Lecture 2/10 Flashcards
why does elongation eventually stop in PCR?
because the polymerase is only good for a certain number of nucleotides
what is special about round 3 of PCR amplification?
you start ending up with more fragments the exact size of your target gene, and these smaller pieces amplify faster
At what temperature does denaturation happen?
94 degrees
What is taq polymerase good at?
extension
what is taq polymerase bad at?
proofreading, it is missing critical residues for 3’ to 5; exonuclease alpha activity
how do we get around taw polymerases bad proofreading?
taq is usually used along with another thermal stable polymerase that is good at proofreading
when can you see chromosomes?
during mitosis
what does condensin ii do and at what stage?
acts during prophase to make large loops to condense, makes the chromosomes visible
what does condensin i do and when?
acts during metaphase to make smaller loops within the larger loops
when does the nuclear envelope break down?
starts during prophase and finishes in metaphase
what happens in prophase?
centrosomes move to opposite poles and nucleoli begin to disappear
what are centrosomes?
specialized microtubule organizing center (a pair of centrioles, perpendicular to each other)
what is MTOC responsible for?
nucleating more microtubules – there are tubulin subunits that are polymerized into microtubules
what happens in prometaphase?
nuclear envelope breaks down and microtubules from MTOC invade the nuclear region
once the nuclear envelope breaks down, what does condensin i do?
it further condenses the chromosomes
what 2 things happen when the microtubules from MTOC invade the nuclear region?
- mitotic spindles form from 3 types of microtubules
- sister chromatids must attach to microtubules from different poles
what are the 3 kinds of microtubules?
astral (stay at the poles), kinetochore, polar
do microtubules go all the way across the cell?
no, they interdigitate
which side (+ or -) of mitotic spindles can have subunits removed?
both
which side of the mitotic spindle sees faster growth?
the + side
what happens in metaphase?
sister chromatids attach to spindle fibers from opposite poles and align on metaphase plate
why do chromosomes move to the metaphase plate?
because they’re being pulled in both directions
do chromosomes bind directly to microtubules?
no
why does metaphase take a long time?
chromatids must attach correctly, and nothing will divide until everything is correct
what is a centromere?
constricted region of chromosome with specialized, repeated, satellite DNA sequences (CENP-B box
when are the complexes like CENP box created?
G2
What are CENP-B boxes
a specific DNA sequence that centromere protein B binds to, playing a role in centromere form and function
what happens during anaphase?
centromeric proteins divide and chromosomes move to the separate poles
in what order do centromeric proteins divide?
they divide nearly simultaneously
do all chromosomes move to the poles at the same time?
no, they move at slightly different rates, which helps them set up chromosome territories within the cell
how do chromosomes travel to the poles?
along microtubules – as the chromosome moves to the poles, the middle microtubule starts to depolymerize because they have to be gone for cell division
when does cytokinesis occur?
it begins during anaphase but isn’t completed until the end of telophase
what 3 things happen in cytokinesis?
- the parent cell splits into 2 daughter cells with identical DNA content
- the nuclear envelope starts to form again
- DNA starts to de-condense
once cytokinesis occurs, are the 2 daughter cells exactly the same?
the DNA content is the same, but the cytoplasmic content might not be equally distributed, which can give the cells different cellular fates
what protein complex helps keep the chromatids together after replication?
cohesin
when is cohesin lost?
when polo comes in to phosphorylate sonorin
which parts of the cell cycle is cohesin around for?
all of them
how do chromatids attach to spindle fibers?
via kinetochores
what are kinetochores?
complexes of proteins associated with the centromere, it’s where the microtubules of the spindle fibers attach
at what point must cohesin molecules be cleaved?
during anaphase, as the motors in kinetochores move chromosomes along microtubules to different poles in the cell
what is ploidy?
the number of sets of chromosomes in the nucleus
what is a genome?
sum of genetic information in a cell
what does n represent?
one full set of chromosomes of an organism
how many chromosomes are around in metaphase? and what is n?
the amount of the somatic cell, 4n
how many sister chromatids are around during metaphase?
double the number of chromosomes that are around (for 4n)
how many chromosomes are around during anaphase? what is n?
double the amount from metaphase, 4n
how many sister chromatids are around during anaphase?
none
how many sister chromatids are around after telophase?
none
how many chromosomes are around after telophase? and what is n?
whatever the diploid number of chromosomes is, 2n
what is the goal of meiosis?
take a diploid germ cell and make it haploid (half the DNA content)
Does sperm have an X or Y chromosome?
it can carry either
how is genetic diversity generated in meiosis?
recombination – independent assortment
what is gametogenesis?
formation of gametes
what is the germ line?
specialized diploid cells set aside during embryogenesis that undergo mitosis to generate more germline cells and then mitosis to generate gametes
do all cells in the germ line go through meiosis?
they go through mitosis to make more germ line cells and once they make the switch to meiosis, they can generate gametes
what is the result of meiosis ii in women? men?
1 egg or 4 sperm
when does recombination occur and what is it between?
in meiosis i, between sister chromatids of homologous chromosomes
after chromosomes have duplicated and are going to go through meiosis, how do the chromosomes organize?
the homologous chromosomes align
what holds the homologous chromosomes together?
synaptonemal complex that forms between the sister chromatids of homologous chromosomes
