DNA Flashcards
What are the dips called in DNA?
Major groove
Minor groove
What direction is the spiral?
Right handed
What is the outside of DNA made from?
Phosphate backbone
Where are genes located?
Located on chromosomes
How many chromosomes does a human have?
How many are autosomal?
23 pairs - 22 autosome
How does the size of the Y chromosome compare to X?
Y is much smaller
What section of the sex chromosome determines sex determination?
Pseudoautosomal region
How is DNA stored in a cell? (2)
Tightly wound around histones proteins
Packaged in chromosomes in the nucleus
What is the heavily condensed section of chromosome?
What does this mean?
Heterochromatin
DNA is tightly bound around histones
What is the less condensed section of chromosome?
Euchromatin
Why is the DNA in an open configuration?
Allows the DNA to be transcribed
What is the name of the secondary structure of multiple histone proteins wound together?
Solenoid
Are genes on Heterochromatin expressed?
Why?
No
So compact that transcription factors cannot access
What are DNA and RNA both?
Nucleic acids
Difference between the sugar of DNA and RNA?
R - OH on the bottom right
D - H on the bottom right
Structure of a nucleotide
Pentode sugar
Nitrogenous base
Phosphate group
Name the two types of bases
Purine
Pyramidal
Two types of purine base
A
G
Three types of pyrimidine bases
C
U
T
What is the difference between a nucleoside and nucleotide?
Nucleoside is a sugar and base
Nucleotide has a phosphate as well
What type of bond is a phosphodiester bond?
Covalent
What describe the polarity of the chain and what it starts and ends with
5’ to 3’
P to OH
How many H bonds are between:
CG
AT, AU
3
2
What are the two strands called in DNA?
Describe the function
What direction of prime
Coding - not transcribed into mRNA, 3’ - 5’
Complimentary - opposite
Describe in two words how the two strands of DNA compare
Reverse complimentary
At what stage of the cell cycle is DNA replicated?
S phase
What catalyses DNA replication and how?
DNA polymerase
Catalyses bonds between bases
What are the three steps in prokaryotic DNA replication?
Initiation
Elongation
Termination
What direction does the DNA chain grow?
5’ to 3’
Describe the chromosomes in prokaryotes
Single
Circular
Where does DNA replication begin in a prokaryote?
Origin
Describe initiation
What does it require? - prokaryotic
Recognition of origin
DNA polymerase, specific proteins, primase
Why is primase required in initiation?
DNA can only add to the 3’ end
Describe elongation - prokaryotic
Replication forks move
Helicase unwinds the double helix
DNA polymerase extends the 3’ end only - creating three types of strands
DNA ligase joins fragments
What does DNA polymerase create in elongation? (3) - prokaryotic
Leading strand - continuous
Lagging strand - discontinuous
Okazaki fragments
What is the product of elongation? - prokaryotic
Complete copy of the chromosome
What is a replication fork?
The point at which the two strands of DNA are separated, to allow replication of each strand
What do eukaryotes have when DNA helicase breaks bonds between bases?
Replication bubbles
Describe initiation - eukaryotic
Primase makes an RNA primer
Allowing DNA polymerase binds at 3’ end, within the origin of the leading strand
What are the two strands of the unwound DNA helix called?
Leading - coding strand, used to produce the amino acid sequence
Lagging - opposite complimentary strand
Describe elongation - eukaryotic
The DNA polymerase moves along the leading strand from 3’ to 5’
A second DNA polymerase binds to 3’ end of the lagging strand - copying and creating Okazaki fragments
DNA binds the fragments
DNA wound into a helix using helicase
Why can only a short section of DNA be copied on the lagging strand?
The 3’ end of the lagging strand is close to replication fork
What happens to the leading strand after the helix is unwound?
The leading strand is elongated
What are Okazaki fragments?
Why do they exist?
The lagging strand is copied in short fragments
The DNA is still be unwound as the lagging strand is copied - as there is only a short section that can be copied
What is the product of eukaryotic DNA replication?
Two new identical copies of the original DNA
Describe termination - eukaryotic
Two replication bubbles meet, causing the molecule to separate into fragments
DNA ligase joins together the fragments
What is a chromosome made of?
1 DNA molecule
What are the two states a chromosome can exist in?
Describe them
Replicated - sister chromatid joined by a centromere
Unreplicated
