Midterm 2 pt.2 Flashcards
Prokaryotes vs eukaryotes?
Prokaryotes: a single circular chromosome
Eukaryotes: multiple linear chromosomes
genome?
complete genetic material of an organism (DNA) or virus (RNA), the genome is duplicated before cell division.
The DNA is wound…
twice around a protein core
What do chromosones consist of?
1 centromere: region on each sister chromatid where sister chromatids attach to each other
2 chromatids: identical copies of the same original chromosome joined all along their lengths by protein complexes
Phases of mitosis? (5)
prophase, prometaphase, metaphase, anaphase
telophase
G2 phase of interphase? mitosis
Presence of the nuclear envelope and one or more nucleoli
Centrosome duplication into 2 centrosomes
Chromosomes, duplicated during S phase are not condensed
Prophase of mitosis?
chromatin fibers condensing into chromosomes
nucleoli disappear.
Each duplicated chromosome appears as two identical sister chromatids
The mitotic spindle begins to form
The centrosomes move away from each other
Prometaphase of Mitosis?
nuclear envelope fragments.
microtubules extending from centrosome invade the nuclear area
kinetochore, a specialized protein structure has formed at the centromere of each chromatid
microtubules attach to the kinetochores
Microtubules not attached to the kinetochores interact with the microtubules from the opposite pole
Metaphase of Mitosis?
The centrosomes are at opposite poles of the cell.
The chromosomes have reached the metaphase plate chromosomes’ centromeres lie at the metaphase plate.
Anaphase of Mitosis?
Cohesins that bind sister chromatids are cleaved by a separate protein
Each chromatid now becomes a distinct chromosome.
daughter chromosomes move toward opposite ends of the cell
At the end of anaphase, the two ends of the cell have equivalent and complete collections of chromosomes.
Telophase of mitosis?
Two daughter nuclei form in the cell. Nuclear envelopes arise from the fragments of the parent cell’s nuclear envelope
Nucleoli reappear, chromosomes become less condensed.
Any remaining spindle microtubules are depolymerized.
Cytokinesis
Formation of a cleavage furrow, which pinches the cell in two
cytokinesis in plants?
The division of the cytoplasm is initiated during the late telophase and involves the alignment of vesicles to form a central plate (phragmoplast). These vesicles can reconstitute a cell wall.
Binary fission in prokaryotes? 4 steps
- Cell division is initiated when the DNA of the bacterial chromosome begins to replicate at the origin of replication, producing two origins.
- One origin moves toward the opposite end of the cell.
- The cell elongates and double in size.
- Replication ends and the plasma membrane pinches inward
Phases of the cell cycle?
Interphase (including G1, S, and G2 subphases): 90% of the cycle
M phase (including mitosis and cytokinesis): 10% of the cycle
S and G phases?
G1/ G2 phase ): metabolically active cell growth
S phase (“synthesis”): duplication of the chromosomes
3 checkpoints for regulation of cell cycle?
G1, G2, M phase
Two types of regulatory molecules?
Cyclins: proteins whose concentration fluctuate and that bind to specific kinases
Cyclin-dependent kinases : activate other proteins through phosphorylation and using ATP
What are MPFs?
The Cdk-cyclin constitutes a maturation promoting factor (MPF) that peaks during the M phase. MPF is a protein that triggers the cell’s passage from the G2 checkpoint into the M phase
How do MPFs regulate the signalling pathway? 3
Fragmentation of the nuclear envelope
Chromosome condensation
Spindle formation
G1 and S, G2, M checkpoints
G1 checkpoint:
Abundance of resources before proceeding to S, G2 and M
Failure leads to the G0 phase
M phase checkpoint:
Activation of protein complexes that cleaves cohesins
RAS protein?
G protein that relays a signal from a growth factor
Cellular response: synthesis of a protein that stimulates the cell cycle
Proto-oncogene: gene coding for a protein that stimulates the normal cell growth and division
p53 gene?
tumor-suppressor gene, activated when there is damage to the cell’s DNA.
Cellular response: The cell cycle is halted until the damage has been repaired
Tumor-suppressor gene: gene coding for a protein that inhibits the cell cycle and cell division
Apoptosis?
programmed cell death. Important process that removes damaged or unnecessary cells and is initiated when a cell is damaged, superfluous, or potentially dangerous to an organism
Apoptosis activates?
Activation of…
proteases: enzymes that attack and digests proteins
nucleases: enzymes that attack and digests nucleic acids.
What is Meiosis?
type of cell division in sexually reproducing organisms consisting of two rounds of cell division.
Meiosis produces 4 daughter cells, each with half the number of chromosome sets as the original cell
Fertilization brings this number back to to the original number
Prophase 1 meiosis?
Chromosome condensation, centrosome movement, spindle formation, and nuclear envelope breakdown
each chromosome pairs with its homologue , and crossing over occurs
Each homologous pair has one or more X-shaped regions called chiasmata
microtubules from the poles attach to the two kinetochores, at the centromeres.
Metaphase 1 meiosis?
Pairs of homologous chromosomes are arranged at the metaphase plate.
Both chromatids of one homologue are attached to kinetochore microtubules from one pole
Anaphase 1 meiosis?
Breakdown of cohesins, allowing homologues to separate.
The homologues move toward opposite poles
Sister chromatid cohesion persists at the centromere, causing chromatids to move as a unit
Telophase 1 cytokensis meiosis?
Each half of the cell has a complete haploid set of duplicated chromosomes
Cytokinesis is initiated , forming two haploid daughter cells.
Prophase 2 meiosis?
Duplication of the centrosomes and formation of a spindle apparatus
Chromosomes , move toward the metaphase II plate
Metaphase 2 meiosis?
two sister chromatids of each chromosome are not genetically identical.
The kinetochores of sister chromatids are attached to microtubules extending from opposite poles.
Anaphase 2 meiosis?
Breakdown of cohesins that hold the sister chromatids together at the centromere, allowing the chromatids to separate.
Chromatids separate and move toward opposite poles as individual chromosomes
Telophase 2 and Cytokinesis?
Nuclei form, the chromosomes begin decondensing, and cytokinesis occurs.
Intra-chromosomal recombination?
crossing over during the prophase I of meiosis produces recombinant chromosomes
Crossing overs contribute to much of the genetic variation within a population of organisms
Synapsis?
pairing and physical connection of duplicated homologous chromosomes during
prophase I of meiosis
