Cell Bio: Cell Division and Cell Cycle Regulation

Asexual reproduction

a single cell gives rise to identical offspring or clones. genetic variation is due to mutations

advantages of asexual reproduction

1. faster

2. potentially safer

3. saves energy

4. no need for courtship or selection

examples of asexual reproduction

binary fission in prok and mitosis in euk

sexual reproduction

a new organism is created through the mixing of genetic material from two different cells/organisms

examples of sexual reproduction

meiosis in euk, shmooing yeast, pollination in plants, and bacterial conjucation

advantages of sexual reproduction

1. jhigh genetic variability (population diversity)

2. facilitates adaptation

3. accelerates evolution

mitosis

a type of somatic and germ cell division that results in 2 daughter cells each having the same number and kind of chromosomes as the parent cell (diploid)

-typical of ordinary tissue growth/development or regeneration (replacement of damaged cells)

meiosis

a special type of cell division of germ cells used to produce the gametes (sperm or eggs). it involves two rounds of division and ultimately results in 4 daughter cells with only one copy of each paternal and maternal chromosome (haploid)

g1 phase (gap 1)

the cell grows and prepared proteins for DNA replication

S phase (synthesis)

the cell duplicates its chromosomes

g2 phase (gap2)

the cell continues to increase cellular components and proteins for mitosis as well as performing normal cell functions

prophase

breakdown of nuclear membrane, spindle fibers appear, and chromosomes condense

metaphase

spindle fibers attach to chromosomes and chromosomes align at metaphase plate

anaphase

centromeres divide and sister chromatids move to opposite poles

telophase

nuclear membrane reforms, chromosomes decondense, and spindle fibers disappear

cytokinesis

cytoplasm divides

G1 checkpoint

check to see if the cell is ready to divide: is it big enough, is there enough energy and other reserves, is the DNA damaged; if not, cell goes to G0 until it is ready to divide

G2 checkpoint

check to see if dna replication is correct, if DNA is damaged, and if cell size is good

M checkpoint

checks for chromosomal alignment on metaphase plate and if they are ready to be pulled apart

two types of regulatory proteins which are involved in cell cycle progression

cyclins and cyclin-dependent kinases (Cdks)

the activity of Cdk rises and falls with changes in what?

concentration of its cyclin partner

the activated Cdks provide the ____ to progress through the checkpoints through phosphorylation events

go-ahead phase

activation of Cdks is dependent upon what?

a variety of proteins at each checkpoint

proto-oncogenes

make proteins that stimulate cell division

tumor supressor genes

make proteins that inhibit cell division or cause apoptosis

two major classes of genes that regulate the cell cycle

proto-oncogenes and tumor suppressor genes

proto-oncogenes

act like gas pedals promoting cell division

-if modifications or mutations occur to _______, they become activated oncogenes and can result in runaway cell growth.

-oncogenes are highly prevalent in cancers and often result in modified levels of growth factors, growth factor receptos, signal transduction molecules, and transcription factors

tumor suppressor genes (TSGs)

act like brake pedals inhibiting cell divition

-if mutations or modifications occur to inactivate _______, they can result in runaway cell growth

-mutant _____ are quite common in cancers

potential causes of tumor suppressor deregulation

1. point mutations in the gene

2. hypermethylation of the promoter

3. deletions and aneuploidies

restriction point

the G1/S checkpoint is a very important one as it represents a stage to pause the cell in clycle G0

what do rising levels of Cyclin D and E at the G1/S checkpoint result in?

binding to a Cdk which phosphorylates a tumor suppressor gene called a retinoblastoma protein (pRb)

retinoblastoma protein (pRb)

normally represses the transcription of genes by binding transcription factors involved in progression to S phase

-upon phosphorylation, pRb becomes inactive and the cell can progress forward

Which proteins control the rapid changes in levels of the cyclin proteins to promote cell cycle progression?

ubiquitin ligases

p53

the master regulator for cell cycle repair

-a tumor suppressor gene that helps the cell pause the cell cycle and promote the appropriate response

p53 is normally ubiquitinated by a protein called _____ and degraded by the proteasome

Mdm2 (ubiquitin protein ligase)

When cell damage occurs…

kinases phosphorylate p53 which prevents ubiquitination and subsequent destruction

nondisjuction

a process where the chromosomes of the cell do not separate during anaphase

aneuploidy

cells that receive the incorrect chromosome number

-two main types in humans are monosomy and trisomy