DNA & Replication Flashcards
Ch. 12, 16
What is the cell cycle
Life of a cell from the time of formation to its own division into 2 daughter cells
What is a genome
The totality of an organisms DNA
What is cohesin
Cohesin is a multi-protein complex that mediates cohesion between replicated sister chromatids (like a binder ring between sister chromatids)
What is a gamete
A reproductive cell with half as many chromosomes
When do chromosomes condense
After DNA replication
What is a centromere
The region of repetitive sequences in DNA where sister chromatids are connected
The “waist” of a duplicated chromosome
Define mitosis
Division of genetic material in the nucleus of a cell
*Not cell division
Define cytokinesis
Division of cell into 2 daughter cells
What are each of the following phases in cell division
1. G1
2. S
3. G2
4. M
5. Cytokinesis
- G1 = growth
- S = DNA replication
- G2 growth
- M = distribution of daughter chromosomes into 2 daughter nuclei
- Cytokinesis = division of cytoplasm into 2 daughter cells
What are 3 main properties of prophase
- Chromosomes condense
- Nucleoli disappear
- Miotic spindles begin to form
What are 3 main properties of prometaphase
- Nuclear envelop begins to fragment
- Microtubules extend from centrosome
- Kinetochores form at centromeres
What are 3 main properties of metaphase
- Centrosomes can now be found at opposite poles of cell
- Chromosomes have moved to metaphase plate
- Microtubules attach to kinetochores
What are 3 main properties of anaphase
- Sister chromatids separate
- Kinetochore tubules shorten at centrosome end
- Cell elongates as nonkinetochore mictotubules lengthen
What are 3 main properties of telophase
- Two daughter nuclei form in the cell
- Nuclear envelop arise from fragments
- Nucleoli reappear and chromosomes uncoil
What is the 1 main property of cytokinesis
- Formation of cleavage furrow
Where does spindle microtubule assembly occur
Centrosome
What is a centrosome
A subcellular region containing materials that function throughout the cell cycle to organize microtubules
Where are the centrioles located
The center of the centrosome
What happens to the centrosomes during the cell cycle
Interphase = Centrosomes duplicate
Prophase = Centrosomes move apart
Prometaphase = Spindle microtubules begin to grown out of Centrisomes
What is an aster
An array of short microtububles that extend from the centrosomes
What is a kinetochore
A protein structure at chromosome centromere that binds with kinetochore microtubules during prometaphase
What is the metaphase plate
The imaginary line where chromosomes align in the cell during metaphase
What is separase
An enzyme that separates sister chromatids
How does cytokinesis occur
With help from vesicles that come from the golgi
These vesicles move along microtubules to the middle of the cell (aka cell plate). The materials in the vesicles are used and the cell wall grows until a new plasma membrane arises from vesicles
How does binary fission work
- 1 OR moves to opposite side of cell. Chromosome replication begins at the origin of replications (OR).
- Cell elongates
- Replication finishes and plasma membrane is pinched inward until 2 cells are produced
What are cell cycle checkpoints
Stop and go signals that regulate the cell cycle
What is a maturation promotion factor
A.k.a. M-phase promotion factor
A cyclin-Cdk complex which regulated the passage of a cell from the G2 phase to the M phase
Explain how cyclin and Cdk levels rise and fall in regards to the cell cycle
Cyclin levels begin to rise during S phase and fall abruptly during anaphase. Cyclins associate with Cdk at the end of G2 phase, activating MPF which phosphorylates certain proteins that trigger mitosis. During anaphase, MPF switches itself off by destructing cyclin. Noncyclin Cdk remains in cell, inactive.
What is the G1 checkpoint
Signals continuation of G1, S, G2 phases. If no signal present, cell switches to G0 phase (non-dividing existance). Cells may come back from G0 phase
What is the G2 checkpoint
This checkpoint prevents damaged DNA from entering mitosis
What is the M checkpoint
This checkpoint determines if all chromatids are correctly attached to spindle microtubules
What is a growth factor
An outside signal from another cell that stimulates cell to divide
What is density-dependant inhibition
Cells can divide until they come into contact with one another
What is anchorage dependence
Cells require a substranum to attach to before they can divide
What is transformation in terms of DNA
a change in genotype and phenotype due to assimilation of external DNA by a cell
What is a bacteriophage
A bacteria eater
What is a virus
DNA/RNA enclosed by a protective protein layer which must infect a cell and take over metabolic machinery
What are Chargaff’s rules for DNA
- DNA composition varies between species
- For each species, the % of adenine and thymine bases are roughly equal, as are those of cytosine and guanine*
*This was realized later to be exact
What does antiparallel mean
subunits run in opposite direction
What molecular group is attached to the 5’ end of a deoxyribose
Phosphate group
Which molecular group is attached to the 3’ end of a deoxyribose
OH- group
Which molecular group is attached to the 1’ end of a deoxyribose
Nitrogenous base
What defines a purine nitrogenous base and which bases are purines
Purines are nitrogenous bases with 2 organic rings. These bases are adenine and guanine
What defines a pyrimidine nitrogenous base and which bases are pyrimidines
Pyrimidines are nitrogenous bases with a single organic ring. These include thymine, cytosine, and uracil
Why is it important that each nuclear base pair has 1 purine and 1 pyrimidine
This assures the double helix will fit properly; if there are 2 purines, the helix will be too wide, while 2 pyrimidines would be too narrow
What is the semi-conservative model
When a double helix of DNA replicates, each of the two daughter cells will have one old strand and one new strand
What is an origin of replication
(Origin of replication will be referred to as OR)
A short stretch of DNA with a specific nucleotide sequence where replication of DNA will begin
What is the replication bubble
The space between 2 separated DNA strands at the OR
What is the replication fork
A Y-shaped region where parental DNA strands are unwinded
Found at the end of a replication bubble
In what direction does DNA replication occur
5’ → 3’ direction
What are the leading and lagging strands in DNA replication
The leading strand goes in the 5’→3’ direction* while the lagging strand is read 3’→5’ which accounts for okazaki fragments
*Seen on the right side of the OR in the rep. bubble; read right - left
What is the first step in DNA replication
Step 1/7
Helicase will unwind the double helix at the replication fork, separating the parallel strands
What is the second step in DNA replication
Step 2/7
Single-stranded binding proteins (SSBP) will bind to unpaired DNA strands, keeping them from reforming hydrogen bonds
What is the third step in DNA replication
Step 3/7
Topoisomerase will help relieve the twists and strains in DNA by breaking, swiveling, and rejoining segments
What is the fourth step in DNA replication
Step 4/7
RNA primase will place RNA primers that can act as a beginning nucleotide sequence to which DNA nucleotides can attach
What is the fifth step of DNA replication
Step 5/7
DNA pol. III will add nucleotides to the 3’ end of pre-existing chain through dehydration reactions
What is the sixth step in DNA replication
Step 6/7
DNA pol. I will replace RNA primers with DNA nucleotide bases
What is the final step in DNA replication
Step 7/7
Ligase will form a bond between old nucelotide bases and bases that have just been replaced by DNA pol. I
What are okazaki fragments
Fragments of DNA being synthesized on the lagging strand. These are made as fragments because DNA can only be synthesized in the 5’ → 3’ direction. As the lagging strand is 3’→5’, it must be built in blocks with multiple RNA primers
What is dATP
Each new nucleotide begins as a deoxyribose ATP (or appropriate base, GTP, etc.). After attaching to the DNA strand, two phosphate groups break off
What is a mismatch repair
A mismatch nucleotide base pair that must be removed and replaced by the enzyme nuclease
This repairing of DNA is not part of synthesis
When DNA is damaged, nuclease will remove a segment of DNA, or, only the damaged DNA
A segment of of DNA
In linear DNA, systems cannot complete the ____ ‘end of the daughter strand because ________________.
5’
DNA polymerase cannot add nucleotides to the new strand if there is no beginning
What is a telomere
A special sequence of DNA in eukaryotic cells that contain no genes, but rather DNA is full of repititions of short nucleotide sequences
What are the 2 functions of telomeres
- Prevent staggered ends from activating DNA damage-repair systems
- Acts as a buffer to provide protection of gene shortening
What is a histone
DNA packing form with ~100 amino acids that is positively charged and binds with phosphate groups
What is a nucleosome
DNA packing form with DNA wound twice around protein core of 8 histones
The complex of DNA and protein that makes up a eukaryotic chromosome is properly called:
Chromatin
The amount of DNA is measured in a cell and it is found that the quantity of DNA in the cells double during:
The S phase
If a human somatic cell is just about to divide, it has ____ chromatids
92
Assume you are dealing with a species in which the number of chromosomes in each somatic cell is 14. How many sister chromatids are present in the early telophase of mitosis
0
This question is dumb but the answer is because once sister chromatids have separated, they are technically now called chromosomes and not chromatids
Following cytokinesis in an animal cell, how many centrioles are present in each new daughter cell
Two
Each daughter cell inherits one centrisome which contains two centrioles
