the trans side of the Golgi membrane which then breaks away. The vesicles migrate to the plasma membrane.
8. The vesicle migrates to the plasma membrane, fuses and secretes its contents out of the cell (exocytosis)
Estimation of osmolarity
The osmolarity of a solution is the total concentration of osmotically active solute. To determine the osmolarity of a tissue, you would need to determine what concentration of solution is isotonic. In an isotonic solution, there is NO change in mass. if the solutions are Hypotonic (increasing the mass) or Hypertonic (decreasing the mass).
compound microscopes
Use multiple lenses to bend light and magnify images.
Benefits: Ease of use, Less expensive to buy, Can observe dead or living cells in color, Cell movement can be studied, Quick specimen preparation (minutes to hours), No need for high voltage electricity
Limitations: Maximum magnification of about 1500X●Low resolving power (0.25μm to 0.3μm
Electron microscopes
Use electron beams focused by electromagnets to magnify and resolve
Benefits: Magnification of 100,000X to 300,000X, High resolving power (0.001μm)
Limitations: Expensive to use, Requires cells to be killed and chemically, No movement can be seen, Without stain or dye, no color can be seen, High voltage electric current is required, Specimen preparation usually takes a few days
Cryogenic electron microscopy
A transmission electron microscopy technique that is used to determine the structure of molecules at near atomic level resolution. A solution with a molecule of interest is frozen and bombarded with a beam of electrons. A computer analyzes patters of diffraction off the sample to produce an image of the structure.
Cytoplasm
Cytosol is the liquid part of the cytoplasm. It is a gel-like fluid substance made of water and many dissolved solutes such as salts, fatty acids, sugars, amino acids, and proteins such as enzymes. These dissolved substances are needed to carry out the metabolic processes required to keep the cell alive. If these molecules were not dissolved in water, they would not be able to perform their function.
Ribosomes
Ribosomes catalyze the synthesis of polypeptides during translation and are composed of two subunits that come together to form a functioning structure. The ribosomes are made from dozens of proteins arranged on a scaffold composed of ribosomal RNA that functions as a ribozyme. Prokaryotes have smaller (70s) ribosomes, whereas eukaryotes have larger (80s) ones. S (svedberg unit) measures particle density. Ribosome structure differences allows for antibiotics to kill prokaryotic cells without affecting eukaryotic ones.
Prokaryotic cell structure
Cell membrane, cytoplasm, ribosomes, cell wall. Pili enables the cell to attach to surfaces, swap DNA with other cells and may be used to harpoon DNA in the environment. Capsules help the cell keep from dehydrating and adhere to surfaces. Flagellum are long extensions used in cell locomotion. DNA can be found in the nucleoid (main dna of the cell, not enclosed in a membrane, floating freely, single loop, not wrapped around proteins "naked") or the plasmid (extra pieces of DNA, circular, naked, smaller than nucleoid, replicates independently, genes for antibiotic resistance)
Eukaryotic cell structure
They are compartmentalized, contain membrane-bound organelles such as the nucleus and mitochondria, the membrane around an organelle creates a compartment with controlled conditions inside (are tailored to the specific functions of the organelle)
Nucleus - Eukaryotic
contains the DNA, which stores information for making proteins via transcription and translation, contains the nucleolus which is where ribosome subunits are made. Has a double membrane with pores through it which allows Eukaryotic cells to separate the activities of gene transcription and translation
Ribosomes - Eukaryotic
they have 80s ribosomes that are either free (floating in the cytoplasm synthesizing polypeptides used within the cell), or bound (attached to the rER, synthesizing polypeptides that are secreted from the cell or become integral proteins in the cell membrane
rough endoplasmic reticulum - Eukaryotic
a series of connected flattened membranous sacs that play a central role in the synthesis and transport of polypeptides. Has bound ribosomes which synthesize the polypeptide and release it to the inside rER. the rER membrane is continuous with the nuclear envelope, which surrounds the cell nucleus
Smooth endoplasmic reticulum - Eukaryotic
is a series of connected flattened membranous sacs that are continuous with the rER. In contrast to the rER, smooth endoplasmic reticulum lacks ribosomes and is not involved with protein synthesis. Its main functions are synthesis of phospholipids and cholesterol for the formation and repair of membranes
golgi apparatus - Eukaryotic
modifies polypeptides into their functional state. It sorts, concentrates, and packs proteins into vesicles. Depending on the contents, the vesicles are dispatched to one of three destinations, within the cell (to organelles called lysosomes), the plasma membrane, and secretion to the outside of the cell via exocytosis
Vesicles - Eukaryotic
they are membrane bound sacs that contain and transport materials within cells. Transport vesicles move molecules between locations inside the cell by budding off one organelle compartment and fusing with another. Secretory vesicles secrete molecules from the cell via exocytosis. They are also how new phospholipids are added to the cell membrane.
Lysosomes - Eukaryotic
small spherical organelles, enclosed by a single membrane. They contain enzymes that work in oxygen-poor areas and lower pH. The enzymes digest large molecules to degrade and recycle the components of the cell's own organelles when they are old or damaged, or if the cell is starving in the absence of nutrients. Also has an immune defense function, by digesting pathogens that have been engulfed by phagocytes
mitochondria - Eukaryotic
Mitochondria are adapted for production of ATP by aerobic cellular respiration. The mitochondrion is surrounded by a double membrane. Mitochondria evolved by endosymbiosis
Chloroplasts - Eukaryotic
Chloroplasts are adapted for photosynthesis, which captures light energy and uses it with water and carbon dioxide to produce glucose. Within the chloroplasts are light-absorbing pigments such as chlorophyll, which give the chloroplast its characteristic green colour. Chloroplasts evolved by endosymbiosis.
vacuoles - Eukaryotic
Mature plant cells have a central vacuole that occupies 30% - 90% of the volume of the cell. In addition to water storage, the main role of the vacuole is to maintain turgor pressure against the cell wall. The turgor pressure is mechanism the plants use to remain upright
Cytoskeleton
Present in both prokaryotic and eukaryotic cells, the cytoskeleton is not considered to be an organelle. The cytoskeleton helps cells maintain their shape, organizes cell parts and enables cells to move and divide. Several different components work together to form the cytoskeleton, including Microtubules, Actin filaments, and Intermediate filament
Microtubules
Microtubules are polymers of a protein called tubulin and form part of the cytoskeleton. Microtubules are used for the intracellular transport of organelles and the separation of chromosomes during mitosis
centrioles
Centrioles are paired cylindrical-shaped organelles composed of nine groups of three microtubules organized with radial symmetry. Functions of centrioles include: Arrangement of the mitotic spindle during cell division, anchor points for microtubules in the cytoplasm and for cilia and flagella (when modified to become a basal body). A few eukaryotic cell types have lost their centrioles including most fungi and vascular plants
Cillia and Flagella
Cilia and flagella are extensions from the cell surface which aid in cell movement. They are formed from modified centrioles called a basal body. If the protrusions are short and numerous they are termed cilia. Cilia beat in coordination with each other. If the protrusions are longer and less numerous (usually only one or two) they are termed flagella. Flagella move independently of eachother
Homeostasis
A function of life; living organisms keep their internal environments within a certain range (maintain a stable internal condition), despite changes in their external environment. Even single-celled organisms maintain homeostasis, for example by keeping concentrations of water and minerals within certain levels.
Metabolism
A function of life; it is the sum of all the chemical reactions in a cell. Viruses lack metabolism, a reason they are not considered to be self-sustaining life
nutrition
a function of life; all life obtains energy and matter. Autotrophs use external energy sources (usually the sun) to synthesize carbon compounds from simple organic compounds. Heterotrophs use carbon compounds obtained from other organisms to synthesize the carbon compounds that they require.
Movement
A function of life; adaptations for movement are a universal feature of living organisms. Sessile organisms stay in one place, whereas motile organisms are mobile.
excretion
a function of life; it is a process in which metabolic waste is eliminated from an organism. In humans, excretion primarily occurs via lungs and kidneys. In many plants, excretion occurs via leaves, roots and stem. In unicellular organisms, excretion occurs through the cell membrane, which is the one reason cells must have a large surface area to volume ratio
Growth
a function of life; all living things can grow/develop the lifespan. Growth is the increase in size and mass of an organism. Development is the transformation of the organism through its lifespan.
Response to stimuli
A function of life; all life can recognize and respond to changes in environmental conditions. They can do this through chemoreceptors (stimulated by changes in chemical concentration of substances), baroreceptors (stimulated by changes in pressure), thermoreceptors (stimulated by changes in temperature), and photoreceptors (stimulated by light energy)
Reproduction
A function of life; sexual reproduction involves two parents and the fusion of haploid sex cells from each parent. Asexual reproduction involves only one parent, produces offspring that are genitically identical to the parent, binary fission and mitosis are mechanisms of it.
Paramecium - functions of life
Metabolism – most metabolic pathways happen in the cytoplasm
Nutrition – food vacuoles contain organisms the paramecium has consumed, then broken down and then absorbed into the cytoplasm
Growth – after consuming and assimilating biomass from food the paramecium will get larger until it divides.
Reproduction – The nucleus can divide to support cell division by mitosis, reproduction is often asexual
Response – the wave action of the cilia moves the paramecium in response to changes in the environment, e.g. towards food.
Homeostasis – contractile vacuole fill up with water and expel it through the plasma membrane to manage the water content
Excretion – the plasma membrane control the entry and exit of substances including expulsion of metabolic waste
Chlamydomonas - functions of life
Metabolism – most metabolic pathways happen in the cytoplasm and chloroplasts
Nutrition – photosynthesis happens inside the chloroplasts to provide the algae with food
Growth – after consuming and assimilating biomass from food the algae will get larger until it divides.
Homeostasis – contractile vacuole fill up with water and expel I through the plasma membrane to manage the water content
Response – the wave action of the cilia moves the algae in response to changes in the environment, e.g. towards light due to light sensitive eye spot
Reproduction – The nucleus can divide to support cell division, by mitosis (these cells are undergoing cytokinesis). The nuclei can also fuse and divide to carry out a form of sexual reproduction
Excretion– the plasma membrane control the entry and exit of substances including the diffusion out of waste oxygen from photosynthesis
Differences in eukaryotic cell structure
Animal and plant are multicellular, fungi can be unicellular. Animal cells lack a cell wall, plants have one made of cellulose, fungi have one made of chitin. Plants are autotrophs (make their own food), animals are holozoic (eat other things), and fungi are saprotrophs (they absorb enzymes that they secrete into their environment). Animals have the largest kingdom
Trends vs discrepancies
Trends lead to the development of productions of what we expect to observe, they are a prevailing tendency, a generalization, and typical (e.g cells are small). Discrepancies do not fit the general trend, and can lead to scientific questions
Examples of discrepancies in cells
Red blood cells - during their maturation, they discard their nucleus and mitochondria, making them very small and increasing their surface area to volume ratio for efficient gas exchange, and ability to move through narrow capillary vessels.
Aseptate fungal hyphae - are sometimes not divided up into individual cells, resulting in a continuous cytoplasm along the length of the hyphae
Skeletal muscle - skeletal muscle fibre cells result from the fusion of multiple unicellular cells, resulting in a large cell that has multiple nuclei.
Phloem sieve tube element - specialized cells that are part of the phloem. They lose their nucleus and other organelles during their development, allowing them to have more space for transport of phloem sap.
Advantages of Eukaryotic cells being compartmentalized
Efficiency of metabolism - enzymes and subtances for a particular process can be localized and much more concentrated
Toxic/damaging substances can be isolated - substances harmful to the cell can be contained within the membrane of an organelle
Localized conditions - pH and other factors can be kept at optimal levels. Ideal conditions for a particular process can be maintained in certain areas of the cell
Numbers and locations of organelles can be changed - organelles with their contents can be moved around within the cell and changed dependent on the requirements of the cell
Nucleus - cell compartmentalization
generally spherical with a double membrane (nuclear envelope), pores are present in the membrane, contains genetic information (chromosomes), uncoiled chromosomes are referred to as chromatin, the nucleolus is a small, dense region inside the nucleus where proteins and rRNA join to form ribosomes. Compartmentalization keeps chromosomes safe, in prokaryotes there is no nucleus so protein synthesis happens immediately. Having a double membrane prevents phospholipids from being exposed to water, and allows for the creation of a large pore for materials to pass in and out of the nucleus, and allows membrane to break down and reform during mitosis and meiosis
Mitochondria - cell compartmentalization
smooth outer membrane and a folded inner membrane called the cristae, the fluid-filled space in the inner membrane is called the matrix. The outer membrane makes sure the mitochondrion is a specialized compartment for ATP production, cristae increases surface area for production, and the intermembrane space between the inner and outer ones is where a high concentration of protons is generated. Matrix contains enzymes and substrates needed for rapid biochemical reactions.
Chloroplasts - Cell compartmentalization
double membrane, filled with a fluid called stroma, inside are stacks of thylakoids (one stack called a granum), each thylakoid is a disc composed of flattened membrane and contains chlorophyll. The grana are connected by tubes called lamella. Large surface area of the thylakoid membranes ensures that a lot of light will be absorbed. A small volume of space for the proton gradient (inside and outside of thylakoids) allows it to develop after absorbing just a few photons of light
Golgi apparatus - cell compartmentalization
consists of flattened membrane sacs called cisternae, in plant cells it synthesizes pectin for cell walls, in animal cells it produces lysosomes. The vesicle transport model suggests the cisternae do not move and vesicles transfer proteins between them. The cisternal maturation model suggests vesicles from the rER coalesce to form new cisternae on the cis side, which then gradually move through the golgi until they reach the trans side, where they break up into vesicles.
Clathrin
a three-legged protein that becomes positioned on the inner face of the plasma membrane when a vesicle is being made. Adjacent clathrin molecules bind to each other to form a lattice of pentagons/hexagons, allowing the plasma membrane to become indented and eventually detach to form a sphere of membrane with a clathrin cage around it (vesicles)
Gametes
Many organisms come from the fertilization of two gametes. Gametes are the sex cells that fuse together during sexual reproduction, they have haploid nuclei, so in humans both egg and sperm cells contain 23 chromosomes. The fertilized egg cell (zygote) is a diploid cell containing two of each chromosome. After the zygote is formed, the cells will start to divide by mitosis and eventually form an embryo, at this point cells are unspecialized but they will eventually differentiate and become specialized for different functions
Differentiation of cells
All diploid cells of an individual organism share an identical genome (each cell contains the entire set of genetic instructions for that organism), but not all genes are expressed (activated) in all cells. newly formed cells receive signals from morphogens which deactivate genes. Active genes are usually packaged in an expanded and accessible form, while inactive genes are mainly packaged in a condensed form. The fewer active genes a cell has, the more specialized it will become.
Stem cells
unspecialized cells that can continuously divide and replicate, and have the capacity to differentiate into specialized cell types.
totipotent cells
are Stem cells capable of continued division and possess the ability to produce any tissue in the organisms. They only exist in the very early stages of embryo development. Could produce a whole organ. In totipotent embryonic stem cells the entire genome is active
pluripotent
they only exist in early embryonic stage. They can mature into almost all the different cell types. Would not be able to produce a whole organism
Multipotent
can differentiate into a few closely-related types of cell. They can occur later in the embryo development and are present during the remainder of an organism's life.
unipotent
Can regenerate but can only differentiate into their associated cell type (ex. liver stem cells can only make liver cells)
Types of stem cells
There are two types of stem cells: embryonic (can differentiate into any kind of cell, considered pluripotent), and tissue (sometimes called adult stem cells, exist within specialized tissue, only able to differentiate into certain types of cells)
Stem cell niches
Stem cells have two unique properties, they can self renew (can divide and become more stem cells, or a mixture of stem and differentiated, allows them to be maintained), and they can recreate functional tissues (signaling will turn on and off certain genes to cause cells to become differentiated), stem cell niches are the locations in which many stem cells can be found (bone marrow creates blood cells alongside self-renewing cells) and hair follicles (creates epithelial stem cells at the bottom, multipotent)
Therapeutic cloning
stem cells can be used to replace damaged or diseased cells with healthy ones. This process requires the use of biochemical solutions to trigger differentiation to the desired type, surgical implantation of the cells into the patient's tissue, suppression of host immune system to prevent rejection of cells, careful monitoring of new cells to make sure they don't become cancerous. Lukemia (bone marrow transplants for patients who are immunocompromised due to chemotherapy) Paraplegia (repair damage caused by spinal injuries to give movement to paralyzed victims) diabetes (replace non-functioning islet cells with those capable of producing insulin), burn victims (new skins cells)
Ethical issues involving stem cells
Ethical considerations involving stem cells depends on the source. The greatest yield of pluripotent stem cells comes from embryos, but requires the destruction of a potential living organism. The source of these embryonic stem cells comes from laboratories carrying out in vitro fertilization. Not all fertilized eggs are implanted so the rest will be used for research
size of cells
dictated by the basic processes of cell physiology, such as need for materials to move in and out of the cell, involves surface area to volume ration. Cell division apparatus, if cells are too large or too small, the mitotic spindle will not function properly
Red and white blood cells adaptations
they contain hemoglobin that combine and release oxygen, they have a biconcave disc which increases surface area for absorption, lack a mitochondria and nucleus, are flexible and size limited to get through capillaries
White blood cells retain their nucleus, there are several different types of them, possess vesicles with enzymes to kill microorganisms and break down their cellular debris that they obtain through phagocytosis
Neurons adaptations
there are several types of neurons each with distinct adaptations for their functions, motor neurons carry impulses from the brain or spinal cord to muscles and glands, they have long fibres called axons that can carry impulses up and down the body over long distances
striated muscle fibre adaptations
they are up skeletal muscle, each fibre has its own cell and it contains membranes that allow signal propagations, they can be up to 12 cm long and are longer than cardiac and smooth muscle cells, they can have multiple nuclei
Surface area to volume ratio
cells do not grow indefinitely, they reach a maximum size and then they divide. A factor called the surface area to volume to ratio limits the size of cells, the rate of metabolism in a cell is a function of its volume, as the size of a cell increases, the ratio between the surface area and volume decreases.
Organisms maximizing SA: Vol Ratio
as organisms grow, cells divide. Two small cells are more efficient than one large cell, which also allows for cell differentiation, specialized functions, and multicellular life. Cells compartmentalize, using membranes to carry out metabolic processes. In eukaryotes, these are called organelles. E.g intestines fold up to make food absorbtion more efficient, alveoli in lungs are thin membranes to maximize surface area for gas exchange
Magnification
Image of size/image of specimen, image size = magnification x actual size of specimen, actual size of specimen = size of image/magnification.
To calculate the size of a specimen divide field of view by how many times you think the specimen fits into the field of view
Field of view, high power: (diameter at low power x magnification of low power objective)/ magnification of high power objective