Chapter Eleven Flashcards
What is the first event in cell division?
Reproductive signal - initiates cell division (intracellular or extracellular)
-this signal is most always extracellular in prokaryotes
What is the second event in cell division?
Complete replication of DNA
What is the third event in cell division and what happens?
Segregation - the distribution of DNA into each of the cells
What is the fourth even in cell division?
Cytokinesis - separation of cellular material into two new identical cells -the true division part
What is prokaryotic cell division called?
Binary fission - it results in the reproduction of an entirely new single-celled organism.
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.
Explain prokaryotic chromosomes.
Most have one single chromosome, consisting of single molecule of DNA, often circular but folded
They have two important regions,
the ori (origin) where replication starts
the ter (terminus) where replication ends
How does the reproductive signal differ in prokaryotes and eukaryotes?
In prokaryotes, the signal is external factors like nutrient concentration and conditions outside, these directly speed up division
In eukaryotes, cells do not constantly divide when the conditions inside or outside are great
the signals are related to the needs/function of the entire organism
What are sister chromatids?
they are newly replicated chromosomes closely associated with one another
the indicative X shape means replication has happened
What is mitosis?
it is the process that actually segregates newly-replicated chromosomes into two new nuclei
the roles include, helping grow and develop, repairing tissues, regenerate lost body parts, and reproduce asexually
what are the broad stages of the cell cycle
- Interphase (involves cell growth, followed by DNA synthesis, and then more cell growth (most of the life of the cell is in this 23 hours interphase)
- Mitosis
- Cytokinesis
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 second sub-phase and what happens?
S (between G1 and G2 phase)
the DNA replicates, sister chromatids remain together
What is the third sub-phase and what happens
G2 (between S phase and mitosis)
the cell prepares for mitosis, by double checking to make sure replication was flawless
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.
What type of proteins are involved in regulating the restriction point?
CDKs are enzymes
cyclins are allosteric activators
RB is inhibitory protein
What is a kinase?
A kinase is an enzyme that catalyzes the transfer of a phosphate group from ATP to a target protein.
What is phosphorylation?
it is the addition of a phosphate group.
What are cyclin dependent kinases?
they are kinases that are always present, but their default is inactive
their chief purpose is to control the progress of the cell cycle
What are cyclins?
they are allosteric activators/regulators of CDK
by binding to CDK they alter the shape of the active site and activate it
they become present when the CDKs need to be activated
What is the RB protein?
the protein that normally inhibits the cell cycle at the restriction point
but when it becomes phosphorylated it becomes inactivated and it no longer blocks the cell cycle
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 G0?
G0 is when cells are in an “inactive” resting phase, if they aren’t preparing for cell division
example would be heart and brain cells
How does a cell in G0 re-enter G1?
They must be stimulated by a growth factor.
Growth factors are proteins that activate signal transduction pathways that end with cyclin synthesis and thereby start the cell cycle back up
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 does each nucleosome have?
proteins in a core of about 8 histone molecules
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
What does the X shape of a chromosome indicate?
it indicates that replication has happened
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 are condensins?
they are large proteins that coat DNA molecules and make them more compact
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 are kinetochores and when do they develop on each sister chromatid?
They are specialized structures found on each chromatid that are important for chromosome movement
are developed in late prophase and attached to the kinetochore microtubules
What are polar microtubules?
they DO NOT attach to the chromatid and instead overlap in the middle of the spindle to form the framework
What are kinetochore microtubules?
they attach to kinetochore structures and to microtubules in opposite poles and partially pull them to the respected poles
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 are centrosomes?
they are organelles located near the nucleus that organize the microtubules
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 importance of APC?
APC activates separase, the enzyme that hydrolyzes cohesion during anaphase (the glue that holds the sister chromatids together at the centromere)
Well functioning APC make sure DNA is separated from the original sister chromatid
What are daughter chromosomes?
they are separated chromatids that are now chromosomes that have their own centromere
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
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
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 happens after cytokinesis?
the new daughter cells enter interphase so the cycle can repeat
What are somatic cells?
they are body cells that are not specialized for reproduction
each somatic cell has homologous pairs with each parent contributing one homolog to the offspring
What are homologous pairs?
they are matching pairs of chromosomes that carry same sequence of genes for the same traits.
What are gametes and what do they contain?
they are sex cells created by meiosis, and they broadly contain the DNA that will passed to the next generation but more specifically, only one set of chromosomes (one homolog of each pair)
What is a zygote?
it is a cell that is created by the fusion of two gametes, aka a fertilized egg
What is fertilization?
the combination of sex cells (gametes)
when two haploid gametes (n) fuse to form a diploid (2n) zygote
What is the process by which a zygote (fertilized egg) grows?
mitosis
What is the difference between haploid and diploid?
haploid (n) is the chromosome number
diploid is when 2 haploid gametes fuse (2n)
What type of cells undergo meiosis?
sexually reproducing eukaryotic cells (germ cells)
What cells are produced from meiosis?
haploid germ cells (sperm and egg cells) (gametes)
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 Chiasmata?
they are regions of attachment that form between non-sister chromatids (SEE PICTURE)
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 diversity
What is the second phase of meiosis I and what happenes?
- 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 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
What is a human example of nondisjunction?
an example is aneuploidy trisomy 21 which is commonly know as down-syndrome
What are the differences between mitosis and meiosis?
- Mitosis consists of one stage, meiosis two
- Mitosis results in the production of a diploid, while
Meiosis results in the production of a haploid - Mitosis generates two identical diploids
Meiosis generates two genetically diverse haploids - Mitosis is results in somatic cells
Meiosis is results in sex cells
What is apoptosis?
it is programmed cell death
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 is metastasis?
when cancer cells invade surrounding tissue and travel through the blood stream or lymph system
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
