DNA Replication and Cell Division Flashcards
1
Q
Hereditary Material and Expression
A
- Genetic Information stored in genes
- expression (turning in a gene) causes an effect
- regulation controls when a gene is expressed
2
Q
Frederick Griffith’s Experiment 1928
A
- Studied two strains of Streptococcus pneumoniae injected in mice
- virulent (causes pneumonia) and non-virulent
- results
- non-virulent cells became virulent when mixed with dead virulent cells
- some type of molecule in dead cells carried the genetic info to express virulence, which he did not identify
3
Q
Avery, Macleod and McCarthy’s Experiment 1944
A
- Built upon Griffith
- extracted DNA and RNA from virulent cells
- added enzymes to degrade the extracts
- only the extracts treated with an enzyme to kill DNA were unable to transform non-virulent bacteria
4
Q
Nucleotides
A
- Made up of a phosphate group attached to the 5’ binding site and a base attached to the deoxyribose sugar at the 1’ binding site
- nucleosides do not have a phosphate group attached
5
Q
Nucleotide bases
A
- Purines: adenine and guanine
- Pyrimidines: thymine and cytosine
6
Q
Phosphodiester bonds
A
- each nucleotide sugar is linked to the phosphate group of the neighboring nucleotide
- C-O-P-O-C linkage is a phosphodiester bond
- stable, can withstand changes in pH and temp
7
Q
DNA Molecule
A
- Polar, each end is different
- Anti-parallel, on side is 5’-3’, other is 3’-5’
- top of chain has a free 5’ phosphate, bottom has a free 3’ hydroxyl
- read 5’-3’, if not specified top/left is the 5’
- phosphate backbone on the outside, bases on the inside
8
Q
Base Pairing
A
- Adenine and thymine bond, held together by two hydrogen bonds
- guanine and cytosine bond, held together by three hydrogen bonds as G has an extra NH2 group
9
Q
Double Helix Discovery 1953
A
- Watson and Crick with diffraction by Rosalind Franklin, wilikins
- earlier molecules indicated a long molecule
10
Q
Chargoff’s Base Pairing RUle
A
%A=%T
%G=%C
11
Q
Replication in Prokaryotes
A
- Circular double stranded bacterial DNA is attached by proteins to the inner membrane
- begins at a specific location and moves bidirectionally around the circle
- new DNA is attached to the inner membrane, near the original
- cell elongates, attachment sites are separated
- constriction forms at the midpoint of the dividing cell
- synthesis of new cell membrane and wall separates two daughter cells
12
Q
Replication in Eukaryotes
A
- G0 phase: cells not actively dividing
- G1: prep for synthesis, two strands separate into two strands at the replication fork
- S phase: synthesis
- G2 phase: prep for mitosis and cytokinesis
- M phase: mitosis
13
Q
Hypothetical Models for DNA Replication
A
- Conservative: two new daughter strands, parental remains intact
- Semiconservative: one old and new strand each
- Dispersive: duplex split between parental and daughter
14
Q
Meselson and Stahl
A
- Synthesized DNA in mediums with different isotopes of N
- isotopes were incorporated into strands
- cells stoped replicating as eventually all had some of the isotope
- provided support for semi-conservative
15
Q
Discovery of Semi-Conservative Replication in Eukaryotes
A
- Fluorescently labelled DNA replicated
- After two replications, the DNA was photographed, one strand fluoresced the other did not
- 3’-OH group of the growing strand attacks the high energy phosphate bond of the incoming nucleotide to initiate synthesis
16
Q
Enzymes used in DNA Replication
A
- DNA polymerase: extends RNA primers, acts at the site of the growing chain on the 3’ end to lengthen one sub unit at a tome
- Helicase: unwinds the parental DNA strands at the fork
- topoisomerase II: relieves stress of unwinding, braces molecule
17
Q
Continuous/Discontinuous Replication
A
- leading strand has its 5’ end pointing at the fork, synthesized as one long continuous polymer
- Lagging strand has its 3’ end pointing at the fork, synthesized in short discontinuous sections
- These pieces are called Okazaki Fragments
18
Q
Resolving Okazaki Fragments
A
- RNA primase lays down an RNA primer
- DNA polymerase extends the RNA primer
- a different DNA polymerase removes the primer and replaces it with DNA
- DNA ligase forms a bond joining the two DNA fragments
- DNA strands have a section of RNA on the 5’ end, DNA polymerase replaces this with a nucleotide
19
Q
DNA proofreading
A
- DNA polymerase corrects rare errors
- initiates a cleavage function and replaces the nucleotide
20
Q
Replication Origins
A
- Replication occurs 50 nucleotides/second
- begins in many places to conserve time
- opening at a origin forms a bubble with a fork on each side
- bubble grows until it meets another one
21
Q
Linear DNA after Each Round of Replication
A
- each strand starts with a primer
- on the leading strand: only the primer is required to start synthesis, continues to the end,
- lagging strand: multiple primers requires, final one added about 100 nucleotides from the 3’, when removed the daughter strand is shorten by about 100 nucleotides
- each replication yields a shorter template, which can’t continue
22
Q
Telomerase
A
- end of a chromosome capped by a repeating telomere
- 5’TTAGGG-3’ repeated 1500-3000 times
- shortened every round, and replaces missing nucleotides
- scientists believe this is why tissues become less youthful with age
23
Q
Cell Theory
A
- All living things made up of cells
- basic unit of structure
- come from pre-existing cells
24
Q
Prokaryote v. Eukaryote Cells
A
- Prokaryotes: smaller, simpler, no membrane bound organelles, circular DNA
- Eukaryote: larger, complex, membrane bound organelles, mostly linear DNA
25
Types of Cell Division
- Prokaryotes: binary fission
- Eukaryotes: mitosis
- Eukaryotic gametes : mitosis
26
Chromosmes
- 22 homologous pairs and a sex chromosomes
- In the S phase, homologous pairs are duplicated and joined at the centromere forming sister chromatids
27
Two Phases of Cell Division in Eukaryotes
- M phase: mitosis
- Interphase: DNA replication G1, S, G2, G0 phase
28
Eukaryotic DNA organization - karyotype
- Organized with histones and proteins into chromatin, which are looped and packaged into chromosomes
- number and shapes of chromosomes is a karyotype
- most cells have 46 chromosomes, same set of genes, one from mother and father
29
Prophase - Mitosis
- Chromosomes condense, centromeres radiate microtubules and migrate to opposite poles
- outside the nucleus, the miotic spindle is assembled
- centrosomes (microtubule centers) are duplicated and migrate to opposite poles
- plant cells have no centrosome
30
Prometaphase - Mitosis
- nuclear membrane breaks down
- microtubules grow, shrink where the nucleus was
- microtubules attach to chromosomes centromeres
31
Kinetochores
- two protein complexes associated with the centromeres, form the site of attachment for a single microtubule
32
Metaphase
- chromosomes align in the center of the cell
33
Anaphase
- sister chromatids separate and travel to opposite poles
- centromeres divide
34
Telophase
- nuclear envelope re-forms and chromosomes decondense
- chromosomes are less visible
35
Cytokinesis in Animal Cells
- actin filaments (contractile ring) forms on the inner face of the cell membrane, contracts pinching cytoplasm forming a new wall
36
Cytokinesis in Plant Cells
- phragmoplast (overlapping microtubules) formed in telophase
- vesicles fuse with phragmoplast forming a plate
- plate eventually fuses with the original cell wall
