DNA - The Genetic Code Flashcards
Where is the genetic material stored?
In the nucleus of a cell.
What are genes? [1 mark]
A short section of DNA.
Each gene codes for a specific protein.
What is DNA?
A polymer of nucleotides wound in a double helix structure.
What is a genome?
The entire genetic information/material of an organism.
What can mutations in DNA cause?
A different amino acid being produced - changes tertiary structure of protein - changes function of protein.
State the positive outcomes of knowing the whole human genome [2 marks]
> Can search for genes linked to disease.
> Understand & treat inherited disorders.
> Tracing migration patterns.
What is an exon?
A region of the genome that ends up within an mRNA molecule.
They are the CODING sequences in DNA.
What is an intron?
A region within a gene but doesn’t remain in the final mRNA molecule.
They are NON-CODING sequences in DNA (junk DNA)
What is a locus?
The position of the gene on the DNA.
What is an allele?
A different version/form of the same gene.
What are the features of the genetic code?
> It is DEGENERATE.
> It is UNIVERSAL.
> It is NON-OVERLAPPING.
What is a triplet of bases known as?
A codon.
What does it mean by the ‘code is degenerate’, and what are the advantages?
Means most amino acids are coded for by MORE THAN 1 triplet of bases (codon).
+ If there’s a point mutation (change in 1 base), then potentially the same amino acid may be produced - this is called a silent mutation.
Bc diff triplets may sometimes produce the same amino acid so the protein doesn’t change.
What does it mean by the ‘code is universal’, and what are the advantages?
The SAME triplet (codon) will code for the SAME amino acid in EVERY living organism.
+ This made genetic engineering possible
(e.g. inserting human insulin gene into bacteria)
What does it mean by the ‘code is non-overlapping’, and what are the advantages?
Each base is only part of 1 triplet so each triplet is separate with no overlap.
+ A point mutation would only affect 1 TRIPLET and so only 1 amino acid is affected, MINIMISING the impact.
What do non-coding regions of DNA (introns) do?
> Some regulate gene expression
Some are relics from viral infections in our evolutionary history.
Some are random long repeating sequences BETWEEN genes.
The diagram shows a short sequence of DNA bases.
TTT GTA TAC TAG TCT ACT TCG TTA ATA
What is the maximum number of amino acids for which this base sequence could code? [1 mark]
9
There are 9 triplets, and each triplet codes for 1 amino acid.
The number of amino acids coded for could be fewer than your answer.
Give one reason why. [1 mark]
They could be introns/non-coding DNA. (1)
Explain how a change in the DNA base sequence for a protein may result in a change in the structure of the protein. [3 marks]
Change in amino acids / primary structure. (1)
Change in hydrogen/ionic/disulfide bonds. (1)
Alters tertiary structure. (1)
A gene codes for the α-polypeptide chain. There are 423 bases in this gene that code for amino acids. How many amino acids are there in the α-polypeptide chain? [1 mark]
423 / 3 = 141
141 amino acids.
The total number of bases in the DNA of the α-polypeptide gene is more than 423.
Give 2 reasons why there are more than 423 bases. [2 marks]
> Non-coding DNA repeats. (1)
> Addition of base by mutation. (1)
DNA in eukaryotes are…
Long and linear
DNA in prokaryotes are…
Short and circular
What’s the difference between the DNA in eukaryotes and prokaryotes?
Eukaryotes =
> Long and linear
Prokaryotes =
> Short and circular
> Contains plasmids
