Unknown Material Exam Four Flashcards
What are the four events of cell division?
- Reproductive signal - initiates cell division (intracellular or extracellular)
-this signal is most always extracellular in prokaryotes - Complete replication of DNA
- Segregation - the distribution of DNA into each of the cells
What are the steps of binary fission?
- Reproductive signal - things outside the cell signal to start the cycle, examples include nutrient concentration and environmental conditions
- Replication - it occurs as DNA moves through a replication complex of proteins; replication starts at the ori (origin) and ends at the ter (terminus)
in rapidly dividing prokaryotes, this process occupies the entire time between divisions
- Segregation - when the ori regions move towards the opposite ends of the cell, the ter ends are in the center most part, and the daughter DNA molecules are segregated
- Cytokinesis - the cell membrane is pinched in and protein fibers form a z ring, then the cell walls / membranes are synthesized to form two new cells.
What is the first sub-phase of interphase and what happens?
G1 (between cytokinesis and S phase)
chromosomes are single (not yet replicated) and associated with proteins (restriction point)
What is the restriction point?
it is the checkpoint when it commits to DNA replication and subsequent cell division
checks for mutations and damage etc. after it becomes committed to replication.
Are the CDK’s Cyclins, and Inhibitory proteins all the same throughout the cell cycle?
No there are many different cyclin CDK complexes during the different stages, but they have similar mechanisms for activation/continuation of the cycle.
What is a nucleosome?
DNA molecules that are packed into bead-like units called and are formed by the interaction of proteins called histones
What is a chromatin?
the complex of DNA molecules bound with many proteins
What is a chromosome?
It is a bundle of tightly coiled DNA located in the nucleus of every eukaryotic cell
Explain the importance of cohesin.
they are proteins that hold together the newly replicated chromosomes (sister chromatid) during G2
should be separated by separase by activation of APC in anaphase
When mitosis happens the cohesion is removed except where?
the centromere (the location in the middle of the chromosomes that hold together the sister chromatid.
What is the first phase of mitosis and what happens?
- Prophase - when the chromosomes condense, the spindles assemble, and the centrosomes move to opposite ends of the nuclear envelope
What is the second phase of mitosis and what happens?
- Pro Metaphase - when the nuclear envelope breaks down and all the cohesion is removed except at the centromere
also the chromosomes attach to the spindle at the kinetochore
What is the third phase of mitosis?
- Metaphase - when chromosomes align on the equatorial/metaphase plate
What is the fourth phase of mitosis?
- Anaphase - when the sister chromatids separate and become daughter chromosomes which then start to migrate towards the poles
This is controlled by M - phase cyclin cdk
when cyclins are created, they allosterically activate the cdks which in turn activate APC by phosphorylation
What is the fifth phase of mitosis?
- Telophase - when the daughter chromosomes reach the poles - the actual segregation of mitosis
When telophase ends, the nuclear envelopes and nucleoli reform, and the chromatin (previously daughter chromosomes) decondense and the microtubules detach here
What is the difference between daughter chromosomes and sister chromatids?
sister chromatids share a centromere, while daughter chromosomes have their own centromere
i.e daughter chromosomes are separate, sister are together
Explain animal cell cytokinesis.
when a contractile ring of microfilaments of actin and myosin forms to pinch the cell membrane between the daughter cells
Explain plant cell cytokinesis.
when vesicles from the Golgi apparatus appear along the plane of the cell division, and the vesicles fuse to form a new plasma membrane
the contents of the vesicles also form a cell plate, the beginning of a new cell wall
What are homologous pairs?
they are matching pairs of chromosomes that carry same sequence of genes for the same traits.
“a pair of chromosomes” one from mom and one from dad
What is the first phase of meiosis I and what happens?
- Prophase I - the chromatin begins to condense and the centromeres align
Synapsis also happens which is specific parallel alignment (pairing) of homologous chromosomes
Tetrads also form which are four chromatid that make up the pair of homologous chromosomes
What is the second phase of meiosis I and what happens?
- Prometaphase I - or (late prophase) when crossing over happens at the chiasmata and recombinant chromatids form and the microtubules attach to the kinetochore
What is the third phase of meiosis I and what happens?
- Metaphase I - when the homologous pairs line up at the equatorial (metaphase) plate
What is the fourth phase of meiosis I and what happens?
- Anaphase I - when the homologous chromosomes (each with two chromatids) after separation move to opposite poles of the cell
What is the fifth phase of meiosis I and what happens?
- Telophase I - when the chromosomes gather into nuclei and the original cell divides through cytokinesis
What is crossing over?
it is the exchange of genetic material between non-sister chromatids at the chiasmata
this results in recombinant chromatids (re combined two things into something new) chromatids and increases the genetic variability
What is independent assortment?
when chromosome pairs align randomly during metaphase one
i.e one side could be all blue and the other all red or it could be a random mixture of the pairs
What is the first phase of meiosis II and what happens?
- Prophase II - chromosomes condense again after a brief interphase but there is NO replication of DNA
What is the second phase of meiosis II and what happens?
- Prometaphase II - the chromosomes are attached to kinetochores microtubules at the kinetochore
What is the third phase of meiosis II and what happens?
- Metaphase II - the centromeres of the paired chromatids line up along the equatorial plate of each cell
What is the fourth phase of meiosis II and what happens?
- Anaphase II - the sister chromatids separate and become chromosomes, moving to opposite poles
What is the fifth phase of meiosis II?
- Telophase II - when the chromosomes gather into nuclei and the cells divide in cytokinesis
product of cytokinesis in meiosis II is four separate cells with a nucleus with a haploid number of chromosomes
What is nondisjunction?
non- disjunction literally means no separation
it is when homologous pairs fail to separate at anaphase I (APC) and as a result, sister chromatids fail to separate in meiosis II
which results in aneuploidy - chromosomes that lacking or present in excess
Why is apoptosis important?
It can get rid of cells that are no longer needed
(like the connective tissue of the hand of a fetus)
Or other old cells that are prone to genetic damage and are beyond repair, so they don’t cause cancer
What initiates apoptosis?
hormones, growth factors, viral infections toxins, and extensive DNA damage all do
the signals act through signal transduction pathways
What is a benign tumor?
they are masses of cells that
- grow slowly
- resemble the tissue they grow from
- are encapsulated and remain localized
What is a malignant tumor?
are masses of cells that:
1. do not resemble the parent tissue
2. often have irregular structures
3. are not encapsulated which leads to metastasis
What are oncogenes?
positive regulators in cancer cells
normal regulators become mutated to be overactive or present in excess
What are tumor suppressors?
they are negative regulators such as RB that fail to inhibit the cell cycle and become inactive in cancer cells
What is an allele?
they are alternate forms of a gene
example is R and r, which are the same gene but just different forms
Explain the (P), (F1), and (F2) generations in Mendel’s original round and wrinkled seeds.
generation started with a dominant homozygous and a recessive homozygous
F1 the resulting offspring of P is all heterozygous, which are self-bred
F2 the result of two heterozygotes gives the 3 to 1 phenotypic ratio of and the 1 to 2 to 1 genotypic ratio
Explain the P, F1 and F2 in the dihybrid cross of seed shape and color.
P in this scenario was the homozygous dominant RRYY and the homozygous recessive rryy
F1 resulting from P was all heterozygotes RrYy
F2 shows a 9:3:3:1 phenotypic ratio, but 9 different genotypes show in a 16 punnet square in which the RY, Ry, rY, and ry gametes are bred
What was the significance of Mendel’s first law?
that our genes occur in pairs and segregate from each other during formation of gametes
the law of segregation entails that two copies of a gene separate during gamete formation (one copy per sex cell)
What was Mendel’s second law?
the law of independent assortment which states that copies of different genes on the gametes assort independently (shown by the dihybrid cross)
What is the multiplication rule?
the probability of two independent events happening together can be found by multiplying the probabilities of the events together
eg. getting a heads two times flipping coins is a 1/4 odds (1/2 x 1/2)
What is the addition rule?
the probability that an event can occur in two different ways is just the sum of the separate probabilities
eg. chances of getting a heads OR a tails in one turn (1/2 + 1/2) = 1
What is true breeding?
when the parental generation has the same exact genotype in order to show the same phenotype in the next generation
e.g would be HH with another HH or yy with yy
What is incomplete dominance?
when alleles are neither dominant or recessive, so heterozygotes have a new intermediate phenotype,
alleles have not blended and the original phenotypes will show up later down the road
MORE PHENOTYPIC DIVERSITY
what is co-dominance?
when more than one allele codes for a functional protein,
dominant R red allele and dominant W white allele come together to have red and white spots or vice versa
MORE PHENOTYPIC DIVERSITY
What is a mutation?
it is a stable inherited change in genetic material
-alleles that are not wild types are mutant alleles.
What is a locus?
it is the specific location of a gene on a chromosome
What are linked genes?
since many genes are found on a single chromosome, when genes are physically linked they reveal inheritance patterns that aren’t mendelian
example is the fruit flies where color of bodies and size wings were linked genes and so the recessive pairs and dominant pairs showed a different ratio than the 1 to 1 to 1 to 1 predicted
What is Pleiotropy?
is when one allele has multiple phenotypic effects
example would be Marfan syndrome, which is caused by variation in the FBN1 gene, people with Marfan syndrome tend to be tall with long thin fingers, toes and limbs.
What is epistasis?
is when the phenotypic expression of one gene is influenced by another gene
example is that alleles for black and brown dogs aren’t expressed unless the E allele is expressed bbEe and BbEE are brown and black dogs respectively
What is the effect of the environment on phenotype?
Light, temperature, nutrition, etc. effect the expression of genotype
What is significant about Siamese cats and rabbits in reference to environmental effect?
There is point restriction coat patterns in them where enzymes that produce dark fur are inactive at higher temps
therefore the nose ears are cooler so they appear darker
How can prokaryotes exchange genes?
they exchange genes when the DNA of a donor cell passes to recipient cell through “conjugation”
DNA often lines up and crossing over occurs, changing the makeup.
What are plasmids?
they are small circular chromosomes that can
1. move between cells during DNA transfer
2. can replicate independently of main chromosome
What kind of genes do plasmids contain?
- genes that code for unusual metabolic functions, like breaking down hydrocarbons
- genes that code for antibiotic resistance
- genes that code for making a sex pilus
What are the purines?
they are nitrogenous bases that are two rings fused and are adenine and gUanine
What are the pyrimidines?
they are single ringed nitrogenous bases and they include cytosine and thYmine (and in RNA also Uracil)
When does replication start?
when the pre-replication complex of proteins bind to the origin of replication
What are the single stranded binding proteins?
they work with the DNA helicase to keep the separate strands from folding back
What are primers?
the primer is a short starter strand, usually RNA, that is complementary to the DNA template so the polymerase can grab onto it
What are the three DNA repair mechanisms?
- Proofreading: DNA polymerase recognizes mismatched pairs and removes incorrectly paired bases
- Mismatch repair: newly replicated DNA is scanned for
mistakes by other proteins, and mismatches can be corrected - Excision repair: enzymes scan DNA for damaged bases –they’re excised and DNA polymerase I adds the correct ones
What is PCR?
Polymerase chain reaction (PCR): an automated process that makes multiple copies of short DNA sequences for genetic manipulation and research i.e amplifying small amounts of DNA
