molecular biology Flashcards
(22 cards)
name the pyramidines and purines
pyramidines: cytosine, thymine (uracil in RNA)
purines: adenine, guanine.
G&C or A&T rich DNA is more stable and why
G&C rich DNA, 3 H-bonds over 2 H-bonds btwn. A&T
Name the differences between eukaryotic and prokaryotic DNA
Prokaryotes: single circular DNA; double helix looped into a circle
Eukaryotes: several linear chromosomes
How to prokaryotes protect their DNA
Through DNA methylation or by packaging DNA in smaller units by supercoiling the DNA using DNA gyrase
How does DNA coil in eukaryotes?
-DNA gets wrapped around 8 histones to make nucleosides
-nucleosides coil upon themselves to form chromatin
What is a centromere and a telomere
centromere: region where chromatids attach
Telomere: ends of the chromosome; made of both single and double stranded DNA; consisting of short nucleotide repeats
How to telomeres stabilize the ends of chromosomes
Telomeres cap the end of chromosomes stabilizing
What is the central dogma
DNA —> RNA —> Proteins
Name the start and stop codons
Start: AUG
Stop: UAA, UGA, UAG, UGG
(You are annoying, you go away, you are gone)
** remember that the first three do not code for a specific amino acid**
UGG codes for tryptophan
What are point mutations and what protein makes the mistake that causes these?
Point mutations are single base pair changes caused by polymerase errors
Name and define the three different point mutations
1) missense: codon for an amino acid becomes a different codon that specifies for a different amino acid
2) nonsense: codon for an amino acid becomes a STOP codon which creates a shortened protein
3) silent mutations: codon for an amino acid becomes a new codon for the same amino acid
What are frameshift mutations and what are they caused by?
Frameshift mutations involve insertions or deletions of amino acids because of polymerase errors; this changes the reading frame
What do transposons consist of?
Consists of Transposase ( cut & paste enzyme)
What is the first type of Transposon? How does it work?
- Invented sequence (IS) element
How it works: Code for “cut & paste” transposase enzyme
*Contributes to genomic variation
What is the second type of Transposon? How does it work?
- Complex Transposon: has genes included within IS
How it works: transposase cuts transposon out
*Contributes to genomic variation
What is the third type of Transposon? How does it work?
- Composite Transposon: Two transposons franking central region of DNA –>
a. if the 2 transposase run in the same direction they loop over each other, causing larger deletion of DNA and then chromosomal rearrangement,
b. if they are in opposite directions, DNA gets inverted, chromosomal rearrangement within same chromosome
How it works:
Transposase pastes transposon somewhere else
- if inserted in intergenic region(region of DNA in between 2 genes) : no problem
- if inserted in coding region(middle of gene): mutations
*Contributes to genomic variation
Source of Mutation: Polymerase Errors
What are its effects on DNA and what is it repaired by?
Effects:
1. Point mutations
2. Small Repeats
3. Insertions/deletions(small, frameshift)
Repaired by:
1. mismatch repair pathway(after replication)
2. nucleotide excision repair(before replication)
Source of Mutation: Endogenous Damage(reactive oxygen species and physical damage)
What are its effects on DNA and what is it repaired by?
Effects:
1. oxidized DNA
2. cross-linked bases
3. physical damage
4. these can lead to polymerase errors
Repaired by:
1. nucleotide excision repair
2. homologous/non-homologous end joining
Source of Mutation: Exogenous damage(radiation, chemicals)
What are its effects on DNA and what is it repaired by?
Effects:
1. UV rad = pyrimidine dimers
2. X rays = double stranded breaks & translocations
3. chemicals = can lead to physical damage, intercalation & polymerase errors
Repaired by:
1. direct reversal by white light (dimers)
2. homologous/non-homologous end joining
3. nucleotide excision repair
Source of Mutation: Transposons (jumping genes)
What are its effects on DNA and what is it repaired by?
Effects:
1. insertions/deletions (large)
2. inversions
3. duplications
Repaired By:
1. generally don’t lead to repair mechanisms
What does a Mismatch Repair Pathway do? When is it detected? What is the problem and what is the solution?
- repairs bases due to DNA polymerase errors
- detected after replication is complete
Problem: which is original parent strand (correct) and daughter strand (mismatched)
Solution: methylation on parent strang for identification
When does a nucelotide excision repair occur? why? How do you do this?
- occurs prior to replication because defective bases will lead to polymerase errors
- simply remove and replace
