DNA Structure and Replication Flashcards
What are the parts of a nucleotide?
A sugar (either ribose or deoxyribose), a phosphate, and a nitrogenous base.
What are the pyrimidine bases?
Thymine and Cytosine
What are the purine bases?
Adenine and Guanine
What kind of base is represented by a pentagon?
A purine
What kind of base is represented by a hexagon?
A pyrimidine
In the arrangement of nucleotides, what does the sugar bond to?
The last phosphate at carbon 3.
In the arrangement of nucleotides, what does the phosphate bond to?
The next sugar at carbon 5.
What is the sugar end of the strand called?
3’ end
What is the phosphate end of the strand called?
5’ end
How many bonds does adenine form with thymine?
2
How many bonds does cytosine form with guanine?
3
Which kind of bonds would a more stable section of DNA have more of?
More stable sections would have more CG bonds.
What happens if the amount of adenine does not equal the amount of thymine?
DNA is not double stranded
What happens if the amount of cytosine does not equal the amount of guanine?
DNA is not double-stranded.
How are the strands in DNA arranged?
In a double helix.
How many base pairs are in a human cell
3 billion
How many genes are the 3 billion base pairs in a human cell arranged into?
25 000 genes
What percentage of genes do not code for any protein?
Up to 50 % of genes do not code for ANY PROTEIN!
How long is the DNA from one cell?
2 m in length.
What is a disadvantage [ssDNA] has?
It is easily broken.
What is an advantage [dsDNA] has?
It is very stable.
Name five differences between RNA and DNA.
- The sugar used is ribose (has one more oxygen than deoxyribose).
- Adenine bonds to uracil instead of thymine.
- Single-stranded molecule.
- Much shorter than DNA.
- Unlike DNA, RNA can survive in the cytoplasm if properly prepared. (student losing notes vs losing textbook)
What is the order of steps in DNA replication?
- Starting
- Building
- Other Strand
- Finishing
What does DNA helicase do?
Breaks H bonds between strands at an “origin of replication”
What does DNA gyrase do?
Releases tension that comes from unwinding.
What is the replication fork?
The area where the two strands are separated.
What are single stranded binding proteins for?
To keep strands from reannealing.
What does Primase do?
It creates a 10-60 base pair strand of RNA (RNA primer) et the exposed end of 3’ of replication fork.
What does DNA polymerase III do?
It moves along the old DNA in the 3’ to 5’ direction and adds complementary bases that are phoshorylated (removing 2 Pi)
What is the leading strand?
The strand continiously copied from the 3’ to 5’ end.
What is the lagging strand?
The strand made from attaching Okazaki fragments together.
Why is the lagging strand built in fragments?
Because DNA polymerase III casn only move in the 3’ to 5’ direction.
What does DNA polymerase 1 do?
It removes RNA primers and replaces them with the appropriate DNA bases.
What does DNA ligase do?
It attaches Okazaki fragments by bonding sugar and phosphates.
