Protein Synthesis Flashcards
(12 cards)
Describe two differences between the structure of a tRNA molecule and the structure of an
mRNA molecule.
tRNA is a clover leaf shape, mRNA is linear
tRNA has an amino acid binding site, mRNA does not
In a eukaryotic cell, the structure of the mRNA used in translation is different from the
structure of the pre-mRNA produced by transcription.
Describe and explain a difference in the structure of these mRNA molecules.
mRNA has fewer nucleotides
pre-mRNA has exons and introns
because of splicing
Describe how one amino acid is added to a polypeptide that is being formed at a ribosome
during translation.
tRNA brings the specific amino acid to ribosome
anticodon on tRNA binds to codon to mRNA
amino acids join together by condensation reaction by ATP
amino acids join together to form a peptide bond using ATP
Crystallin is a structural protein found in the human eye. An inherited disease that leads to
blindness is caused by changes in properties of crystallin. The replacement of the amino
acid Arg with the amino acid Gly causes these changes.
Use information in Table 1 to suggest why this amino acid replacement changes the
properties of crystallin
Hydrogen bonds form instead of ionic bonds
This changes the tertiary structure of crystallin
Describe how mRNA is produced from an exposed template strand of DNA.
Do not include DNA helicase or splicing in your answer.
free RNA nucleotides form complementary base pairs
forming phosphodiester bonds
catalysed by RNA polymerase
Define the term exon.
a nucleotide/base that codes for a polypeptide/sequence of amino acid
A mutation in the nucleotide sequence shown in Figure 1 resulted in the following amino acid sequence.
A student concluded that the mutation involved the addition of one nucleotide within the sequence shown Figure 1.
Does information in this question support the student’s
conclusion? Give reasons for your answer.
G to C (in the second codon/for Glycine)
OR
CGT to CCT (in second codon/for Glycine);
(So), substitution (not addition mutation);
Describe how mRNA is formed by transcription in eukaryotes.
Hydrogen bonds between DNA bases break
Only one DNA strand acts as a template
Free RNA nucleotides align by complementary base pairing
in RNA uracil is replaced with Adenine in DNA
RNA polymerase joins adjacent RNA nucleotides together by phosphodiester bonds
pre-mRNA is then spliced to form mRNA
Describe how a polypeptide is formed by translation of mRNA.
mRNA associates with a ribosome
tRNA brings specific amino acid to ribosome
anticodon to tRNA binds to codon on mRNA
amino acids join together by condensation reaction by ATP
amino acids join together to form a peptide bond by ATP
peptide bond is formed between amino acids
tRNA is released then the ribosome is moved along the mRNA to form a polypeptide
Define ‘gene mutation’ and explain how a gene mutation can have:
* no effect on an individual
* a positive effect on an individual.
NO EFFECT
it is a change in the base sequence of DNA
it results in the formation of a new allele
it has no effect because the genetic code is degenerate
amino acid changes but no effect on tertiary structure
POSITIVE EFFECT
no allele is recessive which results a change in polypeptide that positively changes the properties
this can increase reproduction
Starting with mRNA in the cytoplasm, describe how translation leads to the production of a
polypeptide.
Do not include descriptions of transcription and splicing in your answer.
mRNA associates with a ribosome/ribosome attaches to mRNA
ribosome moves to find the start codon
tRNA brings specific amino acid to ribosome
anticodon on tRNA complementary to codon on mRNA
Ribosome moves along to next codon
process is repeated amino acids join to form a peptide bond via condensation reaction by ATP to form a polypeptide
Deletion of the sixth base (G) in the sequence shown in the diagram above would change
the nature of the protein produced but substitution of the same base would not. Use the
information in the table and your own knowledge to explain why.
Substitution would result in CCA / CCC / CCU;
(All) code for same amino acid / proline;
Deletion would cause frame shift / change in all following codons / change next
codon from UAC to ACC.
