Biochem Lecture 14-15
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Biochem Lecture 14-15
Flash cards from medical school biochemistry
What are three diseases that involve DNA repair
Xeroderma pigmantosa --> Pyrimadine dimer problems
Ataxia telangiectosia --> ATM problems
HNPCC (Lynch Syndrome)
What are the parts of Interphase?
G1, S, and G2
Name two Tumor Suppressor Genes
p53 and RB
Which phase involved the condensing of chromosomes?
Which chromosomes are Acrocentric?
13, 14, 15, 21, and 22 are the acrocentric chromosomes. These chromosomes give rise to ribosomal RNA
When does crossing over occur?
Prophase of meiosis I
What is the consequence of nondisjunction?
anueploidy – The chromosomes pair and don’t split
How many copies of mtDNA are there per mitochondrion?
between 2 and 10
What does mtDNA code for?
13 protein coding genes (for proteins involved with ATP synthesis), 2 genes for ribosomal RNA, and 22 tRNA genes
Where did your mitochondria come from?
all from mother, and do not follow Mendelian inheritance patterns
Which has greater gene density, E. coli or Humans?
E. Coli, by about 100X
List the types of DNA and their prevalence
repetitive (50%), heterochromatin (8%), regulatory (17%), Intronic (23.5%), Coding (1.5%)
What allows for the start of the origin of replication
DNaA, which melts the DNA at the origin of replication, allowing for polymerases to gain access
What do the 3' and 5' mean?
3' = hydroxyl group, 5' = phosphate group
what stabalizes unwound ssDNA?
ssDNABP (single strand DNA binding proteins)stick the the unwound strands
What unwinds DNA?
What are the types of topoisomerases and what do they accomplish?
Type I DNA Topoisomerases- cut one DNA strand to relax supercoils then seal the nick
Type 2 DNA Topoisomerases- cut Both strands, allow the supercoil to relax, then seal the nick
What are two drugs that target topoisomerases?
Etopside is an anticancer agent that targets human topoisomerase II
Quinolones target bacterial DNA gyrase, which is a type II topoisomerase
What removes RNA primers in Prokaryotes and in Eukaryotes
Prokaryotes - DNA polymerase I
Eukaryotes - RNaseH and FEN1
What are the key eukaryotic DNA polymerases?
Pol alpha - primase activity that adds a short piece of DNA to RNA primer
Pol delta - elongates strand and has 3' to 5' exonuclease activity
Pol epsilon - fills in the gap after the primer is removed
What is a way to block DNA elongation?
Nucleoside anologs with modified sugars are used for anti-cancer (cytarabine) or antiviral (zidovudine -AZT) treatment because they block DNA elongation.
Four functions of telomeres
1) Ensure that Genes are fully replicated
2) Protect the end of chromosomes by having repetitive AGGGTT
3) Shorten with Age (when gene replication is compromised, cell stops dividing
4) Do not shorten in cancer cells or stem cells because these cells express telomerase
What is telomerase
an enzyme comprised of protein and a short piece of RNA (thus a ribonucleotide)
has reverse transcriptase activity
maintains telomere length
expression of telomerase in primary cell lines results in their imortalization
What are the 5 classes of histones?
H2A, H2B, H3 and H4 form the nucleosome core, while H1 binds DNA between nucleosome beads (the linker histone)
How do histones impact gene expression?
the histones can be modified, (acetylated, methylated, and phosphorylated) especially on N-terminal tails which alters gene expression
How is DNA packed into a chromosomal structure?
It is first wound around histones, forming nucleosome beads, then packed more tightly into a 30nm fiber, and eventually into the final chromosomal structure
which direction does DNA polymerase read the parental strand and synthesize new DNA?
Reads parental strand from 3' to 5'
synthesized new DNA from 5' to 3'
What does DNA polymerase III accomplish?
catalyzes chain elongation (5' to 3' polymerase activity)
proofreading (3' to 5' exonuclease activity)
What does DNA polymerase I do?
looks for nick between 3' end of new DNA and 5' end of RNA primer
Removes RNA primer (5' to 3' exonuclease)
fills in gaps accurately (5' to 3' polymerase, 3' to 5' exonuclease)