Chapter 10 Flashcards
What type of cell division occurs in bacteria?
Binary fission
Ploidy
the number of set of chromosomes an organisms has
Haploid (n)
one complete set of chromosomes
Diploid (2n)
total number of chromosomes in a cell
How many chromosomes in a haploid cell?
23
How many chromosomes in a diploid cell?
46
Homologous
a pair of the same kind of chromosome in a diploid cell
Homologue
Karyotype
particular array of chromosomes an organism possesses
What are chromosomes composed of?
Chromatin
Heterochromatin
Inactive domains of chromatin
Euchromatin
active domains of chromatin
Nucleosome
complex consisting of a DNA duplex would around a core of eight histone proteins
What is the nucleosome composed of?
DNA and histone proteins
Histone proteins have a ______ charge, which are strongly attracted to _______ charged DNA
+, -
What are four histones contained in nucleosomes?
H2A, H2B, H3, H4
The primary histones (H2A, H2B, H3, H4) associate together to form a _________________.
histone octamer complex
Condensin and cohesin are both examples of
SMC proteins
Cohesin
protein complex that holds sister chromatids together
Condensation/decondensation
How tightly chromosomes are wound depends of the phase of the cell cycle
Why would chromosomes be decondensed?
To express genes
Why would chromosomes be condensed?
to separate during cell division
Condensation is controlled by the protein _____.
condensin
Sister chromatids
Two replicas of a single chromosomes
What are the five phases of the cell cycle?
G1, S, G2, M, cytokinesis
G1 (gas phase 1)
primary growth phase of cell
S (synthesis)
genome is duplicated
G2 (gap phase 2)
organelles replicate, microtubules organize
Mitosis
spindle apparatus assembles, bind to chromosomes, and moves sister chromatids apart
What are the five phases of mitosis?
- Prophase
- Prometaphase
- Metaphase
- Anaphase
- Telophase
Cytokinesis
cytoplasm divides, creating two daughter cells
Mitosis and cytokinesis make up the __________
M phase
_______ and ________ make up the M phase
Mitosis; cytokinesis
How long is the cell cycle in typical mammal cells?
24 hours
How long is the cell cycle in human embryos?
20 minutes
How long is the cell cycle in human liver cells?
More than a year
What types of cells remain in G0 phase permanently?
Muscle and nerve cells
What occurs in S (synthesis) phase?
- Cell’s DNA is replicated
- Each chromosomes replicates to produce two sister chromatids
Cohesion proteins
hold centromeres of two sister chromatids together
Where do microtubules attach?
Kinetochore
What occurs during G2 phase?
- chromosomes begin to condense
- extensive synthesis of tubulin
Tubulin
protein to make microtubules
Prophase
The condensed chromosomes become visible
The nuclear envelope breaks down.
The assembly of the spindle takes place
Spindle apparatus
assembly that carries out separation of chromosomes during cell division
What is the spindle apparatus made up of?
Centrosomes (Centrioles) and Microtubules
What structure separates sister chromatids during prophase?
Spindle apparatus
What events occur during prophase?
- Chromosomes condense and become visible
- Cytoskeleton is disassembled
- Golgi and ER are dispersed
- Nuclear envelope breaks down
What events occur during prometaphase?
- Kinetochores attach condensed chromosomes to spindle
- Microtubules pull sister chromatids to equator of the cell
What evens occur during metaphase?
- Chromosomes align in center of the cell
Metaphase plate
imaginary plane through the equator of the cell
What is the shortest phase in mitosis?
Anaphase
What events occur during anaphase?
- Proteins holding sister chromatids together at centromere are removed
- Sister chromatids move apart toward poles
Anaphase A
- kinetochores are pulled toward the poles
- microtubules connecting kinetochores shorten
- tubulin subunits are removed
Anaphase B
- poles move apart
- microtubules slide past each other towards the poles
- physically elongate cell
What events occur during telophase?
- spindle apparatus disassembles
- nuclear envelope forms around each set of sister chromatids
What phase in mitosis is the reversal of the process of prophase?
Telophase
The cleavage furrow is composed of _____________
actin filaments
A cell plate forms partitioning the daughter cells by fusing with the
plasma membrane
Formation of cell plate
Cellulose is laid down on the new membranes = two new cell walls
The space between the two cell walls become the middle lamella
What are two irreversible steps in the cell cycle?
- duplication of the genome (G2 phase)
- Separation of sister chromatids (anaphase)
Cyclin-dependent kinase (Cdk)
protein kinase enzyme only active when complexed with cyclin
Cyclin
regulatory protein required to activate Cdk
How does MPF control the cell cycle?
- Cyclins accumulate in G2 and associate with MPF -> initiates mitosis
- MPF contributes to breaking up nuclear envelope (prometaphase)
- MPF is involved in chromosome condensation and spindle formation (prophase)
g1/s checkpoint
primary checkpoint where cell decides to divide or not
The ______ checkpoint is most susceptible to external signals
G1/S
What would halt the cell cycle at the g1/s checkpoint?
- damage to DNA
- starvation conditions
- lack of growth factors
g2/m checkpoint
- stimulates mitosis to start
- assesses success of DNA replication
- stalls cycle if DNA has not been accurately replicated
Spindle checkpoint
ensures all chromosomes are attached to spindle in preparation for anaphase
Anaphase promoting complex (APC)
sends the signal that all chromosomes are aligned properly at metaphase plate
What is the function of the APC?
Trigger anaphase
What are the two main functions of APC?
- Activates protease - destroys cohesion proteins holding sister chromatids together
- Necessary for destruction of mitotic cyclins to drive cell out of mitosis
Cells stop at g1/s checkpoint if they are deprived of ___________
growth factors
Describe the characteristics of binary fission.
Like the cell cycle – two new daughter cells are produced
Each have identical genomes
Most bacteria have a single circular chromosome
occurs much faster than eukaryotic cell division
less DNA is broken down
Which ‘events’ in the cell cycle are considered irreversible?
Duplication of genome
Separation of sister chromatids
t or f: Duplication of the genome occurs prior to M-Phase
true
_________ activates MPF.
Cyclin
Match the following events with the correct phase of Mitosis.
Interphase:
- Genome duplicates
- The G1/S checkpoint
- Chromosomes begin to condense
Prophase:
- The spindle apparatus begins to form
- Nuclear envelope degrades
Metaphase:
- Sister chromatids align on the metaphase plate
Anaphase:
- Sister chromatids pull apart
- Cells poles begin to pull apart
Telophase:
- Nuclear envelope reforms
T or F: Two attached sister chromatids are considered a single chromosome.
True
Why is it necessary for the nuclear envelope to be disassembled early in mitosis?
To allow microtubules to attach to the sister chromatids