Lecture 2/3 Flashcards
approximately how many genes are we estimated to have?
40,000 (many noncoding ones)
how are chromosomes numbered?
by size (1 is biggest)
what are the 3 major differences between RNA and DNA?
- ribose vs. deoxyribose sugar
- Uracil instead of Thymine
- most RNAs are single stranded
What is on carbon 2 in RNA? DNA?
RNA: hydroxyl
DNA: hydrogen
RNA is single stranded, how does it get interesting secondary/tertiary structures?
by binding to itself – it needs to fold into certain structures to function / so certain amino acids can attach
How does a molecule carry information?
base sequence
how is information from a gene transmitted to future generations?
DNA replication
what 2 mechanisms allow genetic information to change?
- recombination
- mutations
how does DNA-encoded information govern the expression of phenotype?
gene functions – DNA instructions are transcribed into RNA and then translated into proteins, which influence an organism’s phenotypes
how do somatic cells spend their time?
either in G0 (hanging out) or actively going through mitosis (cell cycle)
are germ cells always haploid?
no, they’re initially diploid during embryogenesis before they’re differentiated
what cell cycle do gametes go through?
meiosis
what is the genome
the sum of genetic information in a haploid set of chromosomes
what is a haploid genome
the genetic content of a gamete
how is the DNA content of a haploid cell represented?
n
how is the DNA content of a diploid / somatic cell represented?
2n
how is the DNA content of a tetraploid cell represented?
4n
how many chromosomes in a human egg?
23
how many chromosomes in a human somatic cell?
46
does the number of chromosomes in an organism relate to the complexity of the organism?
no
how long is a full cell cycle for a human cell in vitro?
approx 24 hours
What happens at G1 in the cell cycle?
it is the checkpoint for mitosis, proteins for DNA replication are made; takes approx 10 hrs
What happens at S in the cell cycle?
DNA replication, ~9hrs in vitro
What happens in G2?
checkpoint for DNA replication, proteins for mitosis are made; ~4hrs
what happens in mitosis, and what are the 4 stages?
cell division: ~1hr
Prophase
Metaphase
Anaphase
Telophase
what cells are postmitotic at birth?
nerve cells
if there are mistakes in DNA replication, at what point in the cell cycle would they be fixed?
G2
In mitosis, how many chromosomes do daughter cells have in comparison to the parent cells?
the same number
once divided, is every part of the daughter cells of a fertilized egg exactly the same?
only if they’re twins, otherwise at least the cytoplasmic components are likely to be different
How is DNA compacted?
DNA is wrapped around histone protein cores to make a nucleosome
what repeating unit is formed by nucleosomes?
chromatin
In a non-dividing somatic cell, what is the DNA content of the cell?
2n
How is DNA organized during interphase?
Before cell division, DNA exists in a loosely organized form called chromatin, which is not visible as chromosomes.
How is DNA organized during prophase?
As the cell enters prophase, the chromatin coils and condenses, becoming tightly packed into visible chromosomes.
Is DNA condensed during mitosis?
yes, and it is visible as chromosomes
what is it called when DNA is wrapped around histones to fit in the nucleus?
compaction
are chromosomes randomly placed or organized
organized, they each have their own little territory
what are the three possible models of DNA replication?
semi-conservative (correct)
conservative
dispersive
what is semi-conservative DNA replication
2 parental strands separate and each form template strands; new strand forms by insertion of complementary base pairs, single double helix becomes 2 identical daughter double helices
what is the concept of conservative DNA replication
parental double helix remains intact, both strands of daughter helices are newly synthesized
what is the concept of dispersive DNA replication
both strands of both daughter helices contain original and newly synthesized DNA
In the experiment testing what the correct model of DNA replication is, how did they grow E.coli?
First in media containing 15N (heavy isotope) and then 14N (normal isotope)
Once the 15N bacteria grow for one generation in 14N and are centrifuged, where are the DNA bands?
there was one band between where one would expect 15N and where you’d expect 14N
Once the 15N bacteria grow for two generations in 14N and are centrifuged, where are the DNA bands?
you get the intermediate band and also the 14N band because of semi-conservative replication
what kind of bonds does DNA polymerase catalyze?
phosphodiester
what are the two stages involved in DNA replication?
initiation and elongation
what happens in DNA initiation?
proteins open up the double helix and prepare it for complementary base pairing
what happens in DNA elongation?
proteins connect the correct sequence of nucleotides on newly formed DNA strands
What are the proteins that bind to the origin site, unwind the helix, and keep the replication bubble open?
initiator protein, helicase and single-stranded binding proteins
how many chromosomes do bacteria have?
1
what does primase do and where does it work?
primase synthesizes RNA primer, which can only be added onto the 3’ end
in which direction does DNA pol iii elongate?
5’ to 3’
what is the difference between the leading and lagging strands?
leading strand has continuous synthesis, whereas the lagging strand has discontinuous synthesis
what is an okazaki fragment?
short DNA fragments on the lagging strand (because nothing is added on the 5’ end during replication)
what 2 processes must occur after primer elongation?
primer must be replaced with DNA sequence and okazaki fragments must be covalently joined by DNA ligase
what is used to degrade RNA primer and in which direction does it work?
DNA pol i degrades the primer using 5’ to 3’ exonuclease activity and fills in the missing nucleotides
what is used to covalently join okazaki fragments?
DNA ligase
where does DNA pol i work?
at the free 5’ end
what is used to proofread, and what direction does it go?
DNA pol iii, and it has exonuclease activity in the 3’ to 5’ direction
what is chewback in DNA replication?
the 3’ to 5’ proofreading activity – for 1 error it might remove 1000bps and then fill it in again
what forms when ligase links 2 DNA fragments together
ligase catalyzes the formation of phosphodiester bonds with the energy from bond formation
when helicase unwinds DNA, what happens ahead of the replication fork?
it creates supercoiled DNA
