bio 207 lecture 4-5
what gave rise to eukaryotes
archaea swallowing bacteria
what are prokaryotes. what are the two. what are their DNA
unicellular, that lack a nucleus and memebrane bound organelles, no histone proteins/or nucleosomes, not highly ordered and packed. bacteria and archae. circular DNA
what are eukaryotes. what are ex. what is there dna
both unicellular and multicellular with memebrane bound organelles such an mitochondria and ER. genetic material is surronded in a nuclear envelope to form a nuclues. animals,. plantws, fungi and protists. DNA is closely associated with histones to form tightly packed chromosomes.
are viruses cells
no, they are neither prokaryotic or eukaryotic
what is a virus
a virus replicated within living cells, it consits of. genetic material (nucleic acid) surrounded by a protein coat.
how do prokarytoic cells reproduce
through binary fision
how does binary fission work
asexual reproduction where two identical daughter cells divide, results in two genetically identical offspring because it is the seperation of the replicated circular chromsome and the origins of replication move to opposite ends till they are anchroed to opposite sides.
do prokarytoes have a high rate of replication
yes
what is a diploid
msot eukaryotic cells, diploid cells carry two sets of genetic info
what is haploid
haploid cells carry one set of genetic info
humans have ___ chromsomes and ___ pairs of homolgous chromsomes
46, 23
what are the.4 strucutral components of a chromosome
telomere, centromere, homologous chromosomes, sister chromatids.
is a chromsome only one chromatid or 2 chromatids
both sometimes 1 chromatid and sometimes 2 chromatids
what is the centromere
a constricted region of the chromosome where the kinetochores form and spingle microtubulues attach
what is a kinetochore
protein strucutre located on centromere. attaches the chromosome to the spindle fibers which help seperate that chromosomes into daughter cells during mitosis and meiosis. ensures accurate chromsome movement and segregation
what are spindle microtubules
protein fibers that form part of the miotic spindle during clel division,responsible for moving/segregating chromsomes into duaghter cells. they extend from centromeres and attach to kinetochores, helping to align and pull them apart.
what is the cell cycle
what leads to the division of a cell intwo two duaghter cells. consits of interphase (G1,S, G2) and mitotic phase (mitosis and cytokinesis). regulates cell growth, dna replication and cell division
what happens during G1 phase of the cell cycle? what about the G1 checkpoint
the cell grows
synthesizes proteins
carries out normal metabolic functions
prepares for DNA replication in the S phase
G1 checkpoint ensures the cell is ready for DNA synthesis
what is G0
cells may enter this phase before the G1 checkpoint, it is a non dividing phase
what happens during the S phase of the cell cycle
in the S phase, the cell replicates its DNA. each chromosome is duplicated, resulting in two sister chromatids for each chromosome. this ensures that each daughter cell will have a complete set of chromsomes
what happens during the G2 phase of the cell cycle
in G2, cell continues to grow and prepares for mitosis. it synthesizes proteins needed for cell division. the G2 checkpoint check for DNA integrity and ensures that the cell is ready for mitosis
what is the pupose of the cell cycle checkpoint
ensure that the cell is progressing correctly through the stages of division. they monitor for DNA damage , proper DNA replication and cell size. if there are errors, the cycle will be paused to fix issues before moving onto the next phase
what is mitosis , product, stages.
M phase, procces of nuclear division that results in two genetically identical daughter cells. prophase, metaphase, anaphase, telophase. chromsomes are aligned, seperated and distributed to each daughter cell.
what is cytokinesis
final step of cell division, where the cytoplasm of the parent cell is divided into two daughter cell. occurs after mitosis and ensures that each daughter cell has its own set of organelles and enough resouces to survive.
interphase
where the cell prepares for division, G1, S, G2. cell grows , replicates its DNA and synthesizes proteins necersary for cell divsion. checks for errors before movin onto mitosis
what happens during prophase
- the chromatid condenses into visible chromosomes by condensins
- nuclear membrane begins to break down
- spindle fibres start to form from the centrosomes
- centrosomes move toward opposite poled of the cell, preparing for chromsome alignment
what happens during prometaphase
- nuclear envelope broken
- spindle fibers attach to kinetochore
- chromsomes beging moving bc they are beign pulled by spindle fibres, are gradually aliging in the centre
what is centriole
cylindrical structure made of microtubules. organizes the microtubules that make up the spindle. each cell typically has a pair of centrioles near the nucleus in the centrosome region
what is a centrosome
region of the cell that organizes mictrotubles and contains a pair of centriole. acts as the main microtubule oragnizing center, organizes the miotic spindle to ensure proper chromosome seperation
what are spindle microtubule made of
tubulin subunits, that get added to the plus end elogating the microtubule and when they shorten these units are removed from the same end this is called depolymerization. what allows movement.
metaphase of mitosis
the spindle assembly checkpoint, chromsomes align along the equator (metaphase plate), the spindle fibers which are attached to the centromeres of each chromsome via the kinetochore, ensure that the chromsomes are properly positioned for seperation. ensure the that each daughter cell will receive an identical set of chromosomes
anaphase of mitosis
dissaembly of tubulin and motor proteins, sister chromatids of each chromosme are pulled apart toward opposite poled of the cell. centromere splits, spindle fibers shortern, seprating the chromatids. each daughter cell will receive a complete set of chromosomes
telophase of mitosis
seperated chromatid reach opposite poled of the cell, beging to de condence back into chromatin. nuclear membrane re forms around each set of chromsomes, creating two new nuclei. prepares cell cor cytokinesis
what is the end result of the cell cycle
two gentically identical cells who are also identical to the cell that gave rise to them, contain full complement of chromosomes, and approx half the cytoplasm and organelle content of the original parent cell
what happens to chromsome fragments that lack centromeres
a chromsome breka can produce a chromsome fragment that lacks a centromere during mitosis this fragment cannot attach to the spindle microtubule and is usually lost from the nucleus
from G1, S<G2, prophase/prometaphase, metaphase, anaphase and telophase/cytokinesis , list the number of chrosomes per cell and the number of DNA molcules per cell
chromsomes: 4,4,4,4,4,8,4
dna molecules: 4,4-->8,8,8,8,8,4
what holds the two dna molcules together
through the function of a set of proteins called cohesions
proper sister chromatid segregation depends on cohesions... why?
cohesion complex (forms rings at DNA replication stage), when the two chromatid seperate in ana phase the seperase cleaves cohesion subunit
what are homologus pairs of chromosomes
two chromosomes one from each parent that have the same structure, size and genetic content. they carry the same genes but may have different alleles of thos genes
what are sister chromatids
two identical copies of a single chromosome that are connected by a centrometer. formed during dna replication, remain attached until theya re seperated during cell division
how do homolgous pairs of chromosomes differ from sister chromatids
homologous chromosomes are a pair of chromosomes one from each parent that are similar but not identical. sister chromatids are identical copies of the same chromosome
mitosis vs meiosis
mitosis: cellular reproduction
meiosis: produce gametes for sexual reproduction
is interphase the same in mitosis and meoisis
yes
middle prophase I- meiosis I
homolgous chromsomes begin to pair up, forming tetrads ( group of 4 chromatids), the chromatids of homoglous chrosome undergo genetic recombination (crossing over) where sections of chromatids are exchanged inc genetic diveristy
late prophase I of meoisis I
nuclear membrane breaks down, spindle fibres begin to form. the tetrads fully connected to the spindle fibres. chromatids from different chromsome exchnaged genetic material and begin to move toward the metaphase plate
synapsis? tetrad?
close pairing of homoglous chrosomes, after pairing called a tetrad which is closely associated four sister chromatid of two homologus chromosomes
crossing over
during middle prophase I, when homoglous chromosone exchnage sections of chromatids. first mechanism of generating genetic variation in newly formed gametes
metaphase I
tetrads (pairs of homologous chromosomes) line up along the metaphase plate. homologous chromosomes are randomly arranged which leads to independent assortment this increases gentic variety.
anaphase I
spindle fibres shorten, pulling homolgous chromosomes to opposite poles of the cell. each chromsomes still consister of two sister chromatids but the homoglous chromosomes are now seperated.
telophase I
the seperated chromosomes reach opposite poles of the cell. nuclear memebrane starts to reform around each set of chromosomes. cytokinesis typically follow dividing the cell intwo two haploid daughter cells each with half the number of chromosomes.
what happens betwen meiosis I and meiosis II
interkinesis
prophase II
nuclear envelope dissolves in both haploid cells, spindle fibres beging to form. the chromsomes which still consist of chromatids start moving towards M plate.
metaphase II
chromosomes lines up along M plate in both haploid cells. unlike metaphase I the chromosomes are not in homologous pairs but individual chromosomes are aligned for separation
anaphase II
centromeres divide, sister chromatids pulled to opposite poles of the cell similar to anaphase in mitosis but in haploid cells
telophase II
chromatids arrive at opposite poles, nuclear membrane reforms around chromosomes, cells divide through cytokinesis resulting in 4 haploid daughter cells each witha single set of chromosomes
end product of meiosis II
4 haploid cells each with half the chromosome # of the original diploid cell. these cells are geneticcaly unique because of crossing over during Meiosis I and the independent assormtent during both divisions
before meosis the cell is _, after meoisis I the cell is_, after meosis II the cell is _
2n diploid with 2n chromosomes and 2n DNA molecules
n (haploid) but each chromsomes still consists of two sister chromatids so 2n dna molecules
n , 4 haploid cells each with n chromsomes and n dna molecules
proper chromosome and sister chromatid segregation depends on cohesins, why?
cohesion complex different subunit for meosis, theres some around the chiastma that holds homoglous pairs of chromsomes together and ones around centromere that holds sister chromatids together. in anaphase I the ones between homoglous chromsomes breaks and anaphase II the shugoshin in between sister chromatids break
describe meosis in male gametogensis. from spermatogonium, to spermatocyte, to secondary spermatocyte, to spermatif
spermatogonoium (2n)- mitosis
primary spermatocyte (2n)- meiosis I, prophase I rest of meoisis steps
secondary spermatocytes (1n)- 2
meosis 2
spermatids (1n)- 4
in woman for female gametogensis, oogonium, primary oocyte, secondary oocyte (first polar body), ovum and second polar body
oogonium (2n)- mitosis
meoisis I and prophase I
primary oocyte (2n)- arrested in prophase I till puberty
meoisis I rest of phase
secondary oocye (1n) and first polar body- cytokineses occures, still contain 1n
meoisis II
ovum (1n) and secondary polar body (1n)
fertilziation-> zygote (2n)
what is the end result of meiosis
4 daughter cell that are genetically variable from each other and their parent, that have hald the number of chromsomes, half cytoplasm, half organelles.
what are the two forms of genetic varation in meiosis
random segregation of chromosomes durign meiosis I and homolgous recombination (crossing over) that both happen in meiosis I
what is random segregation
maternal and paternal chrosomes are randomyl distributed bc homolgous chrosomes randomly align along the metaphase plate during metaphase I and then seperate into different daughter cells
cohesion compelx proteins is part of what cmplex
synaptonemal complex
what is necessary for hologmous chrosomes to seperate properly during meiosis I
atleast 1 crossovr is necessary in every homoglous pair for proper seperation
what are the two models of homoglous recobmination
1. holliday junction and single strand break
2. double strand break model of recombination
consequences of homoglous recombination 2 pros 2 cons
dna repair- hr repairs DSB maintaing genomic stability
genetic diveristy
cons:
chromsomal rearrangement can lead to translocations, inversions, deletions
can cause genomic instability through chromosome loss or apoptosis
holiday junction resolution- in the oduble strand breka model
a double strand break occurs, blue tries invading red but jsut elongates it and gets in its space, the displaced loop is used as template reconnect the blue. involves the cleavge of HJ by resolvaes, followed by ligation resulting in cross over or non crossover products.
difference between holiday model and double stranded break model
holiday model beings with single strand nicks in homoglous chrosomes leadign to strand invasion and HJ formation
DSB model, starts with double strand break in one DNA molecules which is processed to create single stranded 3' overhang to invade a homoglous DNA moleucles leading to HJ formation. doubel HJ formation
somatic mutations
mutations in somatic tissues, dies with indivual carrying the mutation
germ line mutations
mutations in the germ cells, heritable, passed onto the next gen
mutations that effect a single gene
base sub, insertion/deletions, expanding nucleotide repeats
base substibution- transition is
purine to purine, more common than transversion
A->G
G->A
C->T
T->C
base sub transversion
pur-> prymidine or prymiidine--> pur whatever combo A->C A--> T... so on
what causes this base subs
spontaneous replication eroors, chemical chnages, mutagens
rare base tautomers, anaomalous base pairing arrangments or nonstandard base pairing that result in wobble
bases that are isomer C-A T-G
base deletion
everything shifts forward
base insertion
everything shifts downward
insertions and deletions are more frequent than base subs
yes
depurination
loss of purine, from the original strand, a wrong nucleotide is use when replicating the empty spot (most often A), then when it mutates to T in RNA which is now permanent mutation and the other strand with the empty mutates to an A with the empty spot
deamination
loss of an amino group, C--> U, end result both are T and top is A
strand spligage
looping out leads to inseritons and deletions
if homoglous chromosomes cross over unequally
one cross over contains insertion and the other deletion
expanading nucleotide repeats (3 main diseases)
set of nucleotides that increase in copy number, fragile X syndrome (CGG) 50-1500, huntington disease (CAG) 37-12 ampyotrophic later sceloris (GGGGCC) 7-16
protein code is
degenerate, redudnant, 3rd base more relaxed
base subs can cause
missense (change in amino acid), nonsense (stop), silent
in frame mutation
set of 3 insertered or deleted
condtional muation
pheno seen under certain conditons
gain of function mutation
usualyl dominant- one copy in diploid produced a phenotype, gains new functioon
supressor mutation
mutation that hides or suppresses the effect of another mutation
intrageneic
same gene as original mutation
intergenic
in a different gene as the original mutation
mutation A-B- hides what
mutation A- B+ which causes white yes but -- is red eyes
if it brings it back to the same protein the intragneic suppresor is it work
yes
intergenic
different site , different gene , codes for functional even after. astop codon from the earlier muation
mismatch repair, for small loops and other lesions
enzymes cut out newly made dna, and replace it with new nucleotides . knows the template strand is the methylated one
direct repair
restors the correct chemical strucutre of altered nucleotides
base excision repair
glycolaze remove specific types of damaged bases, and the section (AP site) of the polynucleotide is replaced
nucleotide excision repair
removes and replaces any types of damaged DNA, two strands of DNA seperated, section of the DNA containting distortion is removed, DNA polymerase fills in the gap and DNA ligase seals the filled in gap
homology directed repair
uses sister chromatid to repair break, same as ds break modle of homoglous recomb
non homolhoous end joining
last resort reapir mechanism for cell, no template used, error. prone.
abnroma cell proliferation, which is regularlay well regulated
cancer
werener syndrome
defect in homogloous recombination
xeroderma pigmentosum
freckle spots on skin, predispostion to skin cancer
aneuploidy- trisomy
(2n+1) 1 extrra
translocation
a segement of a chromsome moves to a non homolgous chromsomes, or to another place on the same chromo
red green colour blindess
unequal crossing over during homoglous recobmination, deletion of green opsin
during propphase one problems lining up causes
loops
gene dosage
alters the relative amounts of interacting products, cause devlopmental problems
heterzygous deletions
if centromere is deleted, whole chromsome is lost. unmasks recessive mutations
haploinsufficeny
one copy of gene is not enough
homozygous deletion
often lethal
signiciance of polyploidy
inc cell size, larger plant attributes, might give rise to new species
allopolyploids may arrise from
hybridication between two species followed by chromosome doubling
autotriploid
homogloous chromsomes pairing in more than 1 way creating unequal chromo numbers
autoploidy
nondisjunction in meiosis I produces 2n gamete
autotetraploid
no cell division in mitosis
autoploidy
from single species
polyploidy
one or more complete sets of chromsomes are added (3n,4n..)
genetic mosacicism for sex chromo does what
produces a gynandromorph XX and XO
effects of aneuploidy
usuually lethal, gene dosage effect but no change in actual DNA sequence, down syndroms is a result. sometimes canceours cells
monosomic- aneuploidy
2n-1
aneuploidy during meiosis 1
trisomic and monosomic result
nondijunction in meiosis 1
diploid, trisomic and monosomic results
causes of aneuploidy
deletion of centromere during mitosis and meiosis so loss of chromosomes, usualyl very lethal but sometimes x chromsomes are the exception
duplications are important for
evolution one cupy can do its original fucntion the other is free to mutate ex. globin genes
inversions
niether lsot nor gained genetic material b ut dna seuence changes. reduces rates of recombination
inverstions paracentric
inverstion that does not icnlude centrometre in the inverted region