Protein Synthesis Flashcards
Exons
sections of a gene that code for the sequence of amino acids in a polypeptide
Introns
DNA base sequences that do not code for any amino acids in the polypeptide
Eukaryotic Vs Prokaryotic DNA
Eukaryotic: linear, associated with histones (proteins), introns
Prokaryotic: circular, not associated with histones, no introns
mRNA Vs tRNA
mRNA:
-single stranded
-shorter than DNA
-3 bases=codon
-uracil
-no hydrogen bonds
tRNA:
-single stranded
-about 75 nucleotides
-cloverleaf shape
-held by hydrogen bonds
-3 bases=anticodon
function of tRNA
carry a specific amino acid into a ribosome, so protein synthesis can occur
Genome definition
complete set of genes in a cell
Proteome definition
full range of proteins cell is able to produce
Loci definition
position of a gene within chromosome
Allele definition
different versions of a gene
Gene definition
DNA base sequence that codes for a single polypeptide
What does protein synthesis involve?
-Protein synthesis involves the nucleic acids DNA and RNA. -Both are polymers made up by many nucleotides
-joined together by phosphodiester bonds
-through condensation reactions
DNA Vs mRNA
DNA:
-double stranded
-longER
-Thymine in DNA
-Deoxyribose in DNA
-has hydrogen bonds
-has introns
mRNA:
-single stranded
-shortER
-Replaced with uracil in RNA
-Ribose in RNA
-doesn’t have hydrogen bonds
-doesn’t have introns
Where does transcription occur
prokaryotes- occurs in cytoplasm
eukaryotes- occurs in nucleus
Transcription
- DNA Helicase breaks hydrogen bonds so strands separate;
- Only one DNA strand acts as template;
- RNA nucleotides attracted to exposed bases;
- Attraction according to base pairing rule A-U, C-G, T-A;
- RNA polymerase joins RNA nucleotides together forming phosphodiester bonds through condensation reactions;
- Pre-mRNA spliced to remove introns (Eukaryotes).
- mRNA passes out of nuclear pore into ribosome
Where does translation occur?
cytoplasm at a ribosome
Translation
- mRNA attaches to ribosomes
- tRNA anticodons bind to complementary mRNA codons;
- tRNA brings a specific amino acid;
- Amino acids join by peptide bonds;
- Amino acids join together with the use of ATP;
- tRNA released after amino acid joined to polypeptide;
- The ribosome moves along the mRNA to form the polypeptide;
The Genetic Code
Universal- the same 3 bases on mRNA / DNA code for the same amino acids in all organisms
Non-overlapping –Each base is only part of 1 triplet / codon
Degenerate- More than one triplet/codon codes for an amino acid
(The first two bases are the most important when coding for amino acids.)
What is a gene mutation
A gene 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 a gene coding for an enzyme
could lead to the production of a non-functional enzyme. Explain how
- Change in base sequence of DNA
- Change in amino acid sequence / primary structure
- Change in hydrogen/ionic/ disulphide bonds;
- Change in the tertiary structure
- No enzyme-substrate complexes form;
Not all mutations in the nucleotide sequence of a gene cause a change in the structure of a polypeptide. Give two reasons why.
- Triplets code for same amino acid
- Occurs in introns /non-coding sequence
Substitution Mutations
substitution in third base= silent mutation, mutation does not change the amino acid coded for, so will have no effect on the polypeptide chain (degenerate)
substitution in first/second base= change amino acid sequence, alters sequence of amino acids on the polypeptide chain, so may alter its specific tertiary structure
Addition & Deletion Mutations
- frame shift
- different sequence of triplets in DNA
- different primary structure of polypeptide
- different position of R groups
- different tertiary structure
(mutation towards end=lesser effect)
How do mutations occur?
occur spontaneously during DNA replication. They are natural, and cause permanent changes to the DNA which is passed on to future generations. They occur at a set rate
-Mutations are responsible for the genetic diversity of populations both in the forces of natural selection and in speciation.
-can be advantageous, disadvantageous or have neutral effects.
-Mutations in gametes can often prove fatal
Mutagenic Agents
Mutagenic agents increase the rate of spontaneous mutation
- High energy ionising radiation (X rays)
- DNA reactive chemicals such as benzene
- Biological agents such as some viruses and bacteria.
Chromosomal Mutations
-during meiosis the daughter cell produced contains too many chromosome
-pair of homologous chromosomes fail to separate in metaphase 1 or sister chromatids fail to separate in metaphase 2
-known as chromosome non-disjunction
Inversion Mutations
when a segment of bases is reversed end to end
Duplication Mutations
A doubling of a part of a chromosome, of an entire chromosome, or even the whole genome
Translocation Mutations
when groups of base pairs relocate from one area of the genome to another, usually between non-homologous chromosomes.
What is natural selection?
Process by which organisms that are better adapted to their environment survive and reproduce in greater numbers, resulting in the increase of the frequency of the advantageous allele within the population
Explain how selection occurs in living organisms
- Variation due to mutation;
- Different selection pressures;
- Selection for advantageous allele;
- Selected organisms survive and reproduce;
- Leads to change in allele frequency;
- Occurs over a long period of time;
Genetic Diversity Definition
the number of different alleles of genes in a population
What is phenotype determined by?
the genotype and its interaction with the environment
Stabilising Selection
- Occurs in all populations where environment is stable.
- Selection pressure at both ends of distribution.
- Favours the average.
- Tends to eliminate extremes.
- Reduces variability
- Reduces opportunity for evolutionary change.
Directional Selection
- Mean in population represents optimum phenotype for existing conditions
- Environmental change may produce new selection pressure that favours an extreme phenotype
- Changed conditions, favour allele combination necessary for survival
- Some organisms will possess the new optimum phenotype (allele combination)
- Over time, selection means this allele combination will predominate and the mean phenotype will shift.
Disruptive Selection
- Is the opposite of stabilising selection
- Environment has selection pressures that favour 2 extreme phenotypes
- When conditions change the optimum phenotypes necessary for survival will also change
- Some organisms will possess the new extreme optimum phenotypes
- Over time selection means these 2 extremes will dominate and the mean will shift in both directions (towards extremes)
- It is the least common type of selection but it is the most important in evolution
Dilution Plating Technique
add 1ml of sample into 9ml broth and mix to form 1/10 dilution. add 1ml of 1/10 into fresh 9ml sample broth, mix to form 1/100 dilution…
Counting Bacteria Calculations
Counting bacteria after given number of replications:
2^n (n= number of divisions)
(if starting amount 100=100x2^n)
Finding number of divisions:
log2n (n=number of bacteria)
How to count bacteria
-counting cells directly
-diluting the original sample and then counting cell numbers
-turbidity (cloudiness) of the culture with colorimetry
Direct cell counts may be divided into
- Total counts = which include both living cells and dead cells
- Viable counts = which count living cells only
The student looked at cells in a 1 in 10 dilution during his preliminary work. He decided not to use this dilution to determine the number of cells in the undiluted liquid culture.
Suggest an explanation for the student’s decision.
- Count unlikely to be accurate / repeatable / reproducible / reliable;
- Because too many cells; OR Because cells overlapping / not spread out;
Define ‘non-coding base sequences’ and describe where the non-coding multiple repeats are positioned in the genome.
- DNA that does not code for protein/polypeptides OR DNA that does not code for (sequences of) amino acids OR DNA that does not code for tRNA/rRNA;
- (Positioned) between genes
Define ‘gene mutation’ and explain how a gene mutation can have:
* no effect on an individual
* a positive effect on an individual.
- Change in the base sequence of DNA
- Results in the formation of new allele;
(Has no effect because)
3. Genetic code is degenerate (so amino acid sequence may not change); OR
Mutation is in an intron (so amino acid sequence may not change);
Accept description of ‘degenerate’, eg some amino acids have more than one triplet/codon.
(Has positive effect because)
6. Results in change in polypeptide that positively changes the properties (of the protein)
7. May result in increased survival (chances);
