Module 11 (DNA Replication and Cell Division) Flashcards
Why does cell division occur?
Cell growth
Cell replacement
Cell healing
Cell reproduction
How can a cell make more cells?
Using the process known as cell division
Requirements of cell division
- The parent cell must be big enough to divide (so the daughter cells get enough cytoplasmic components)
- The two daughter cells must each receive all of the genetic material from the parent cell
How do prokaryotic cells divide?
Using binary fission
Steps of Binary Fission
Protein bind circular DNA to inner membrane
DNA replication travels bidirectionally
The new circular DNA is also attached to the inner membrane
Cell elongates, and starts to pinch at middle of cell
New cell membrane and cell wall separates the daughter cells
Genome
Genetic material of an organism
Mitochondrial genome
Maternally inherited
Is there a correlation between genome size and organismal complexity?
No! There is no correlation. An amoeba has 670000kb, but a human has 3100kb
Nucleoid
Loops of circular DNA, coiled around itself, bound together by proteins
Chromatin
Nucleosomes packaged together, forms a strand (about 30nm in diameter)
Nucleosomes
DNA is wrapped around histone proteins twice (10nm in diameter)
Coiled chromatin fiber
Chromatin fiber is further coiled (300nm)
Coiled coil
The coiled chromatin fiber is coiled further (700nm)
Chromatid
Only visible in cells that are about to divide, made from coiled coils (1400nm)
Stem cells
Undifferentiated cell that can undergo unlimited amounts of cell division and differentiate into any of the specialized cells (found in bone marrow when talking about blood cells)
Somatic cells
Nonrepoductive cell, most common type of cell (normal)
Germ cells
Reproductive cells that produce gametes (eggs or sperm)
The time when the parent cell divides into two daughter cells
M phase
How does cell division occur in eukaryotes?
Through the cell cycle
The time between two successive M phases is known as…
Interphase
Cytokinesis
The division of the cytoplasm into two daughter cells
Mitosis
Separation of replicated chromosomes
How long does interphase usually last between two M phases?
Around 10-14 hours
Cell’s preparations before division
DNA replication in nucleus
Increasing the size of the cell
G1 phase
First stage in interphase
- increase cell size and protein content
- 1st gap phase
- Synthesis and activation of regulatory proteins
S phase
“Synthesis” phase, second phase in interphase
- DNA replication
G2 phase
Third phase of interphase
- Second “gap” phase
- Preparation for M phase
G0 phase
Separate from G1, no active preparation for cell division
- cells that do not divide (liver cells- hepatocytes)
What does it mean by “DNA replication is semiconservative”?
Each strand of parental DNA acts as a template strand for the synthesis of a daughter strand
One strand of DNA is ________, one strand is _________
One strand is old parental, one strand is newly synthesized
Replication Fork
The place where the two strands of DNA split from each other during replication
Helicase
Unwinds parental DNA at replication fork
Single-strand binding protein
Holds the single stranded regions of the parental strands to prevent them from coming back together.
Topoisomerase
Relieves the stress of unwinding the DNA, works upstream the replication fork
DNA Polymerase
Adds bases to nucleotide strand, requires four deoxyribonucleotides (dATP, dGTP, dCTP, dTTP)
- Only synthesize DNA in 5’-3’
- Can usually correct mistakes as it goes
- Needs an RNA primer
- Also removes RNA primers and replaces with DNA bases
RNA primase
Creates the RNA primer with the 3’ OH group that allows the DNA polymerase to start to synthesize the DNA
What is the purpose of the 3’OH group on the RNA primer?
It attacks the phosphate bond of the incoming nucleotide to initiate the synthesis
Leading strand
The strand that grows continuously toward the replication fork
Lagging strand
The strand that grows away from the replication fork, synthesized in segments
Okazaki fragments
The synthesized pieces of the lagging strand that are disconnected from each other
DNA ligase
Okazaki fragments are joined together after RNA primers have been replaced with DNA nucleotides
Trombone Model
As the DNA is being unwound, one strand is looped
How are DNA replication errors caught?
- DNA polymerase can detect mispairing of hydrogen bonding
- Removes incorrect nucleotide, and inserts correct one
Replication of circular DNA
Happens in most bacteria
- Single origin of replication, replication goes in both directions until they meet on the opposite side and fuse
Leading and lagging in circular DNA
Each replication fork has a leading strand and a lagging strand (two replication forks)
Linear DNA origins of replication
Eukaryotes have multiple origins of replication, multiple replication forks, and proceeds bidirectionally, when two replication bubbles meet, DNA ligase seals the gap in fragments
At the end of Linear DNA…
On the lagging strand, the primer is removed and leaves a section of template of DNA unreplicated, every time DNA is replicated one strand is shortened
Telomeres
End of chromosomes with repeated sequence, repeats thousands and thousands of times
Telomerase
Extends the ends of the chromosome by replacing missing nucleotides
- Ribonucleoprotein -> protein RNA complex
- Carries its own primer (template RNA)
- Reverse transcriptase activity
What types of cells is telomerase active
Stem cells
Germ cells (sex cells)
Hayflick limit
The maximum number of times that a cell can replicate before the telomeres become too short
About 50 times
Haploid
A cell with one copy of each chromosome
Diploid
A cell with two copies of each chromosome
Sister chromatids
Identical copies of chromosomes after DNA replication, held together at the centromere
Karyotype
A visual representation of one’s chromosomes
Mitosis
For somatic cells to duplicate
Stages of Mitosis
Prophase, Prometaphase, Metaphase, Anaphase, Telophase
Prophase
Chromosomes condense, cell assembles mitotic spindle, centrosomes duplicate and migrate to opposite poles
Prometaphase
Nuclear membrane breaks down, microtubules of grow and shrink looking for chromosomes (attach to them)
Kinetochores
Two protein complexes that a centromere is associated with, one on each side of centromere, site of attachment for microtubule
Metaphase
Mitotic spindle lengthens and shortens pushing chromosomes toward center of the cell
Metaphase plate
The plane approximately half way between the two poles of the spindle where the chromosomes line up
Mitotic spindle
Made of microtubules, pull chromosomes apart
Anaphase
Centromere divides and kinetochore microtubules shorten, pulls chromatids apart, one to each pole
Telophase
Complete set of chromosomes arrives at spindle pole, microtubules of mitotic spindle break down, nuclear envelopes form around each chromosome set, chromosomes decondense
Cytokinesis in animal cells
The division of the parent cell into two daughter cells
- Ring of actin filaments form around inner face of cell membrane, which contracts and pinches the cytoplasm, divides it
Contractile ring
Forms at the equator of the cell, ring of actin filaments, contracts to pinch the cytoplasm of the cell
Cytokinesis in plant cells
Forms phragmoplast in middle of cell during telophase, guide vesicles with cell-wall components to middle of the cell, vesicles fuse to form a new cell wall in the middle (late Anaphase and Telophase), which then fuses with original cell wall
Phragmoplast
Overlapping microtubules that guide vesicles containing cell-wall components to the middle of the cell in plant cells
Cell plate
The new cell wall formed by fused vesicles in the middle of the parent plant cell
Meiosis
Produce daughter cells with half as many chromosomes as the parental cell, source of variability, one round of DNA synthesis, two rounds of cell division
By the end of meiosis I
The homologous chromosomes separate
By the end of meiosis II
The sister chromatids separate
Meiosis I, Prophase I
Homologous chromosomes pair with each other, chiasma occurs
Synapsis
When homologous chromosomes pair with each other
Bivalent
Two pairs of sister chromatids (tetrad)
Chiasma
Crossing over of DNA segments, exchanging genetic information, random, also helps hold bivalents together
Meiosis I, Prometaphase I
Spindles attach to kinetochores on chromosomes
Meiosis I
Results in homologous chromosomes separated, haploid cells, reductional division (# of chromosomes are halved)
Meiosis II
Sister chromatids separate, results in gametes, equational division, Cells in meiosis II have the same # of chromosomes at the beginning and the end
Mitosis vs. Meiosis
Suggests that meiosis evolved from mitosis, common ancestor of eukaryotes
Cytoplasmic division in female gametes
One cell with most of the cytoplasm, three polar bodies with only small amounts of cytoplasm, only the large one is yielded
Oocyte
Female egg
Cytoplasmic division in male gametes
Equal cytoplasmic division, most of cytolasm is eliminated
Sperm meeting egg
Restores diploid state and increases genetic diversity
Initiation of DNA repliaction
G1/S transition
Initiation of mitosis
G2/M transition
How are is the cell cycle controlled?
Cyclic activity of proteins and kinase
What are the proteins and kinases that control the cell cycle?
Cyclins and cyclin-dependent kinases (CDK)
Cyclins
Regulatory protein subunits of specific protein kinases
CDKs
Kinases that phosphorylate other proteins whose actions are necessary for the cell cycle to progress (protein is active), only active when bound to cyclin
- Different types that act at different steps of the cell cycle
Cyclin D and Cyclin E
Levels increase in G1 phase, activates transcription factors that lead to expression of DNA polymerase
Cyclin A
Activates CDKs that initiate DNA synthesis during S phase
Cyclin B
Increases during G2 phase, activate CDKs that initiate the breakdown of nuclear envelope, formation of mitotic spindle
DNA damage checkpoint
Checks for damaged DNA before the S phase (for example, breaks in DNA strand)
DNA replication checkpoint
Checks for unreplicated DNA at the end of G2
Spindle assembly checkpoint
Checks that all chromosomes are attached to the spindle before the cell continues with mitosis
If DNA is damaged by radiation
Activates a protein kinase that phosphorylates the p53 protein, which activates the transcription of some genes, one blocks the activity of the G1/S cyclin-CDK complex, freezes the cell at the G1/S transition, cell is able to repair damage
p53 is often called…
The guardian of the genome
Phosphorylated p53 also…
Stimulates the production of bax protein, represses transcription of Bcl-2 protein, shift the overall concentrations of of them, creating Bax-bax dimers, creating apoptosis
Apoptosis
Increase of Bax-bax dimers causes programmed cell death
Apoptosis in embryotic development
Hands initially look like a paddle until cells are killed, creating digits
Uses of apoptosis
Maintenance of tissue size, elimiation of specific cells, elimination of genetically damaged cells
Cancerous cells
Unable to undergo apoptosis, uncontrolled cell division
Oncogenes
Cancer-causing genes first discovered in viruses
Proto-oncogenes
Normal genes important in cell division that have the potential to mutate into oncogenes
Tumour suppressor gene
Opposite of oncogenes, inhibit cell division, p53 protein is an example
Metastasis
When cancer cells invade tissues
Angiogenesis
The blood vessel formation caused by cancer cells
