Core component 5 - Replication And Synthesis Flashcards
What is the theory of semi-conservative replication?
When one parental double helix separates into two strands and each of these strands acts as a template forming a new molecule
What are the characteristics of the genetic code?
1) Three bases encode each amino acid
2) More than one triplet code can code for one amino acid - degenerate
3) Code is punctuated - stop codons
4) Universal - same triplet code for same amino acid
5) Non overlapping
It is for the production of polypeptides
How does DNA replicate ?
1) Enzyme helicase breaks hydrogen bonds and unzips and unwinds the DNA exposing unpaired bases
2) These strands act as template and DNA polymerase then forms bonds between adjacent nucleotides in the new strands of the new DNA being formed
What is the difference between eukaryotic genes and prokaryotic genes?
Eukaryotic genes are usually discontinuous genes with coding exons and non-coding introns (cannot be translated into proteins)
Prokaryotic genes are usually continuous, lacking non-coding sequences and direct the synthesis of polypeptides
What is post-transcriptional modification ?
It’s where introns in pre-mRNA are cut out by endonuclease and the sequences left are the exons which are joined together by ligase.
Describe the process of transcription
1) DNA helicase breaks hydrogen bonds - strands unwind
2) RNA polymerase binds to DNA and DNA acts as template
3) Free RNA nucleotides bind to DNA -complementary base pairing
4) RNA polymerase separates from template strand when it reaches stop sequence
5) MRNA synthesised and leaves nucleus through nuclear pore
What are the two subunits in a ribosome used for ?
The larger subunit has two sites for attachment of tRNA molecules (two associated at one time)
The smaller subunit binds to mRNA
What is the process of translation?
1) Ribosome attaches to a start codon on mRNA
2) first tRNA binds with an anticodon complementary to the first codon on the mRNA
3) Ribosome moves along the mRNA molecule one codon at a time
4) Two tRNA bind to the ribosomes at one time
5) Each tRNA molecule carries its own amino acid
6) Peptide bonds form between amino acids - requires ATP
7) This continues until a stop codon is reached
How does the anticodon on the tRNA determine which amino acid the tRNA molecule carries?
The base sequence on the anticodon, will cause an amino acid to attach. This anticodon pairs with a codon on mRNA (complementary) and the bases on the mRNA are complementary to a sequence on the DNA.
One gene - one enzyme hypothesis
One gene - one protein
One gene - one polypeptide hypothesis
Experiments showed that radiation damage to DNA prevented a single enzyme from being made in a fungus: one gene - one enzyme
Because enzymes are a protein this led to the idea of a one gene-one protein hypothesis.
However many proteins contain more than one polypeptide leading to the one gene-one polypeptide hypothesis
How are proteins modified?
Polypeptides can be further modified by the addition of carbohydrates, lipids or phosphates
Polypeptides can be combined
This is post-translational modification so they can function
What is the triplet code for amino acids?
Amino acids are coded for by triplets of bases in the DNA, DNA is transcribed to produce codons in mRNA and translated to produce a sequence of amino acids
