DNA Replication & The Cell Cycle Flashcards
What does DNA stand for?
Deoxyribonucleic Acid
What is the function of DNA?
The sequence of nucleotides in DNA determines the amino acid sequence that makes up proteins.
What is some history of DNA?
Rosalind Franklin determined the structure of DNA with the help of x-ray diffraction. Later, Watson and Crick built a 3D model of DNA using Franklin’s x-ray diffraction.
What is the structure of DNA?
It is a double helix with two nucleotide chains in the shape of a twisted ladder. (the sides of the ladder are phosphate and sugar and the rungs are nitrogen bases)
Is DNA parallel or antiparallel?
Antiparallel, sides in opposite directions.
What are hydrogen bonds role in DNA?
Hydrogen bonds hold nucleotide chains together (loosely)
What is complementary base pairing?
The percentage of adenine will approximately equal the percentage of thymine (same for cytosine and guanine)
What are pyrimidines and purines?
pyrimidines are single-ringed while purines are double-ringed (purines bond with pyrimidines)
What does RNA stand for?
Ribonucleic Acid
Describe RNA.
Single stranded, uracil instead of thymine, ribose instead of deoxyribose, 3 types (rRNA, tRNA, and mRNA)
What is the binding of enzymes called in DNA replication?
Replisome (combo of DNA and enzymes)
How does bonding work in DNA replication?
Enzymes bond to DNA at replication origins (many on each DNA) usually a lot of A-T bonds because they are easier to break than C-G bonds.
Why doesn’t the sugar-phosphate backbone break like the nitrogen bases?
They are held together by strong covalent bonds.
What is the first step in DNA replication?
Helicase unwinds the helix (unzips)
What is the second step in DNA replication? (After helicase unwinds the helix)
Strand stabilizing proteins keep the DNA unwound.
What is the third step in DNA replication? (After strand stabilizing proteins keep the DNA unwound)
DNA polymerase only moves in the 3’ to 5’ direction as it synthesizes the new strand continuously.
What is the fourth step in DNA replication? (After DNA polymerase only moves in the 3’ to 5’ direction as it synthesizes the new strand continuously)
Primase makes RNA primer so DNA polymerase can attach and discontinuously synthesize a copy in short pieces call Okazaki fragments.
What is the fifth step in DNA replication? (After primase makes RNA primer so DNA polymerase can attach and discontinuously synthesize a copy in short pieces call Okazaki fragments)
RNA primer is replaced by DNA polymerase. Ligase joins the Okazaki fragments forming a long strand of DNA.
What strand does primer add RNA primer to?
Leading strand
How does DNA polymerase add new nucleotides?
in the 5’ to 3’ direction on leading strand and in discontinuous fashion to lagging strand.
What does DNA polymerase replace primers with?
DNA bases
What does DNA ligase do?
Seals holes of Okazaki fragments
Describe DNA replication.
semi-conservative and happens in multiple “bubbles”
What is DNA repair?
Errors, mutation can cause birth defects, cancer, or diseases
what is DNA repair’s defense?
DNA polymerase proof reads its own work and removes and replaces errors
What is Excision Repair?
Ex: mismatch A-G, excision enzyme removes error, DNA polymerase fills in correct bases (ATGC), Another enzyme adds in phosphate and sugar
What are chromosomes?
made of nucleosomes - DNA wraps around histones (proteins), when DNA is tightly wrapped, it turns that section of DNA off (enzyme cant get to DNA until helicase unwinds it)
What are the stages of the cell cycle?
G1, G0, S, G2, M, (cytokinesis)
What does G1 do in the cell cycle?
grow, metabolism, make proteins, RNA and biomolecules.
What does G0 do in the cell cycle?
Non-dividing most adult cells (ex. Liver cells) Still doing job but not going anywhere.
What is the restriction point in the cell cycle?
signal needed continue on “POINT OF NO RETURN”
What does synthesis do in the cell cycle?
Chromosome (DNA) Replication
What does G2 do in the cell cycle?
make protein, RNA, organelles, get ready to divide
What does Mitosis do in the cell cycle?
Division of Nucleus (PMAT)
What are the stages of cell division?
Interphase, Prophase, Metaphase, Anaphase, Telophase, (Cytokinesis)
What is interphase?
G1, S, and G2 (Chromosomes not visible, less condensed, Chromatin (DNA)) Everything BUT mitosis
What is prophase?
- Chromosomes condense and become visible
- Nuclear membrane breaks down - stored in vesicles
- Centrioles moved to opposite ends of cell
(Nucleus Gone)
What is Metaphase?
Replicated chromosomes line up down the MIDDLE, Metaphase Plate: Middle or equator
What is Anaphase?
- Enzyme breaks down centromere
- Spindle fibers pull sister chromatids apart
What is Telophase?
- Two nuclear membranes form
- Spindle fibers disappear
- Chromosomes uncoil
- Cells begin to split
What is cytokinesis?
Division of cytoplasm (cells split) technically NOT mitosis
What is external regulation?
Proteins in the cell respond to signals from outside. Growth Factors: Increase growth and division (embryo and injury), Molecules from neighboring cells inhibit growth or influence growth
What is Internal Regulation?
Proteins in the cell (aka tumor suppressors) respond to signals from inside the cell.
What are checkpoints?
Checkpoints control the cell cycle➜Stop and Go Signals
What are the 3 main checkpoints?
G1, G2, and M
What does the G1 checkpoint do?
Determines if the cell should divide, delay division, or enter G0
What does the G2 checkpoint do?
Trigger the start of M, ensures DNA replication was successful
What does the M checkpoint do?
End of metaphase, triggers exit from mitosis and cytokinesis, daughter cells can begin G1
What are Cyclins?
Proteins that regulate movement through cell cycle, bind to kinases, cyclins are destroyed and resynthesized during each turn of the cell cycle
What are Kinases?
Enzymes that only function when the correct cyclin (substrate) is bound to it, once active, the kinase activates or deactivates another enzyme (needed for progression of the cell cycle) by phosphorylation, amounts of kinase are constant, activity is regulated by presence or absence of cyclins, give “go ahead” signals at checkpoints
What does phosphorylation mean?
transferring a phosphate
G1 checkpoint Example
G1 cyclins accumulate when the cell gets its signals to prepare for the cell division (end of G1) and this triggers DNA replication
G2 checkpoint example
during G2, cells accumulate mitotic cyclin (push cells out of G2 and into mitosis)
What does mitotic cyclin + kinase do?
Activates nuclear membrane breakdown and chromosomes condense
More mitotic cyclin + different kinase=
spindle fibers form, centromere break, breaks down mitotic cyclin (decreased cyclins inactivates kinase)
Describe Checkpoint Control
Monitor condition of DNA, chromosomes, and the mitotic spindle, proteins detect mistakes and damage —> cell cycle stops (cell arrest) until repaired.
Checkpoint control order
- Monitors DNA mistakes (mismatched bases)
- DNA mistakes activate cell cycle inhibitors - stop things
- Preventing G1 cyclin-kinase so cell can’t go to S phase
- Once damage is repaired…p53 becomes inactive…DNA replication can proceed.
What does unregulated cell cycle mean?
cancer cells don’t respond to signals so they grow uncontrollably - not having p53=cancer
What is cancer? (in cell cycle terms)
When cells aren’t following the cycle (not doing routine)
What are proto-oncongenes?
genes that promote cell division (cyclins/kinases), code for proteins that help regulate cell growth
What are tumor-suppressor genes?
inhibit cell division (p53), code for proteins that prevent uncontrolled cell division
What bad thing can proto-oncongenes and tumor-suppressor genes lead to?
mutations
What are oncongenes?
cancer genes cause cells to leave G0 and divide even when there is no signal (make too much or too quickly) (Mutations in proto-oncongenes)
