Structure and replication of DNA Flashcards
What is DNA?
A nucleic acid
A macromolecule
What is DNA made of?
Two polynucleotide chains
What is each polynucleotide made up of?
Many nucleotides
What does a nucleotide consist of?
5-carbon sugar (deoxyribose)
Nitrogen containing base
Phosphate group
Name the four bases
Adenine
Thymine
Cytosine
Guanine
What is a nucleoside?
Sugar + base
What is the bond between the sugar and the base?
A glycosidic bond
What is the bond between the sugar and the phosphate?
A phosphodiester bond
Why is DNA described as anti-parallel?
The two strands run parallel to each other but in opposite directions
How many hydrogen bonds are there between adenine and thymine?
Two
How many hydrogen bonds are there between cytosine and guanine?
Three
Which two bases are purine?
Adenine
Guanine
Which two bases are pyramidine?
Cytosine
Thymine
How does a purine base differ from a pyramidine base?
Purine bases have two rings
Pyramidine bases have one ring
What is the major groove?
The space between two turns of the double helix
What is the minor groove?
The space between two strands of DNA
What is meant by the 5 prime end?
The 5 carbon sugars are asymmetrical
The side the 5th carbon is found is the 5 prime end
Describe asexual reproduction in prokaryotes
Entire genome in one circular chromosome The chromosome replicates once Two chromosomes migrate to opposite ends of the cell Cell divides Daughter cells have 1 chromosome each
Describe asexual reproduction in eukaryotes
DNA replicates during S phase
Gene expression occurs in G1 and 2
Nuclear division occurs in mitosis
Cell division occurs at the end of mitosis
Why is DNA replication described as semi-conservative?
The strands separate
A new strand is made using an old strand as a template
Which is the first enzyme involved in DNA replication?
Helicase unwinds the double helix DNA
Which is the second enzyme involved in DNA replication?
Single-strand binding protein binds to and stabilises the single strand to keep DNA unwound
Which is the third enzyme involved in DNA replication?
DNA primase adds ribonuceloside triphosphate to synthesise and RNA primer
What is the fourth enzyme involved in DNA replication?
DNA polymerase proceeds in a 5’ to 3’ direction
What rate does DNA polymerase work at?
1000 bases a second
What 3 things does DNA polymerase rely on?
Template
Primer
All 4 nucleotides
What is the fifth enzyme involved in DNA replication?
Exonuclease removes nucleotides from the end of a DNA strand
Has a 5’ to 3’ and 3’ to 5’ version
What is the sixth enzyme involved in DNA replication?
Ligase joins ends of single DNA strands by making new phosphate bonds
How does RNA differ from DNA?
Single stranded
Uracil instead of thymine
What is the name given to the adding of nucleotides by DNA polymerase?
Elongation
What does exonuclease remove?
The RNA primer
What names are given to the two strands?
Leading and lagging
What causes differences in the two strands?
DNA polymerase has to work 5’ to 3’
What happens to the lagging strand?
It is fragmented
These fragments are called Okazaki fragments
How many origins of replication are there in prokaryotes and eukaryotes?
Prokaryotes have one
Eukaryotes have many
What is the seventh enzyme involved in DNA replication?
Gyrase relaxes supercoils produced when the molecule is twisted during replication
Also facilitates unwinding at the beginning
What is the eight enzyme involved in DNA replication?
Telomerase uses a short RNA template to add short DNA repeats to the short ends of linear chromosomes when the last primer is removed using RNA template
What is the name given to the point at which the double strand splits?
Replication fork
