Unit 1.2 Structure & replication of DNA Flashcards
The structure of DNA
Double stranded helix
What does DNA carry
The genetic information for making proteins
What are the four bases that make up the genetic code
Adenine, cytosine, guanine, & thymine
What is the complementary base pair rule
Adenine always pairs with Thymine, Cytosine always pairs with Guanine
What does each molecule of DNA consist of
2 strands, where each strand is made up of repeating units called nucleotides
What does each DNA nucleotide consist of
Deoxyribose sugar, phosphate & a base
What type of bond forms between the phosphate of one nucleotide & the deoxyribose sugar of the next nucleotide. What does this create
Strong chemical bonds that are not easily broken, this creates the sugar-phosphate backbone
How many different types of nucleotides are there and why
4 as there are 4 different types of bases
What are the base pairs joined together by
Weak hydrogen bonds that are easily broken
What is it called when the 2 strands of DNA run in opposite directions
Anti-parallel
Why is DNA unique
It is able to direct its own replication & reproduce itself exactly
Why is it important that DNA replication takes place before a cell undergoes mitosis
It ensures each new cell has the correct chromosome complement
What are the 7 stages of DNA replication
1- DNA double helix unwinds
2- Weak hydrogen bonds between the bases are broken to form 2 template strands
3- To initiate replication, a primer binds to each template strand at the 3’ end
4- DNA polymerase adds DNA nucleotides (using complementary base pairing) to the 3’ end of the new DNA strand that is forming
5- As nucleotides are added, weak hydrogen bonds form between the base pairs
6- Strong chemical bonds form between the nucleotides of the new strand (forming a sugar-phosphate backbone)
7- Newly formed daughter DNA fold back to double helix
What is each DNA molecule known as after replication
Semi-conservative
What does semi-conservative mean
Each DNA molecule contains one strand from the original parent & one newly synthesised strand
What is the only direction DNA polymerase can add DNA nucleotides
They can only be added to the 3’ end
What DNA strand is replicated continuously
The leading strand
What DNA strand is replicated in fragments
The lagging strand
What enzyme joins the fragments of the lagging strand together
Ligase
What are the 5 requirements for DNA replication
- DNA
- Primers
- DNA nucleotides
- Enzymes
- ATP
What chemical group is found at the 5’ end of the DNA strand
Phosphate
What is required when studying the genome
Millions of identical fragments of DNA need to be created
How are millions of identical fragments of DNA created
Through the process of PCR
What does PCR produce
Many copies of a specific section of DNA
What does in vitro mean
In the lab
What does PCR use to amplify DNA
Complementary primers for specific target sequences
What are primers in PCR
Short strands of nucleotides which are complementary to specific target sequences at the 2 ends of the region of DNA to be amplified
First stage of PCR
Melting: DNA is heated (92-98°C) to break the hydrogen bonds, allowing the original DNA strands to be separated
Second stage of PCR
Annealing: Sample is cooled (50-65°C). Allows complementary primers to bind to target sequences at the start of each strand
Third stage of PCR
Extension: Sample is heated (70-80°C) for heat-tolerant DNA polymerase to replicate the region of DNA & adds DNA nucleotides to the 3’ end of the new strands
How many identical copies of DNA are made after the first cycle of PCR
Two
What are the 6 requirements for PCR
1- Original DNA sample/template
2- A stock of each of the 4 DNA nucleotides
3- DNA primers
4- Heat-tolerant DNA polymerase (enzyme)
5- Buffer solutions
6- A thermal cycler
What do buffer solutions do
maintain optimum pH of the enzyme
What is a thermal cycler
An automated reaction vessel
What can PCR be useful for
Solving crimes, settling paternity disputes & diagnosing genetic disorders
What does amplification mean
The number of original molecules has doubled
What/ whose DNA samples do forensic scientists take to solve crime
DNA samples from the crime scene, the suspect(s) and the victim
What then happens to the DNA samples once taken (solving crimes)
The components of the samples are separated using gel electrophoresis & compared to identify the criminal
What is gel electrophoresis
A technique used to separate macromolecules such as DNA
Describe how gel electrophoresis works
DNA samples are placed in wells of a gel.
An electric current is applied to the gel & since DNA molecules are negatively charged they move towards the positive end of the gel.
As the DNA fragments are different sized the smaller particles move further in the gel thus separating out the DNA fragments
How much DNA does an individual inherit from each of their parents
50%
