DNA and DNA replication Flashcards
The amount of adenine…
equal amount of thymine
The amount of guanine…
equals amount of cytosine
Purines
*Double ring structure (A,G)
Pyrimidines
*Single ring structure (C,U,T)
How are nucleotides held together?
Hydrogen bonds
Key features of DNA
- Double-stranded helix, antiparallel strands
- Sugar-phosphate backbone
- Nucleotides pairing in the center
Key function of DNA
Primary source of heritable information, genetic info stored and passed from one generation to the next through DNA.
EXCEPTION RNA primary source of heritable info in some viruses
Eukaryotic Cells DNA
- DNA found in nucleus
- Linear chromosomes
Prokaryotic Cells DNA
- DNA in nucleoid region
- Chromosomes are circular
Plasmids
Small, circular DNA molecules that are separate from the chromosomes
Plasmids importance
Contain genes that may be useful to the prokaryote when it is in a particular environment
Plasmids and manipulation in laboratories
*Plasmids can be removed from bacteria, then a gene of interest can be inserted into the plasmid to form recombinant plasmid DNA
*When recombinant plasmid is inserted back into the bacteria the gene will be expressed
RNA
-Ribonucleic acid
-Single stranded
-A=U C=G
DNA
-Deoxyribonucleic acid
-Double stranded
-A=T C=G
Models of DNA replication
- Conservative
- Semi-conservative
- Dispersive
Conservative model
The parental strands direct synthesis of: an entirely new double stranded molecule
Semi-conservative model
*The two parental strands: Make a copy if itself
*After one round of replication, the two daughter molecules each have one parental and one new strand
Dispersive model
*The material in the two parental strands is dispersed randomly between the two daughter molecules
*After one round of replication, the daughter molecules contain a random mix of parental and new DNA
1st step in DNA replication
- DNA replication begins at sites called origins of replication, various proteins attach to the origin of replication and open the DNA to form a replication fork
2nd step in DNA replication
- Helicase will unwind the DNA strands at the replication fork
-To keep DNA from re-bonding to itself, single strand binding proteins bind to the DNA to keep it open
-Topoisomerase will prevent strain ahead of the replication fork by relaxing supercoiling
4th step in DNA replication
Antiparallel elongation
*DNA polymerase III: Attaches to each primer on the parental strand and moves in the 3’ to 5’ direction
-Adds nucleotides in the 5’ to 3’ direction
*DNAP III that follows helicase is known as the leading strand and it only requires one primer
-DNAP III on other parental strand, know as the lagging strand and requires many primers
3rd step in DNA replication
- The enzyme primase initiates replication by adding short segments of RNA, called primers to the parental DNA strand
-The enzymes that synthesize DNA can only attach new DNA nucleotides to an existing strand of nucleotides
-Primers serve as the foundation for DNA synthesis
5th step in DNA replication
*The leading strand is synthesized in one continuous segment, but since the lagging strand moves away from the replication fork, it is synthesized in chunks
Okazaki fragments: Segments of the lagging strand
6th step in DNA replication
*After DNAP III forms an Okazaki fragment, DNAP I replaces RNA nucleotides with DNA nucleotides
DNA ligase: Joins the okazaki fragments forming a continuous DNA strand
