Chapter 3 DNA Replication and Gene Expression Flashcards
Why is DNA a replication called semi conservative?
Each of the two new DNA molecules contain one of the original polynucleotide DNA strands, making it semi conservative
What are the basic stages of DNA replication?
DNA helicase catalyses the breakdown of hydrogen bonds between bases, caused the UNZIPPING and UNWINDING of the DNA double helix
Free DNA nucleotides are activated, attracted to their complimentary base pair, as the DNA helicase continues to unzip the DNA
For the 3’ to 5’ strand, DNA polymerase attaches to the hydroxyl and catalyses the formation of phosphodiester bonds continuously
For the 5’ to 3’ strand, the DNA polymerase must work backwards at multiple points, producing Okazaki fragments in discontinuous replications. These fragments are joined together by DNA ligase
Two identical DNA molecules are formed
What direction can DNA polymerase move in?
3’ to 5’, attaching to the OH only
What is a mutation? Why is DNA said to be universal?
A mutation is a change in the base sequence of DNA caused by random and spontaneous errors during replication
It is universal as all living organisms contains the same basic components of DNA
What is genetic code? How does it work?
Genetic code is the idea that the sequence of the bases in DNA act as template for the sequence of amino acids synthesised
Each 3 bases codes for one amino acid, a codon
What does degenerate code mean? What is non overlapping code?
More than one triplet code/ codon codes for the same amino acid. Each base is part of only one codon, not overlapping
Outline the process of transcription
The DNA molecule unzips at a gene, controlled by helicase enzymes, breaking hydrogen bonds between bases
The sense strand (5’ to 3’) contains the base sequence for the protein.
The antisense strand (3’ to 5’) acts as a template for free mRNA nucleotides to form complementary bases with the exposed mRNA nucleotides, producing effectively the sense strand 5’ to 3’.
RNA polymerase (works in the 5’ to 3’ direction) catalyses the formation of phosphodiester bonds between the mRNA nucleotides
The mRNA strands detaches from the DNA strand, leaving the nucleus via the nuclear pore. The DNA double helix reforms
Outline the process of translation
The ribosomal subunits bind to the mRNA molecule, reading the bases in triplets called codons.
Each codon correspond to a tRNA loop anticodon, and so a corresponding amino acid.
As the ribosome moves along the mRNA molecule, the amino acid is transferred to the polypeptide chain by forming peptide bonds to the next amino acid . The tRNA molecule is then released and replaced by the next.
At the termination codon, the polypeptide is released and folds into a protein.
How does the structure of DNA enable it to undergo semi-conservative replication?
2 DNA contains two polynucleotide strands, both of them can act as templates during replication
Hydrogen bonds between bases are easily broken/reformed
Complimentary base pairing, 2 hydrogen bonds between A =T and 3 between C—G
Purines can only bond to pyrimidines due to their size differences
Which enzymes are used in transcription compared to DNA replication?
Both use helicase enzymes but transcription uses RNA helicase whilst replication used DNA helicase
