2.7 DNA replication, transcription and translation Flashcards
What type of process is DNA replication?
Semi-conservative
When a new double stranded DNA molecule is formed, what will each strand be?
One will be from the original template molecule
One will be newly synthesised
Why does DNA replication occur as a semi conservative process?
Because each nitrogenous base can only pair with its complementary partner
What is each new strand of DNA when it is replicated by the combined action of helicase and DNA polymerase?
Identical to the original strand separated from the template
when DNA is replicated by the combined action of helicase and DNA polymerase, what will the two semi conservative molecules have?
An identical base sequence to the original molecule
What are the three models proposed for the method of DNA replication?
Conservative model
Semi conservative model
Dispersive model
What is the conservative model?
A whole new molecule is synthesised from a DNA template which will remain unchanged
What is the semi conservative model?
Each new model has one new synthesised strand and one template strand
What is the dispersive model?
New molecules are made of segments of new and old DNA
What did Meselson and Stahl use to test the validity of the three hypothesis?
Radioactive isotopes of nitrogen
What did the results of Meselson and Stahl support?
Semi conservative model
How did Meselson and Stahl use nitrogen in their experiments?
DNA molecules were prepared using heavier nitrogen and then induced to replicate in the presence of the lighter nitrogen
In meselson and stahls experiment what was disproved after one division and why?
Conservative model as both lighter and heavier nitrogen were found
In meselson and stahls experiment what was disproved after two divisions and why?
The dispersive model as some DNA molecules had only the lighter nitrogen
What does pre existing strands do in DNA replication?
Act as templates for newly synthesised strands
What are the two enzymes that coordinate DNA replication?
Helicase and DNA polymerase
What does helicase do?
Unwinds the double helix and separates the two polynucleotide strands
How does helicase do what it does?
By breaking the hydrogen bonds that exist between the complimentary base pairs
What happens to the two newly separated polynucleotide strands?
they will act as templates for the synthesis of new complementary strands
What does DNA polymerase synthesise?
New strands from the two parental template strands
What do free deoxynucleoside triphosphates do?
Align opposite their complementary base partner
What does DNA polymerase do?
Cleaves the two excess phosphates and uses the energy released to link the nucleotide to the new strand
What is PCR?
An artificial method of replicating DNA in lab conditions
What is PCR used for?
To amplify large quantities of a specific sequence of DNA from an initial small sample
What does each reaction in PCR do?
Doubles the amount of DNA
What does PCR stand for?
Polymerase Chain Reaction
What does 30 cycles of a standard PCR sequence create?
Over 1 billion copies of DNA
Where does the PCR occur?
In a thermal cycler
What is used to control DNA replication in PCR?
variations in temperature
What are the three steps of PCR?
Denaturation
Annealing
Elongation
What is the temperature used during denaturation?
90ºC
What is the temperature used during annealing?
55ºC
What is the temperature used during elongation?
75ºC
What happens during denaturation?
DNA sample is heated to separate the two strands
What happens during annealing?
Sample is cooled to allow primers to anneal
What happens during elongation?
Sample is heated to optimal temperature for a heat tolerant polymerase to function
What enzyme is used during PCR?
Taq polymerase
Why can taq polymerase function in PCR without denaturing?
As the enzymes optimal temperature is 75ºC
What does taq polymerase do?
Extends the nucleotide chain from the primers
In PCR what are primers used for?
To select the sequence to be copied
What is transcription?
The process where an RNA sequence is produced from a DNA template
During transcription, what does RNA polymerase separate?
The DNA strands
During transcription, what does RNA synthesise?
A complementary RNA copy from one of the DNA strands
During transcription, what happens when the DNA strands are separated?
Ribonucleoside triphosphates align opposite their exposed complementary base partner
During transcription, what does RNA polymerase remove?
The additional phosphate groups
During transcription, what does RNA polymerase use the energy for?
To covalently join the nucleotide to the growing sequence
What happens once the RNA sequence has been synthesised?
RNA polymerase detaches from the DNA molecule and the double helix reforms
What is a gene?
The sequence of DNA that is transcribed into RNA
What is the antisense strand?
The strand of DNA that is transcribed
What is the antisense strand complementary to?
The RNA sequence
What is the sense strand?
The strand of DNA that is not transcribed
What is the sense strand identical to?
The RNA sequence with T instead of U
Where does transcription of genes occur?
In the nucleus
Where does the RNA move to and why?
To the cytoplasm for translation
What encodes the production of a polypeptide?
The base sequence of an mRNA molecule
What reads the mRNA sequence?
The ribosome in triplets of bases called codons
What does each codon code for?
One amino acid with a polypeptide chain
What does the order of the codons in an mRNA sequence determine?
The order of amino acids in a polypeptide chain
What is the genetic code?
Set of rules where information encoded within mRNA sequence is converted into amino acid sequences by living cells
What does the genetic code identify?
The corresponding amino acid for each codon combination
How many codon possibilities are there?
64
What does the coding region of an mRNA sequence always begins with and end with?
A start codon and an end codon
What is translation?
The process of protein synthesis where genetic information encoded in mRNA is translated into a sequence of amino acids on a polypeptide chain
During translation, what do ribosomes bind to and where?
To mRNA in the cytoplasm
During translation, how does ribosomes move along the molecule?
In a 5’ to 3’ direction until it reaches a start codon
During translation, what does anticodons on tRNA molecules do?
Align opposite appropriate codons according to complementary base pairing
During translation, what does each tRNA molecule carry?
A specific amino acid
During translation, what does ribosomes catalyse?
The formation of peptide bonds between adjacent amino acids
During translation, what does the ribosome synthesise?
A polypeptide chain
During translation, when does the ribosome stop synthesising?
When it reaches a stop codon
During translation, what happens when the ribosome reaches a stop codon?
Translation stops and the polypeptide chain is released
What are the eight key components of translation?
(Mr cat app)
Messenger RNA
Ribosome
Codons
Anticodons
Transfer RNA
Amino acids
Peptide bonds
Polypeptides
What is universal?
The genetic code
How is the genetic code universal?
Almost every living organism uses the same code
Why is genetic information transferrable between species?
As the same codons code for the same amino acids in all living things
What has the ability to transfer genes been utilised to do?
Produce human insulin in bacteria
What are the four steps to extract insulin?
The gene responsible for insulin production is extracted from a human cell
It is spliced into a plasmid vector before being inserted into a bacterial cell
The transgenic bacteria are then selected and cultures in a fermentation tank
The bacteria now produces human insulin which is harvested purified and packaged for human use
What is mRNA?
mRNA is a complementary copy of a gene and is used to deduce the gene sequence
When converting a sequence from mRNA to the original DNA code, what rules must be applied?
Cytosine is replaced with guanine and vice versa
Uracil is replaced with Adenine
Adenine is replaced with Thymine
