C2 - Reproduction Flashcards
In animals, autosomal cells are said to be what?
Diploid (2n) - they contain 2 copies of each chromosome
Germ cells are….
Haploid (n) - contain only 1 copy of each chromosome
How many chromosomes do we inherit from each parent
23
the Cell cycle consists of what 4 stages (in order)
G1,S,G2,M
The first 3 stages of the Cell Cycle are known as…
Interphase - the largest part of cell cycle
Cells that do not divide spend all of their time in an offshoot of G1 called…
G0 - the cell is simply living and carrying out its functions, without any preperation for division
During Interphase, individual chromosomes are in a less condensed form known as what? why are they in this less condensed form?
Chromatin - this is because the DNA must be available to RNA polymerase so that genes can be transcribed
During Mitosis, why is it preferable to condense the DNA into tightly coiled chromosomes?
to avoid losing any genetic material during cell division
What happens during G1 Stage of the Cell cycle?
-cells create organelles for energy and protein production, also increase their size
-Passage into the S(synthesis) stage is governed by a restriction point - certain criteria, such as containing the proper complement of DNA, must be met for the cell to pass the restriction point and enter the S stage
What happens during S stage of the Cell cycle?
-the cell replicates its genetic material so that each daughter cell will have identical copies
after replication of the genetic material in the S stage what is each chromosomes composition?
each chromosome consists of 2 identical chromatids bound together at a specialized region known as the centromere
after the S stage do humans still have 46 chromosomes?
Yes, even though 92 chromatids are present; cells entering G2 have twice as much DNA as cells in G1
What happens in the G2 stage of the cell cycle?
-the cell passes through another quality control checkpoint, the cell chekcs to ensure that there are enough organelles and cytoplasm for two daughter cells
-also checks to make sure that DNA replication proceeded correctly to avoid passing on an error to daughter cells
What happens in the M stage of the cell cycle?
-Mitosis- consists of 4 stages: prophase, metaphase, anaphase, telophase
-cytokinesis - the splitting of the cytoplasm and organelles between the 2 daughter cells
what happens at the G1/S checkpoint (restriction point)?
the cell determines if the condition of the DNA, is good enough for synthesis, if there has been damage to the DNA, the cell cycle goes into arrest until the DNA has been repaired
What is the main protein in control in the G1/S checkpoint?
a protein called P53
What happens at the G2/M checkpoint?
the cell mainly is concerned about ensuring that it has acheived adequate size and the organelles have been properly replicated to support 2 daughter cells
-P53 also plays a role in this checkpoint
What molecules are responsible for the cell cycle?
Cyclins, and Cyclin-dependant kinases(CDK)
For CDK’s to be activated they require the presence of what?
The right Cyclins
During the cell cycle, concentrations of various cyclins increase and decrease during specific stages, what do these cyclins bind to and create?
They bind to CDK’s creating an activated
CDK-Cyclin complex
What is the gene that produces P53? and what happens if it gets mutated?
TP53 is the gene that produces P53, if mutated it causes the cell cycle to not stop repairing damaged DNA - this allows mutations to accumulate resulting in cancerous cells to divide continuously
often cancer cells undergo rapid cell division, creating…
tumors
cancer-causing genes can often be classified into what?
Oncogenes- genes that, when mutated, actively promote cell division
-Tumor suppresor genes- genes that when mutated, lose their ability to regulate or arrest the cell cycle
Mitosis occurs in what cells?
Somatic cells, or cells that are not involved in sexual reproduction
Key concepts of phases in mitosis
Prophase - chromosomes condense, spindle forms
Metaphase - chromosomes align
Anaphase - sister chromatids separate
Telophase - new nuclear membranes form
What is the first step of prophase?
Condensing of chromatin into chromosomes
In prophase what does centriole pairs do?
Separate and move toward opposite poles of the cell
What happens once centrioles migrate to opposite poles of the cell?
They begin to form spindle fibers - made of microtubules
What are the 2 microtubules organizing centers of the cell?
Centrosome, and the basal body of a flagellum or cilium
Some microtubules form asters, what do asters do?
Anchor the centrioles to the cell membrane
What dissolved during prophase?
The nuclear membrane, allowing the spindle fibers to contact the chromosomes
What becomes less distinct in prophase?
The nucleoli and may disappear completely
What are kinetochores?
They are protein structures located on the centromeres that serve as attachment points for specific fibers of the spindle apparatus(kinetochores fibers)
What happens at the metaphase (in depth)
Centriole pairs are now at opposite ends of the cell
Kinetochores fibers interact with the fibers of the spindle apparatus to align the chromosomes at the metaphase plate (equatorial plate) - equal distant from the 2 poles
What happens in the anaphase? (In depth)
-Centromeres split so that each chromatid has its own distinct centromeres, thus allowing the sister chromatids to separate
- sister chromatids are pulled toward the opposite poles of the cell by the shortening of the kinetochore fibers
What happens in telophase? (In depth)
-Spindle apparatus disappears
-a nuclear membrane forms around each set of chromosomes
-nucleoli reappears
-chromosomes uncoil to their interphase form
-each of the 2 new nuclei receive a complete copy of the genome identical to the original genome and each other
When does cytokinesis occur?
At the end of telophasr
What does cytokinesis allow?
Allows each daughter cell enough material to survive on its own
Each cell undergoes a finite number of what?
Divisions before programmed death, after that the cell can no longer divide continuously
What does the CDK-cyclin complex do once activated?
It phosphorylates target proteins, regulating key events in the cell cycle, such as DNA replication and chromosome segregation. This ensures orderly progression through the cell cycle phases, maintaining proper cell division control.
Key factors in prophase (mitosis)
Chromosomes condense, nuclear membrane dissolves, nucleoli disappears, centrioles migrate to opposite poles and begin forming the spindle apparatus
Key factors in metaphase (mitosis)
Chromosomes gather along the metaphase plate in the center of the cell under the guidance of the spindle apparatus
Key factors in anaphase (mitosis)
Sister chromatids separate, and a copy of each chromosome migrates to opposite poles
Key factors in telophase and cytokinesis (mitosis)
Chromosomes decondense, nuclear membrane reforms, nucleoli reappear, Spindle apparatus breaks down, cell divides into 2 identical daughter cells
What do somatic cells and germ cells undergo?
Somatic cells undergo mitosis
Germ cells undergo meiosis
Main difference in Mitosis vs meiosis
Mitosis is 1 round of replication and division, meiosis is 1 round of replication followed by 2 rounds of division
Meiosis 1 results in homologous chromosomes being seperated, generating haploid daughter cells; this is known as…
Reduction division
Meiosis 2 results in the separation of sister chromatids without a change in what? What is this known as (process wise)
Ploidy, process is known as equational division
Definition of ploidy
The number of sets of chromosomes in a cells nucleus, commonly denoted as haploid (n) for 1 set or diploid (2n) 2 sets
What are identical strands of DNA called
Sister chromatids
The human genome is composed of hoe many homologous paired of chromosomes?
23
After the S phase in humans how many chromatids, chromosomes, and homologous pairs are there?
There are 92 chromatids, 46 chromosomes, and 23 homologous pairs
In prophase 1 of meiosis homologous chromosomes do what?
Come together and intertwine in a process called synapsis
During synapsis in prophase 1 of Meiosis what is the form of the chromosome?
It consists of 2 sister chromatids so each synaptic pair contains 4 chromatids and is referred as a tetrad
What holds homologous chromosomes together during synapsis in prophase 1 of meiosis?
A groups of proteins called the synaptonemal complex
Chromatids of homologous chromosomes may break at a point of contact called what? (In prophase 1 of meiosis)
The chiasma
When chromatids of homologous chromosomes exchange equivalent pieces of DNA this process is called what?
Crossing over, can be a single or double crossover
What does mendels second law of independent assortment mean?
That the way genes are inherited for one trait doesn’t affect the inheritance of genes for other traits, as long as those genes are in difference chromosomes, genes of separate chromosomes are inherited independently and their combinations in offspring are random, leading to genetic diversity
In metaphase 1 of meiosis homologous pairs (tetrad) align at the metaphase plate, and each pair attached to a separate spindle fiber by what?
It’s kinetochore
What is the main difference between mitosis of metaphase and meiosis metaphase 1?
In mitosis each chromosome is lined up on the metaphase plate by 2 spindle fibers (1 from each pole); in meiosis homologous chromosomes are held by 1 spindle fiber and are lined up across from each other at the metaphase plate
In anaphase 1 of meiosis homologous pairs seperate and are pulled to opposite poles of the cell in a process called?
Disjunction - accounts for mendels first law of segregation
What happened to each chromosomes in disjunction?
During disjunction each chromosomes of paternal origin seperates from its homologue of maternal origin, and either chromosomes can end up in either daughter cell
Separating of the 2 homologous chromosomes is referred to as…
Segregation
When do cells become haploid in meiosis?
Telophase 1
Between meiosis 1 and meiosis 2 there may be a short rest period called what?
Interkinesis, in which the chromosomes partially uncoil
What is meiosis 2 very similar with? And why
Mitosis because sister chromatids are separated from each other in both
What follows telophase?
Cytokinesis
After completion of meiosis 2 up to how many haploid daughter cells are produced per gametocyte?
4
It mitosis and meiosis they both start with 2n and go to?
Mitosis: 2n - 2n
Meiosis: 2n - n
What cells does mitosis and meiosis occur in?
Mitosis: in all dividing cells
Meiosis : only in sex cells
