KA2 - Structure And Replication Of DNA Flashcards
A molecule of DNA consists of two strands each composed of repeating units called what?
Nucleotides
Name the three parts of a nucleotide
Deoxyribose sugar
Phosphate group
An organic base
Name the four DNA bases
Adenine & Thymine
Cytosine & Guanine
What position does the C3 and C5 determine?
The 3’ and 5’ end of the DNA strand
What carbon is the phosphate group attached to on the deoxyribose sugar?
Carbon 5
What carbon is the organic base attached to on the deoxyribose sugar?
Carbon 1
What is formed when nucleotides join together?
Nucleotides join together to form the DNA molecules sugar phosphate backbone
Where is a strong chemical bond formed?
A strong chemical bond is forms between the phosphate group of one nucleotide and carbon 3 of the deoxyribose sugar on another nucleotide
DNA is a double helix. What is meant by this?
There are two strands of nucleotides joined together
What type of bond joins the two strands of nucleotides to their complimentary bases?
Weak hydrogen bonds
What is determined by the sequence of bases?
An organism genotype is determined by the sequence of bases
What is at the 3’ end of each complimentary stand of DNA?
The deoxyribose sugar
What is at the 5’ end of each complimentary strand of DNA?
The phosphate grouo
How is the chain able to grow and what does this lead to?
The chain is only able to grow by adding nucleotides to its 3’ end
This leads to the two DNA strands with their sugar phosphate backbones running in opposite directions. This is described as anti parallel
What must happen in order for the complimentary base pairs to align?
The two strands in a DNA molecule form a twisted coil called a double helix
Describe the structure of the double helix
The sugar phosphate backbones are ok the outside and the complimentary base pairs are on the inside
When is DNA replication preformed?
At the beginning of cell division
Where does DNA replication take place?
In the nucleus
What is DNA replication?
DNA replication is the process by which a cell makes an identically copy of its DNA
What does DNA replication ensure?
DNA replication ensures that an exact copy of a cells genetic information is passed on to each new daughter cell making it genetically identically to the original cell
What does DNA replication maintain in the new daughter cell?
DNA replication maintains the chromosome compliment in the new daughter cell.
For DNA replication to occur, what must the nucleus contain?
DNA to act as a template
Primers
A supple of the four types of nucleotide
Enzymes (DNA polymerase & ligase)
Supply of ATP for energy
What 3 steps are preformed at the beginning of DNA replication?
- The shape of DNA is a double helix
- Before DNA can be replicated, it must first be unwound
- The weak hydrogen bonds between the bases are then broken to form two template strands
What is DNA replicated by?
DNA polymerase
What must be present for DNA polymerase to function?
DNA polymerase can only add nucleotides to a pre existing chain of nucleotides. Therefore for DNA polymerase to function, a primer must be present.
What is a primer?
A primer is a short strand of nucleotides which binds to the 3’ end of the template DNA strand allowing DNA polymerase to add DNA nucleotides
How does DNA polymerase add DNA nucleotides?
DNA polymerase adds DNA nucleotides, using complimentary base pairing, to the deoxyribose 3’ end of the template DNA strand.
DNA polymerase can only add DNA nucleotides in one direction. What does this result in?
The formation of a leading and lagging strand
What happens on the leading strand?
On the leading strand, nucleotides are added from the 3’ end of the parental DNA molecule continuously
The primer is then replaced by DNA
How is the lagging strand replicated?
The lagging strand is replicated in fragments
How does replication of the lagging strand start?
Replication of the lagging strand starts with primer at the 3’ end and adds nucleotides discontinuously as more primer is added
What are the fragments joined together by?
The enzyme ligase
What happens after the fragments are joined together?
The primer is then replaced by DNA
What is PCR?
PCR amplifies DNA using complimentary primers for specific target sequences
In PCR, what are primers?
In PCR, primers are short strands of nucleotides which are complimentary to specific target sequences at the two ends of the region of DNA to be amplified
What are the four stages of the polymerase chain reaction (PCR)?
- DNA is heated to between 92 and 98 degrees to separate the strands
- DNA is then cooled to between 50 and 65 degrees to allow primers to bind to target sequences
- DNA is then heated to 70 and 80 degrees for heat tolerant DNA polymerase to replicate the region of DNA
- Reaped cycles of heating and cooling, amplify this region of DNA
