DNA Replication and Protein Synthesis Flashcards
Explain why DNA replication is necessary.
Mitosis and meiosis can occur without halving the genome each time
Define the term “semi-conservative replication”. (F)
DNA replication results in one old strand and one new strand present in each daughter DNA molecule
Describe the process of DNA replication in a series of bullet points. (F)
- DNA helicase separates the two strands of DNA
- activated free nucleotides are attracted to their complementary bases
- DNA polymerase joins together the lined up base pairs
- all nucleotides are joined to form two new polynucleotide chains
State the role of the enzyme DNA polymerase in DNA replication
Catalyses the formation of phosphodiester bonds between nucleotides.
State the role of the enzyme DNA helicase in DNA replication
Catalyses reactions that break the hydrogen bonds between complementary base pairs.
Outline the experimental procedure used by Meselson and Stahl to prove that DNA replicated by semi-conservative replication. (S+C)
- grew E. coli in a growth medium with N-14
- transferred to a growth medium with N-15
- centrifuged the DNA with cobalt chloride
- compared the densities of the DNA in different generations
Describe how, and explain why, DNA replication occurs by continuous replication of one strand and discontinuous replication of the other strand. (S+C)
- DNA polymerase can only travel 3’ to 5’
- DNA only unzips from one direction
- leading strand is unzipped from 3’ and can be continuously replicated
- lagging strand is unzipped from 5’ so DNA polymerase has to wait for a section to be unzipped so is discontinuously replicated
Explain the importance of DNA replication conserving genetic information with accuracy.
- may cause base sequence to change
- codes for different amino acid
- changes structure of protein
- may not function properly
Define the term “mutation”. (F)
A change in the genetic material which may affect the phenotype of the organism
Outline how the sequence of bases in DNA can code for the primary structure of a polypeptide chain. (F)
- every 3 bases is a codon
- every codon codes for an amino acid
- the order of codons determines the order of amino acids (the primary structure)
Define the term “codon”.
A three-base sequence of DNA or RNA that codes for an amino acid.
Define the term “gene”.
A section of DNA that contains the complete sequence of bases to code for a protein.
Define the term “triplet code” in relation to the genetic code. (F)
- three bases form a codon
- each codon codes for an amino acid
Define the term “non-overlapping” in relation to the genetic code. (F)
- read from base 1
- triplets of bases read “in frame”
- each codon is read separately to each other
Define the term “degenerate” in relation to the genetic code. (F)
- amino acids can be coded for by more than one codon
Define the term “universal” in relation to the genetic code. (F)
- all organisms use the same code
Explain why the genetic code is a triplet code.
- 4 different bases
- if every codon was 1 base, only 4 amino acids can be coded for
- if every codon was 2 bases, only 16 amino acids can be coded for
- as the codon is 3 bases, 64 bases can be coded for
Explain the value of the genetic code being non-overlapping.
- can only be read in one way
- sequence of amino acids will be same each time
Explain the reason for the genetic code being degenerate.
- there are more codons present than amino acids
Describe what is meant by a “start codon”.
The sequence of amino acids that signify the start of a gene.
Describe what is meant by a “stop codon”.
The sequence of amino acids that signify the end of a gene.
Outline how mutations can alter the structure of a protein.
- can alter the genetic code to produce a different amino acid
- this affects the primary structure
- different R-group so will form different bonds
- this affects the secondary, tertiary and quaternary structures
Define the term “transcription”.
The process of copying sections of DNA base sequence to produce smaller molecules of mRNA, which can be transported out of the nucleus via the nuclear pores to the site of protein synthesis.
State the three types of RNA.
- messenger RNA (mRNA)
- ribosomal RNA (rRNA)
- transfer RNA (tRNA)
Describe the structure of mRNA. (F)
- single strand
- short
- uracil instead of thymine
Describe the structure of rRNA. (F)
- complexes with proteins
- forms two subunits (large and small)
Describe the structure of tRNA. (F)
- strand of RNA folded into hairpin shape
- anticodon is at one end of molecule
- carry amino acid corresponding to codon
Describe the function of mRNA. (F)
- allows genetic information to leave the nucleus
- codes for the protein
Describe the function of rRNA. (F)
- forms ribosome
- maintains structural stability of protein synthesis
- biochemical role in catalysing the reaction
Describe the function of tRNA. (F)
- brings amino acid to ribosome to form primary structure of protein
Describe the process of transcription in a series of bullet points. (F)
- hydrogen bonds broken between DNA strands
- free RNA nucleotides base pair with complementary bases exposed on antisense strand
- RNA polymerase forms phosphodiester bonds between RNA nucleotides
Describe the process of transcription in a series of bullet points. (F)
- hydrogen bonds broken between DNA strands
- free RNA nucleotides base pair with complementary bases exposed on antisense strand
- RNA polymerase forms phosphodiester bonds between RNA nucleotides
- stops at end of gene
- mRNA detaches from DNA and leaves nucleus through nuclear pore
Define the terms “sense strand”.
The strand of DNA that runs 5’ to 3’ and contains the genetic code for a protein.
Define the terms “template strand”.
The antisense strand of DNA that acts as a template during transcription so the complementary RNA strand formed carries the same code for a protein as the DNA sense strand.
Describe the structure of a ribosome.
- large and small subunit
- composed of equal amounts of rRNA and protein
Describe the process of translation in a series of bullet points. (F)
- mRNA attaches to a ribosome via its start codon
- tRNA with complementary anticodon hydrogen bonds to the start codon
- second codon also attracts its complementary anticodon
- a peptide bond forms between the amino acids
- the ribosome moves along the mRNA by one codon
- the first tRNA leaves the ribosome
- another tRNA is attracted to the new exposed codon
- process is repeated to build up a polypeptide chain
- ribosome stops when it comes to a stop codon
