8. DNA, Genes and Protein Synthesis Flashcards
What is a gene?
A section of DNA containing the codedInformation for making polypeptides and functional RNA.
what is the minimum number of bases that code for for each amino acid?
Three
what is a degenerate code?
Most amino acids are coded for by more than one triplet.
The start of a DNA sequence that codes for a polypeptide is always the same triplet, what is this triplet?
Methionine/ AUG
what does it mean if the genetic code is non-overlapping?
Each base in the sequence is only read once, e.g. 123 456
What does it mean if the genetic code is universal?
Each triplet codes for the same amino acid in all organisms.
what are exons?
Coding sequences.
What are introns?
Non coding sequences.
Calculate how many bases are required for a chain of six consecutive amino acids?
18
Explain how a change in one base along the DNA molecule may result in an enzyme becoming non-functional
A different base might code for a different amino acid. The sequence of amino acids in the polypeptide produced will be different. This change in the primary structure of a protein might result in a different tertiary structure. The enzyme shape will be different and may not fit the substrate. The enzyme substrate complex cannot be formed and so the enzyme is non-functional.
Describe the differences in the DNA of prokaryotic cells and eukaryotic cells?
In prokaryotic cells the DNA molecules are shorter, form a circle and are not associated with the protein molecules; therefore they do not have a chromosomes.
In eukaryotic cells DNA molecules are longer, linear rather than a circle, and occur in association with proteins called histones to form structures called chromosomes.
State the function of the protein found in chromosomes.
Proteins called histones fix the DNA into position.
Describe the structure of a gene?
Chromosomes only visible when a cell is dividing. Chromosomes appear as two threads joined by a single point. Each thread is called a chromatid and are attached to the centromere. The length of DNA found in each cell is highly coiled. The double helix is wound around histones to fix it in position. The DNA-histone complex is coiled. The coil is further coiled before being packaged into the chromosome. This allows a considerable length of DNA to be condensed into a single chromosome.
what is a homologous pair of chromosomes?
A pair of chromosomes one maternal and one paternal, that have the same gene loci and therefore determine the same features. They are not necessarily identical, however, as individual alleles of the same gene may vary, e.g. one chromosome may carry the allele of blue eyes and the other for brown eyes. Homologous chromosomes are capable of pairing during meiosis.
What is an allele?
One number of alternative forms of a gene.
What is the role of mRNA?
Transfers the DNA code from the nucleus to the cytoplasm and acts as a type of messenger. It is small enough to leave the nucleus through the nuclear pore and enter the cytoplasm where the coded information that it contains is used to determine the sequence of amino acids and the proteins which are synthesised there.
Define codon
The sequence of three bases on mRNA that codes for a single amino acid.
Define ‘genome’
The complete set of genes in a cell including those in mitochondria and chloroplasts
Define ‘proteome’?
The full range of proteins produced by the genome.
State three ways in which the molecular structure of RNA differs from the structure of DNA.
RNA is smaller than DNA, RNA is normally a single strand and DNA is a double helix, the sugar in RNA is ribose while the sugar in DNA is deoxyribose, in RNA the base uracil replaces the base thymine found in DNA.
Describe the structure of mRNA
mRNA is a long strand that is arranged in a single helix. The base sequence of mRNA is determined by the sequence of bases on a length of DNA in transcription. It possesses information in the form of codons, which determine the amino acid sequence of a specific polypeptide.
Describe the structure of tRNA
tRNA is a relatively small molecule that is made up of around 80 nucleotides. It is a single-stranded chain folded into a cloverleaf shape, with one end of the chain extending beyond the other, this is the part of the tRNA molecule to which an amino acid can easily attach. Opposite end of the tRNA molecule is a sequence of three other organic bases, known as the anticodon. Each tRNA is specific to one amino acid and has an anti codon that is specific to that amino acid.
Distinguish between a codon and an anticodon
A codon is the triplet of bases on mRNA that codes for an amino acid. An anticodon is the triplet of bases on tRNA that is complimentary to a codon.
Describe the process of transcription
An enzyme acts on a specific region of DNA causing the two strands to separate and expose the nucleotide bases.
The nucleotide bases on the two DNA strands, known as the template strand, pair with the complementary nucleotides from the pool which is present in the nucleus.The enzyme RNA polymerase then moves along the strand and joins the nucleotides together to form a pre-mRNA molecule.
When the RNA polymerase reaches a particular sequence of the bases on the DNA that it recognises as a stop triplet code, it detaches and the production of pre-mRNA is complete.
