Protein Synthesis and Selection Flashcards
DNA Structure:
- A double helix consisting of two polynucleotide strands
- Each nucleotide is formed from deoxyribose, a phosphate group and a nitrogenous base
- Both polynucleotides are made by joining adjacent DNA nucleotides by phosphodiester bonds (through condensation reactions, catalysed by DNA polymerase)
- The two polynucleotide strands are held together by hydrogen bonds between complementary basis (Adenine to Thymine and Guanine to Cytosine)
Eukaryotic DNA:
-Linear
-Associated with histones
-Contains introns
Prokaryotic DNA:
-Circular
-Not associated with histones
-Does not contain introns
Introns are non-coding base sequences of DNA found within a gene
mRNA
· This is a single stranded polynucleotide chain.
· It is a complementary copy of a single gene, from the TEMPLATE strand of DNA.
· mRNA’s length will vary depending upon the number of bases that make up the gene, so it is much shorter than DNA.
· The sequence of bases on the mRNA are complementary to the sequence of bases of the gene it is copying.
· Complementary bases pair rules: Guanine with Cytosine and Adenine with Uracil
Contrasting DNA and mRNA:
-DNA is double stranded whereas RNA is single stranded
-DNA is longer whereas RNA is shorter
-Thymine in DNA whereas Replaced with uracil in RNA
-Deoxyribose in DNA whereas Ribose in RNA
-DNA has hydrogen bonds whereas mRNA doesn’t have hydrogen bonds
-DNA has introns whereas mRNA doesn’t have introns
tRNA
-single stranded
-cloverleaf structure held by hydrogen bonds
-It has an amino acid attachment site where only a specific amino acid binds
-it also has a region of 3 bases known as an anticodon.
-anticodon is specific to the amino acid carried by the tRNA and is complementary to the codon on the mRNA.
-The role of the tRNA molecules is to carry a specific amino acid to the RIBOSOME [site of protein synthesis]
Genome – complete set of genes in a cell
Proteome – full range of proteins that a cell is able to produce
Loci – position of a gene within chromosome
Allele – a different version / form of a gene
Gene- a DNA base sequence that codes for a sequence of amino acids in a polypeptide
Exon:
Base sequence coding for a
polypeptide
Transcription:
1. (DNA Helicase) Hydrogen bonds are broken so strands separate
2. Only one DNA strand acts as template
3. RNA nucleotides attracted to exposed bases
4. (Attraction) according to base pairing rule Adenine-Uracil, Cytosine-Guanine
5. RNA polymerase joins (RNA) nucleotides together forming phosphodiester bonds through condensation reactions
6. Pre-mRNA spliced to remove introns (in Eukaryotes)
Translation:
1. mRNA binds to ribosome
2. Ribosome finds the START codon
3. Idea of two codons/binding sites
4. (Allows) tRNA with complementary anticodons to bind/associate with codon
5. (Catalyses) formation of peptide bond between amino acids (held by tRNA molecules) using energy from ATP
6. tRNA released as Ribosome moves along (mRNA to the next codon)/translocation described
7. Ribosome releases polypeptide into RER when the STOP codon is reached
Describe the role of ATP in
the process of translation in
protein synthesis
- Releases energy;
- (So) peptide bonds form between amino acids OR (So) amino acid joins to tRNA;
The Genetic Code is:
Universal – the same 3 bases on mRNA (codon) / DNA (triplets) code for the same amino acids in all organisms.
The Genetic Code is:
Non-overlapping - A base from one triplet cannot be used in an adjacent triplet
The Genetic Code is:
Degenerate - more than one codon codes for an amino acid.
There are 20 amino acids and 64 combinations of triplets / codons
A mutation is any change to the DNA base sequence
A gene mutation (single-point mutation) is a change to a single base in the DNA base sequence of a gene. These mutations occur randomly and happen spontaneously
A mutation in DNA may result in a change in the PRIMARY STRUCTURE OF POLYPEPTIDES, sequence of amino acids in the polypeptide chain.
CONSEQUENCE:
· May alter the SECONDARY STRUCTURE (change the position of the weak Hydrogen bonds affecting the alpha helices and beta-pleated sheets)
· May alter the TERTIARY STRUCTURE (change the position of the weak Hydrogen, Ionic bonds between the R groups of amino acids and the Disulphide bonds) and may alter the BINDING site or ACTIVE site of enzymes and make the protein non-functional.
A mutation in a gene coding
for an enzyme could lead to the production of a non-functional enzyme
Explain how
- Change in base sequence (of DNA/gene);
- Change in amino acid sequence / primary structure (of enzyme);
- Change in hydrogen/ionic/ disulphide bonds;
- Change in the tertiary structure/active site (of enzyme);
- Substrate not complementary/cannot bind (to enzyme / active site) / no enzyme-substrate complexes form;
Substitution mutation:
When one nucleotide in the DNA sequence is replaced by another
A substitution may not always be harmful as the substituted nucleotide may code in that triplet for the same amino acid.
This is known as a silent mutation, where the mutation does not change the amino acid coded for, so will have no effect on the polypeptide chain
If a mutation causes a triplet to code for a STOP codon, this will cause the growing polypeptide chain to terminate prematurely and may not be able to perform it’s intended function (depending upon how early the termination occurred)