7: mitosis/meiosis/cell cycle Flashcards
Bacterial DNA replication
Single, uncoiled ring of DNA replicates away from the origin in both directions until all of the DNA is copied. DNA is also stored in plasmids.
Centromere (def. & number)
Platform in the middle of a (duplicated) chromosome where sister chromatids are most tightly connected and where the kinetochores are built; 1 centromere per chromatid, so 2 per duplicated chromosome
Kinetochore (def. & number)
Protein complex built on the centromere where microtubules connect during anaphase; 1 kinetochore per chromatid, so 2 per duplicated chromosome
Chromatin
Stack of nucleosomes (which are DNA + histones)
Nucleosome
DNA coiled around a histone
Chromatid
Made of chromatin
Cell specialization due to
The way DNA strands are wrapped around histones (which sections of genes are accessible and therefore code for things, and which sections aren’t)
Stages of interphase
1) G1 - Cell grows more organelles (except mitochondria/chloroplasts) and cytoplasm, as well as cell membrane
2) S - DNA replicates to prepare for division’
3) G2 - Chloroplast and mitochondria replicate, DNA condenses into chromosomes, and microtubules are synthesized
3 checkpoints
Mitotic/metaphase/spindle checkpoint
G1/S checkpoint
G2/M checkpoint
Mitotic/metaphase/spindle checkpoint
Assesses whether microtubules are properly attached to kinetochores of sister chromatids; allows cell to go from metaphase to anaphase if passed. If it is not passed, the cell will delay anaphase until all kinetochores are attached to microtubules.
G1/S checkpoint
Assesses the V/SA ratio, nutritional state, and local cell density (contact inhibition) - if they are sufficient, the DNA will replicate and the cell will prepare to divide. If something is wrong, the cell will enter G0 and may stay there permanently or may enter G1 again when conditions improve.
G2/M checkpoint
Assesses whether the DNA (from S) has been replicated correctly before the cell undergoes mitosis. If the DNA is damaged, the p53 (a tumor suppressor) gene can repair the DNA or cause apoptosis. If the DNA is correct, the cell will enter mitosis.
Centrioles
2 organelles that are found in the centrosome
Centrosomes
Organelles that organize and produce microtubules, which attach to chromosomes/chromatids (depending on meiosis/mitosis). They also migrate to opposite poles of the cells to lengthen it.
Mitotic spindle
Made of microtubules and proteins (taken from the disassembling of the cytoskeleton), specifically tubulin subunits, which allow the microtubules to shorten / lengthen
Embryonic cells
Divide as quickly as possible
Oncogenes
Genes that code for proteins that stimulate cell division. They are needed in a cell, but after a certain extent, they should be turned off to prevent cancer. If they are constantly on, malignant tumors will form.
Tumor suppressor genes
Genes that code for proteins that suppress cell division. They are also needed in a cell, but they need to be turned on. When they fail to be turned on, the risk of cancer greatly increases.
Kinase def, Cyclin-dependent kinases (Cdks), and types of cyclins
A kinase is an enzyme that speeds up chemical reactions by phosphorylating substrates. A cyclin-dependent kinase is an enzyme that requires cyclin (a protein) in order to be activated.
There are different types of cyclins (ie, G1 cyclin, mitotic cyclin), and when a certain cyclin binds with the Cdk, it activates the Cdk, but it also directs the Cdk to catalyze a certain set of proteins. These proteins allow the physiological processes of different cell cycle stages to happen. So, ie, when mitotic cyclin binds w/ Cdk, it will cause Cdk to phosphorylate proteins that make the nuclear membrane break down.
Prophase (mitosis) and prometaphase
Prophase:
- DNA condenses into chromosomes
- There is no longer a nucleolus
- Sister chromatids are visible
- Mitotic spindle begins to form (made up of centrosomes + microtubules)
- Centrosomes begin migrating away from each other
Prometaphase:
- Nuclear envelope is completely gone
- Some microtubules start attaching to chromosomes (at kinetochores)
Metaphase (mitosis)
- Centrosomes are at opposite poles
- Chromosomes align at metaphase plate
- A microtubule is attached to each kinetochore
Anaphase (mitosis)
- Sister chromatids are pulled away from each other; each chromatid is now its own chromosome
- Cell continues to elongate
Telophase (mitosis)
- Nucleus begins re-forming
- Chromosomes decondense
Cell regulators for the cell cycle are found in the __
Cytoplasm (during the S or M phase)
Cyclin levels / processes throughout cell cycle
1) Cyclin is produced and accumulates from S through G2.
2) At the end of G2, Cdk and cyclin combine to form MPF. When enough MPF is formed, the cell passes the G2 checkpoint and enters mitosis.
3) As long as the cyclin and Cdk are bound, mitosis will continue. This means that in order for mitosis to stop, the cyclin is degraded in anaphase, allowing the cell to stop mitosis and the daughter cells to enter G1.
4) During G1, cyclin is broken down. Cdk is recycled because enzymes are reusable.
5) Cyclin is synthesized again in the late S phase.
Growth factor
A protein released by a certain cell into the extracellular space that causes other cells to divide
Transformation
A cell in culture develops the ability to divide indefinitely (like a cancer cell)
Prophase I (meiosis)
- DNA condenses into chromosomes
- Homologous chromosomes line up so that synapsis and crossing over can occur
- Each homologous chromosome is attached to 1 microtubule
Metaphase I (meiosis)
- Homologous chromosomes align at metaphase plate
- The orientation of each pair of chromosomes (in regards to which chromosome is positioned toward which pole) is random
- Independent assortment occurs here
Anaphase I (meiosis)
Homologous pairs are pulled away from each other to opposite poles of the cell. Sister chromatids of each chromosome remain attached to each other.
Telophase I (meiosis)
Chromosomes arrive at opposite poles of the cell. Cytokinesis overlaps and gives rise to 2 daughter cells. This is when the cell goes from diploid to haploid.
Meiosis I and II products
Meiosis I - produces haploid cells (from diploid -> haploid) that aren’t gametes
Meiosis II - produces haploid cells from haploid cells (are gametes)
