Questions # 8 Flashcards
October 17-22
What is the cell cycle?
The repeating sequence of growth and division through which cells pass each each generation.
What are the two main problems cells need to solve in order to divide, and which is more important?
- Make sure there is two times as much cytoplasm, organelles, ect.
- Make sure daughter cells get exact copy of genome.
How do prokaryotic cells divide?
Binary fission
How do prokaryotes know when they have finished replicating their genomes?
Two replication complexes meet on opposite sides of origin of replication (terminus of replication)
Where do bacteria add new cell wall and plasma membranes as they grow?
Between mesosomes
How do prokaryotes ensure that each cell gets a copy of the genome after cell division?
Plasma memvran pinches between mesosomes; cell wall forms between mesosomes.
How do eukaryotic cells divide?
Mitosis (growth, repair, replace)
Why is cell division more complicated in eukaryotic cells than prokaryotic cells?
Genome is larger and organelles must be replicated.
why is there some much protein associated with DNA in eukaryotes?
Organizes and compresses DNA (histones)
What is chromatin, and and what is the difference between heterochromatin and euchromatin?
Chromatin: state of chromosomes when they are thin and spread out in the nucleus during interphase.
Euchromatin: open book
Heterochromatin: closed book
What are histones?
Positively charged proteins which DNA wraps around and neutralizes causing it to condense and organize.
What are nucleosomes, and what is their function?
fundamental packing unit of DNA which compresses DNA. This octamer histone core is made up of two H2A, H2B, H3, H4
How can our cells compress 2 meters of DNA into a nucleus less than um long
Dna–>(histone)–>nucleosome–>solenoids–>extended section chromosome–>cordinoid loop–>metaphase chromosome
(six nucleosomes= solenoid)
What are the conventional five levels of compression, and why is it controversial?
- nucleosome
- solenoid
- extended section chromosome
- condensed loop
- metaphase chromosome
What are chromosomes?
Structure in which genetic material is stored and transmitted to next generation composed of histones and DNA.
What are homologous chromosomes?
similar copies of some DNA molecule; get one from mom and one from dad
What are sister chromatids, and how do they differ from homologous chromosomes?
Sister chromatids are identical copies of the same DNA molecule
Homologous chromosomes are similar copies of the same DNA
What are centromere
site where sister chromatids are attached…until anaphase.
What is a kinetochore?
Protein attached to centromere to which microtubules attach.
What is a karyotype and why is it useful?
- array of individual’s chromosomes
- can be used to detect genetic defects, aneuploidy, and cancer
What is ploidy?
Number of homologous chromosomes
2n diploid two copies of each chromosome
1n haploid one copy of each chromosome (ie. gametes)
What are the two stages and five divisions of the eukaryotic cell cycle?
Interphase/Cell division
G1 Mitosis
S Cytokinesis
G2
What are the three divisions of interphase and what happens in each?
G1 -primary growth phase -longest phase -follows cytokinesis -make more cell organelles -determine if conditions favor cell division (spf checkpoint) S -DNA synthesis G2 -quality control -no DNA damage? conditions ok to divide? (mf check point) -chromosomes begin to condense -cells start building mitotic apparatus
What are the four phases of mitosis and what happens during each?
Prophase -chromosomes condense -mitotic apparatus forms -centrioles migrate to poles -nuclear membrane dissolves -microtubules attach to kinetochore Metaphase -chromosomes in center -cell checks that spindle is connected to kinetochores *M checkpoint Anaphase -chromatids pulled to opposite sides of cell Telophase -nuclei reforms -chromosomes decondense -mitotic apparatus disassembled Cytokinesis -division of cytoplasm (ring of actin at cleave furrow;vesicles form making cell plate)
How are chromosomes lined up on the metaphase plate?
Microtubules pull chromosomes back and forth between asters
What holds the sister chromatids together during metaphase.
Centromere
How are the chromosomes separated during anaphase?
Microtubules shorten and pull sister chromatids apart.
What is the difference between mitosis and cytokinesis and how do we know they are separate processes.
Mitosis
division of nucleus and distribution of chromosomes
Cytokinesis
division of cytoplasm
How do animals perform cytokinesis and hoe do plant cells perform cytokinesis?
Animal cells - cleavage furrow (actin ring)
Plant cells - (vesicles line up) phragoplast
What are the main differences between cell division in plants and animals?
- During cytokinesis
animal: cleave furrow
plant: cell plate - animal: microtubules pull against asters/centrioles
plant: anastral microtubules pull against cell wall.
Why don’t plants need asters?
Use cell wall to push against.
How do eukaryotes regulate cell division?
- cell progresses through a series of checkpoints
- check, read to continue?
- G1, G2, metaphase
Which checkpoint is most important and why is it most important?
G1 is most important
- asses if conditions are right
- want to copy DNA until ready (S phase follows G1)
What is MPF (mitosis promoting factor) and what does it do?
-controls G2; made during G2
-enzyme with two subunits
-catalytic subunit CDK (cyclin-dependent kinase) regulatory unit is cyclin.
(Kinase means add phosphate)
- promotes mitosis
- phosphorylates proteins, especially nuclear lamin, which causes nuclear membrane to break down; condenses chromosomes assembles mitotic apparatus (spindle)
- activated by sensors for growth factor amount of food; inhibited by DNA damage.
What are cyclins and what do they do?
Regulates the cell cycle.
- determine what CDKs (enzyme) will act on and how active it will be
- different cyclins are made at different times; have to be attached to CDK for CDK to work.
What are cyclin dependent kinases and what do they do?
- regulated by cyclin
- enzyme that phosphorylates its substrate … a kinase
- only active with a bound cyclin which determines what the enzyme will do
- important in regulating the cell cycle.
How does SPF sense i f the cell is ready to enter S and how does it then initiate the transition to S?
Synthesis Promoting Factor
CDK + a different cyclin
made in G1
-activated by a varietyof sensors
food, DNA, ready, cell large enough?
3 hr time lagHow does MPF sense if the cell is ready to divide, and how does it then initiate the transition to M?
MPF is activated by sensors for growth factors and amount of food. It is inhibited by DNA damage.
How is the metaphase check point regulated?
- are all chromosomes on metaphase plate?
- does each kinetochore have a spindle fiber?
- checked by pulling chromosome back and forth
What is APC and what does it do?
-anaphase promoting complex
-APC is inactive until all kinetochores are bound to microtubules
-triggers anaphase; sister chromatids separate as microtubules shorten.
(APC destroys securin destroys cohesin which holds chromatids to separate.)
Why must MPF be destroyed for cells to exit mitosis.
MPF keeps cell in mitosis.
How do multicellular organisms regulate cell division ?
- rely on presence of growth factor at cell surface receptor
- sets off phosphorylation cascade that activates SPF; result is passing start
