CELL BIOLOGY HL BIO
function of cell membrane
transport raw materials into the cell and manufactured products/waste out of the cell, prevent entry of unwanted matter into cell, prevent escape of matter needed, plasma membrane acts as a barrier, and regulates the movement of molecules and ions in/out of the cell
phospholipid bilayers
phospholipids form bilayers in water due to the amphipathic properties of phospholipid molecules. The head is hydrophilic whereas the tail is hydrophobic. A bilayer is when they arrange themselves so that the tails are tucked away from the water and the heads are directed towards the water. It is very stable because of the bonds formed between the phosphate heads and the surrounding water and also because there is a weak intermolecular interaction in the tails.
emergent properties of phospholipid bilayers
phospholipids will self-organize to keep heads wet and tails dry. They can flow past each other laterally, NOT vertically.
Davson and Danielli (1930s)
A protein-lipid sandwich. proteins do not permeate the lipid layer and are on the outside of the sandwich. To get a clear image of the structure, it involves the rapid freezing of cells and then fracturing them along lines of weakness.
Sunger-Nicholson fluid mosaic model
Peripheral proteins are bound to either the inner or outer surface of the membrane. Phospholipid molecules form a membrane (fluid and move laterally). Integral proteins permeate the surface of the protein. The modern version features a phospholipid bilayer with proteins either bound on the surface or to other proteins/lipids (like glyco-lipids/proteins).
Proteins
Integral proteins are permanently embedded and are either polytopic or monotonic. They are amphipathic.
Functions of membrane proteins
TRACIE:
Transport - protein channels/pumps
Receptors - peptide-based hormones
Anchorage - cytoskeleton attachments
Cell recognition - MHC proteins and antigens. provide cell labels
Intercellular joining - tight junctions
Enzymatic activity - metabolic pathways
Cholesterol
Allows membrane to function in a wider range of temperatures (cause of interactions between tails of bilayer). Hydroxyl group makes it polar/non-polar. Steroid. Non-polar tail attracted to centre of membrane where there are phosphate non-polar tails.
Membrane Fluidity
Tails usually act as a liquid, while the heads act as a solid. If too fluid, the membrane cannot effectively restrict the movement across itself. But, must be fluid enough so that they can move.
Fatty acid membrane fluidity
There is a weak bond since only the heads can bond to water, which allows phospholipids and proteins to move freely. Unsaturated fatty acids are more ideal in lower temperatures (cause kinks and weakly packed). Saturated fatty acids are more ideal in higher temperatures (cause straight and tightly packed).
Bacteria membrane fluidity
Cannot maintain a constant internal temperature, and therefore are more susceptible to changes in temperature. Fatty acid desaturases are enzymes that convert saturated into unsaturated fatty acids when the temperature begins to cool.
Cholesterol membrane fluidity
Restricts movement of molecules (reducing membrane fluidity). Disrupts regular packing of tails and molecules (increasing flexibility as it prevents the tails from crystalizing and behaving as a solid). Reduces the permeability to water-soluble molecules/ions. Stabilizes membranes at higher temperatures and maintains flexibility at lower temperatures. The endoplasmic reticulum will have more cholesterol cause its more subjected to extreme temperatures.
Cell-Adhesion Molecules
Help things like skin and muscles bind tightly. type of CAM depends on cell-to-cell junction.
Desmosomes form sturdy but flexible sheets of cells in organs.
Channels can be used to anchor cells together and allow ions to pass between for communication.
Plasmodesmata are tubes connecting the cytoplasm of adjacent cells that allow exchange of materials like water
Membrane transport
They are selectively permeable (diffusion, active transport, endo-exo-cytosis). Non-polar go through easy, polar diffuse slowly, and positive/negative ions cannot easily pass through. Large surface area compared to volume is important.
passive transport a) simple diffusion
Diffusion is the net movement of particles from high to low concentration - moving down the concentration gradient. This will continue to happen until there is an equilibrium.
a) simple diffusion - steroid hormones
lipophilic, meaning they can freely diffuse across plasma membrane. They bind to receptors in either cytoplasm.nucleus to form an active receptor-hormone complex, then will move into nucleus and bind to DNA to aid as a transcription factor for gene expression. Ex. estrogen, testosterone, etc.
a) simple diffusion - factors that affect rate of diffusion
Larger concentration gradient = higher rate of diffusion.
Larger surface area = higher rate of diffusion. (alveoli for gas exchange, vili for absorption, root hairs for water intake)
Thicker membrane = lower rate of diffusion
passive transport b) osmosis
When a cell is submerged in water, the water molecules pass through the membrane from low (outside) to high (inside) solute concentration. Aquaporin! Membrane is impermeable to solutes, so only water can pass through.
ISOTONIC: Equal osmolarity
HYPOTONIC: Lower osmolarity (water moves into the cell and lysis may occur)
HYPERTONIC: Higher osmolarity (water moves out of the cell and creation may occur)
A contractile vacuole helps remove and excess water in a cell! (this is an adaptation common in aquatic single-celled organisms). Plants are usually hypertonic which creates hydrostatic pressure and tugor pressure. Tugor pressure decreases when water is lost and then the membrane shrinks away from the cell wall (plasmolysis). Plant dies.
passive transport c) Facilitated Diffusion
Large molecules can't get across the membrane via simple diffusion. Transmembrane proteins recognize a particular molecule and help it move across the membrane. Facilitated diffusion is the movement of molecules from high to low concentration across a cell with the help of a carrier protein.
- channel proteins have polar interiors and have gates that open and close in response to chemical signals.
- carrier proteins bind to a specific molecule to facilitate its passage. they'll change shape to allow transport.
c) Facilitated Diffusion - Chemically gated channels
neurotransmitters bind to channel to open it. nicotinic acetylcholine is a transmitter and will allow Na, K, and Ca to pass through the membrane (when bound to receptors). Autoimmune system disorder Myasthenia gravis - produces antibodies that bind to the acetylcholine receptors, blocking them and causing incomplete muscle movement.
active transport a) requires atp
intergral protein pumps use the energy from hydrolysis of ATP to move ions across the cell membrane. Molecules move AGAINST the concentration gradient.
Uniporter: one molecule passes through
Symporter: two molecules pass through in the same direction
Antiporter: two molecules pass through in different directions
ATP
Hydrolysis of the bond releases one phosphate and a lot of energy.
Respiration in the cells combines ADP with a phosphate ion, to be used for further cellular processes.
a) primary transport - the sodium-potassium pump
Repeating cycle of 3 Na being pumped out of the axon (of neurons) and 2 K being pumped in.
1. interior pump is open to inside the axon, 3 Na enter the pump and attach to binding sites
2. ATP transfers a phosphate group to the pump, pump changes shape then interior closes
3. interior pump opens to outside the axon, 3 Na released
4. 2 K enter from outside and attach to binding sites
5. Binding of K causes release of phosphate group, pump changes shape to be open to inside the axon
6. interior pummp opens to inside the axon and K are released.
a) primary transport - sodium-glucose linked transport (SGLT)
Used to transport glucose into cells. SGLT1 is for lining of intestinal cells whereas SGLT2 is for lining of kidneys (removing glucose from urine). Against concentration gradient since here is a higher concentration INSIDE the cell already. requires ATP. Couples transport with sodium-potassium pump.
1. more Na outside than inside intestinal cell due to pump
2. Na and glucose bind to specific transport protein in the extracellular surface
3. Na pass through the carrier to inside the cell down its concentration gradient. the carrier captures energy released in this movement
4. captured energy is used to transport the glucose through the same protein into the cell
Vesicles
small spheroidal packages that bud off of the RER and the golgi apparatus. They carry proteins produced by ribosomes on the RER to the gogli where they are prepared for export from the cell via another vessicle.
1. transport vesicles: move molecules between locations
2. secretory vesicles: secrete molecules from the cell via exocytosis
Endocytosis
cell folds inwards and engulfs a small amount of matter from the extracellular fluid and brings it into the cell, forming a vesicle. the vesicle is carrying extracellular matter that is to big to bring through the plasma membrane.
Phagocytosis = cell eating. engulfs a large particle. only in specialized cells.
Pinocytosis = cell drinking. engulds liquid and small particles. occurs in most eukaryotic cells.
Exocytosis
vesicle fuses with the cell membrane and releases its content outside the cell in the extracellular environment. important in cells that specialize in the secretion of various cell products (like hormones, transmitters, etc). Can be used to get rid of waste products in cell.
How vesicles are used to transport materials within a cell between RER, golgi, and plasma membrane
Protein is already synthesized and in rER. protein moved and modified. vesical formed from the end of rER with protein inside. vesicle migrates to golgi. vesicle fuss to cis side of golgo. protein is released into the lumen of golgi. golgi modifies the protein by adding lipid or polysaccharide. new vesicle formed from the trans side of golgi which then breaks away and migrates to plasma membrane. vesicle fuses and secretes content out of the cell. EXOCYTOSIS
Cell theory
1. all living organisms are composed of one or more cells
2. cells are the smallest units of life
3. all cells come from pre-existing cells
Inductive reasoning
theories developed from observations using specific observations to form a general conclusion
Deductive reasoning
using general premise to form a specific conclusion
what is common to all cells?
plasma membrane, cytoplasm, DNA, ribosomes
Cytoplasm
dissolved solutes and proteins and enzymes. they are needed to carry out metabolic processes required to keep the cell alive.
DNA
RNA is hypnotized to be the first genetic material to evolve, all living organisms use DNA today.
Ribosomes
catalyzes the synthesis of polypeptides during translation. destination of polypeptides is golgi. they are composed of two subunits that come together to form a functioning structure. in prokaryotes 70s. in eukaryotes 80s. no membrane. small subunit binding site for mRNA. large subunit three binding sites for tRNA.
Free = floating in cytoplasm synthesizing polypeptides inside the cell
Bound = attached to the rRER, synthesizing polypeptides secreted from the cell
Prokaryotic cell structure
cell membrane, cytoplasm, cell wall, pili, capsule, flagellum
Pili
enable the cell to attach to surfaces, swap DNA with other cells, and harpoon DNA in the environment.
Capsule
helps cell keep from dehydrating and adhere to surfaces
Flagellum
Long extensions used in cell locomotion
DNA in prokaryotic cells
1. Nucleoid: main DNA of the cell. freely in the cytoplasm, no nucleus, naked (no proteins), single loop.
2. Plasmid: extra pieces of DNA. not in all prokaryotic cells. gene for antibiotic resistance.
Eukaryotic cell structure
they are compartmentalized with membrane-bound organelles such as the nucleus and mitochondria. an organelle creates a compartment with controlled conditions inside.
Contains: nucleus, ribosomes, rRER, sRER, golgi, vesicles, lysosomes, mitochondria, chloroplasts, vacuoles, cytoskeleton, microtubules, centrioles, cilia, and flagella.
Nucleus
double membrane with pores to separate the activities of gene transcription and translation. Contains DNA (protein synthesis) and nucleolus (ribosome subunits). Genetic info in the form of chromosomes. ribosomal RNA join to form subunits of ribosomes.
rough endoplasmic reticulum
connected flattened membrane sacs. synthesis and transport of polypeptides.
smooth endoplasmic reticulum
connected flattened membrane sacs that are continuous with RER and. Lacks ribosomes. Synthesis of phospholipids and cholesterol.
Golgi apparatus
modifies polypeptids into their functional state. maufactures carbohydrates. concentrates and packs proteins into vesicles. get sent either to lysosomes, plasma membrane, or exocytosis secretion. protein moves from the left side (cis) to right side (trans).
Vesical transport model: cisternae don't move and vesicles transfer proteins between them.
Cisternal maturation model: vesicles coalesce to form new cisternae on cis side which then move through golgi until reach trans side where they break up into vesicles.
Lysosomes
enzymes that work in oxygen-poor areas and lower PH. digest large molecules to degrade and recycle components of old/damaged cells. Digests pathogens that have been engulfed by phagocytes.
Mitochondria
adapted for photosynthesis of ATP by aerobic cellular respiration. double membrane. double membrane. smooth outer but folded inner membrane referred to as cristae. fluid inside the inner membrane is called the matrix.
Chloroplasts
adapted for photosynthesis, capturing light energy and using it with water and carbon dioxide to produce glucose. double membrane. fluid called stroma. stacks of thylakoids (stacks are called granum). grana is connected by tubes called lamella. each thylakoid is a disc of a flattened membrane with chlorophyll.
Vacuoles
central vacuole in plants. water storage and maintains tugor pressure.
Cytoskeleton
maintain cell shape, organizes cell parts, and enables cells to move and divide
Microtubules
polymer of protein called tubulin and forms a part of the cytoskeleton. used for the intracellular transport of organelles and separation of chromosomes during mitosis.
Centrioles
arrangement of the mitotic spindle during cell division, anchor points for microtubules and cilia/flagella
Cilia and Flagella
extensions from the cell surface which aid in cell movement. Cilia are short and work in coordination with each other. Flagella are long and work independently.
Homeostasis
keep cells internal environments within a certain range (ex. temperature, concentration of water/minerals, etc)
Metabolism
sum of all chemical reactions in a cell
Nutrition
all cells obtain energy and matter. Autotrophs vs heterotrophs.
Movement
sessile organisms stay in one place whereas motile organisms are mobile.
Excretion
Metabolic waste is eliminated from organism. lungs/kidneys, leaves/roots/stem, and cell membrane.
Growth vs Development
Growth is the increase in size and mass of an organism
Development is the transformation of the organism through its lifespan
Response to stimuli
Chemoreceptors: stimulated by changes in the chemical concentration of substances
Baroreceptors: stimulated by changes in pressure
Thermoreceptors: stimulated by changes in temperature
Photoreceptors: stimulated by light energy
Sexual vs Asexual reproduction
sexual: two parents and the fusion of haploid sex cells from each. meiosis. offspring are genetically unique.
asexual: one parent. mitosis and binary fission. offspring are all genetically identical to parent.
Eukaryotic differences; Animalia vs Fungus vs Plantae
animals are all multicellular eukaryotes without a cell wall. they are holozoic.
fungus are eukaryotes with a cellwallmade of chitin. can be unicellular or multicellular. are saprotrophs. principal decomposers.
plants are multicellular eukaryotes with a cellulose cell wall. autotrophs.
similarities between animal, fungi, and plant eukaryotic cells
nucleus, free and bound 80s ribosomes, rER, sER, golgi apparatus, vesicles, lysosomes, mitochondria, cytoskeleton.
Differences between animals and fungi and plants eukaryotic cell
Plastids: only in plants
Cell wall: plants and fungi
Vacuoles: in all of them
Centrioles: in all, but barely fungi
Cilia and Flagella: in all but barely fungi and plants
Trends vs Discrepancies
Trend: prevailing tendancy, a generalization. lead to development of predictions of what we expect to observe.
Discrepancy: from trends and lead to scientific questions
Discrepancy examples
Red blood cells: by discarding nucleus and mitochondria for maturation, they shrink which increases their surface area to volume ratio for gas exchange. DISCREPANCY: a eukaryotic cell without a nucleus or mitochondria.
Skeletal muscles: result from fusion of multiple unicellular cells. results in one large cell that has multiple nuclei. DISCREPANCY: a very large eukaryotic cell with more than one nucleus.
Phloem since tube element: sive tubes lose their nucleus and other organelles during development to have more space for transport of phloem sap. DISCREPANCY: a eukaryotic cell without organelles.
single/double/no membrane organelles
single: vesicles, vacuoles, rER, sER, golgi, lysosomes
double: nuclei, mitochondria, chloroplasts
no: ribosomes, centrioles, microtubules, nulcleoli
Advantages of eukaryotic cells being compartmentalized
efficiency of metabolism: enzymes localized and concentrated
toxic/damaging substances can be isolated: contained withing membrane
localized conditions: pH and things can be kept at optimal levels
numbers and location of organelles can change: organelles can move around within cell
Advantages of separating nucleus and cytoplasm
Eukaryotes: allows for mRNA to be modified in nucleus before exiting into the cytoplasm for next process in protein synthesis
Prokaryotes: don't have a nucleus. DNA and ribosomes come together in the cytoplasm and protein synthesis occurs instantly
It also keeps the chromosomes inside nucleus safe.
Double membrane
there is hydrophobic core of single-layer phospholipids. if exposed to water, crazy damage occurs.
Clathrin
Three legged protein on the inner face of the plasma membrane (where a vesicle is being made). bind to each other (lattice).