Genetic Information Flashcards
(13 cards)
What is a gene
A section of DNA that contains coded information for making polypeptides and functional RNA
What evidence supports the theory that at least 3 bases code for each amino acid?
- 20 different amino acids regularly occur in proteins.
- 4 different bases are present in DNA.
- Each amino acid must have its own code of bases on the DNA sequence.
- If each base coded for a different amino acid, only 4 different amino acids would exist.
- Using a pair of bases, 16 different codes are possible which is not enough.
- Using 3 bases, 64 are possible, suggesting that more than one triplet can code for 1 amino acid.
Describe the structure of a chromosome
Chromosomes are only visible when a cell is dividing. They appear as 2 threads (each called a chromatid) joined at a single point (a centromere). The DNA in chromosomes is held by histones. The DNA is highly coiled and folded.
What is the term used to describe a pair of chromosomes that carry the same genes but not necessarily the same alles of those genes?
Homologous chromosomes
What are alleles
An alternative form of a gene (variation of a particular gene).
What is mRNA and its function?
Messenger RNA - acts as a template for protein synthesis.
What is tRNA and its function?
Transfer RNA - carries amino acids to the ribosomes. Used in translation, binds to codons on the template strand.
Describe the process of protein synthesis
Transcription:
- DNA helicase unwinds and unzips a section of DNA that codes for the required protein by breaking hydrogen bonds between complimentary bases.
- The template strand is then exposed, free RNA nucleotides bind to their complimentary base pairs and form temporary hydrogen bonds.
- RNA polymerase creates pre-mRNA by creating phosphodiester bonds between nucleotides.
- Pre-mRNA is then spliced to remove intros, creating mRNA which then leaves the nuclear pore and travels to the ribosome.
Translation:
- tRNA molecules in a clover-like shape with an amino acid attached bind to condons on the mRNA strand.
- Amino acids form peptide bonds between them then disconnect from tRNA molecule to form sequence of amino acids (protein).
Mutation Definition
Any change to the quantity or the base sequence of the DNA of an organism.
Definition of a gene mutation
Any change to one or more nucleotide bases resulting in a change in genotype.
Describe what happens in a mutation involving the substitution of bases.
Substitution of bases is a type of gene mutation where a nucleotide in a DNA molecule is replaced by another nucleotide that has a different base.
This type of mutation will have no effect if the new triplet still codes for the same amino acid due to the degenerate nature of genetic code. However if it codes for a different amino acid than before, it could change the shape and therefore function of the resulting polypeptide. This can have large impacts on enzymes.
Describe what happens in a mutation involving the deletion of bases.
Deletion of bases is a type of genetic mutation where a nucleotide is lost from the normal DNA sequence. This can have considerable effects as the entire sequence for the polypeptide would be read differently as all bases would be shifted to the left by one base. This is because based are read in triplets.
Describe what happens in a chromosome mutation.
A chromosome mutation describes a change to the structure or number of whole chromosomes.
Chngee in whole sets of chromosomes occur when organisms have 3 or more sets of chromosomes rather than 2. This is called polyploidy and occurs mostly in plants.
Changes in the number of chromosomes can occur when homologous pairs of chromosomes do not seperate during meiosis. This is known as non-disjunction and usually results in a gamete having either one more or one fewer chromosome.
