lecture 23 Flashcards
What is the structure of DNA?
Two DNA strands with sugar-phosphate backbone and base (ATCG) in the middle
How are two stands of DNA held together?
Two strands held by hydrogen bonds (2 vs 3) forming double helix
Is DNA negative or positive, why?
Negative charge on phosphate (hence nucleic acid)
How many base pairs i the human genome?
3x10^9 bp
True/False: Gene has defined sequence and size
true
What are the Key concepts that led to the discovery of DNA’s 3D structure
Chargaff’s rule
Sugar phosphate backbone positioned outside and nucleotide facing inside
Signature diffraction pattern
suggesting double helix structure.
What is chargaffs rule?
In any species the number of A and T bases are equal, and the number of G and C bases are equal.
What did the Signature diffraction pattern suggest?
double helix structure
How is the turn in DNA structured?
every 10 bp
What are the purines?
A and G
What are the pyrimidines?
T and C
How many bonds do A and T form?
2 hydrogen bonds
How many bonds do C and G form?
3 hydrogen bonds
What did Dr. Marie Maynard Daly do?
first african american to receive a Ph.D from Columbia University and the first African American women to receive a chemistry Ph.D in the United States
What did Dr. Marie Maynard Daly research?
fractionation & preservation of nuclear components and discovery of important lysine amino acids in histone proteins
DNA is organized into _____.
chromosomes
What is Chromatin made up of?
DNA and histone (protein)
DNA is a polymer of ____.
nucelotides
Chromosomes are condensed ___.
chromatin
What are telomeres?
a region of repetitive DNA sequences at the end of a chromosome.
What does DNA replication ensure?
the continuity of cell characteristics with each division
DNA replication is ____. (energy)
semiconservative
What is the origin of DNA replicatipn?
at nucleotide-rich (AATATA) DNA sequence
replication occurs in both directions
What enzyme participates in DNA replication?
DNA polymerase (and many others)
What does DNA polymerase do in DNA replication?
adds nucleotide to 3’ end and extends the chain from 5’ to 3’
What is the function of helicase?
unwinds parental double helix at replication forks
What does single-strand binding protein do?
binds to and stabilizes single-stranded DNA until it is used as a template
What does topoisomerase do?
relieves overwinding strain ahead of replication forks by breaking, swiveling, and rejoining DNA strands
What does primase do?
synthesizes an RNA primer at 5’ end of leading strand and at 5’ end of each Okazaki fragment of lagging strand
What does DNA pol III do?
using parental DNA as a template, synthesizes new DNA strand by adding nucleotides to an RNA primer or a pre-existing DNA strand
What does DNA pol I do?
removes RNA nucleotides of primer from 5’ end and replaces them with DNA nucleotides
What does DNA ligase do?
joins Okazaki fragments of lagging strand; on leading strand, joins 2’ end of DNA that replaces primer to rest of leading strand DNA
How is the leading strand synthesized?
-DNA pol I replaces RNA sequence (also called as primer) with DNA nucleotides. Adds nucleotides to 3’ end (like DNA polymerase III)
-DNA ligase forms bonds between two DNA fragments.
How is the lagging strand formed?
-DNA pol I replaces RNA primer with DNA nucleotides (for each Okazaki fragment).
-DNA ligase forms bonds between DNA fragments.
-Joins Okazaki fragments to form a lagging strand
What is a pyrimidine dimer?
a kink caused by UV light in DNA, thymine dimer forms
