3.4.1 DNA, Genes and Chromosomes Flashcards Preview

Grice/Hall AQA A-Level Biology Revision Year 13 > 3.4.1 DNA, Genes and Chromosomes > Flashcards

Flashcards in 3.4.1 DNA, Genes and Chromosomes Deck (14)
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1
Q

What is a gene?

A

A section of DNA that contains the coded information for making polypeptides and functional RNA

2
Q

Why is it necessary for three bases to code for one amino acid?

A

Only 20 different amino acids regularly occur in proteins
Each amino acid must have its own code of bases on the DNA
There are only four different bases that are present in DNA
If each base coded for a different amino acid only four different amino acids could be coded for
Using a pair of bases, 16 different codes are possible which is still inadequate
Three bases produce 64 different codes which are more than enough to create 20 amino acids

3
Q

What is a DNA triplet?

A

Each amino acid is a triplet, consisting of 3 bases
There are 64 possible triplets so some amino acids are coded for by more than one triplet
A triplet is always read in one particular direction along the DNA strand
Three triplets don’t always code for an amino acid- some are stop codes which mark the end of a polypeptide chain

4
Q

What is degenerate code?

A

Because most amino acids are coded by more than one triplet

5
Q

How is the DNA code universal?

A

The code is universal with a few minor exceptions as each triplet codes for the same amino acid in all organisms

6
Q

Why is DNA non-overlapping?

A

Because each base is read once

7
Q

What are introns and exons?

A

Exons are coding sequences which code for amino acids

Introns are non-coding sequences that separate exons

8
Q

What is a chromosome?

A

DNA molecules which form a line (are linear) and occur in association with proteins called histones
Found in eukaryotic cells

9
Q

What are homologeous chromosomes?

A

Chromosomes consisting of two chromatids with identical DNA

10
Q

What is the structure of a chromosome?

A

DNA is in a double helix
Helix is wound around histones to fix it in position
DNA-histone complex is then coiled
Coil is in turn looped and further coiled before being packed into the chromosome

11
Q

What is an allele?

A

An allele is one of a number of alternative forms of a gene

12
Q

What causes mutation?

A

Any changes in the base sequence of a gene produces a new allele of that gene (mutation)

13
Q

What is a gene locus?

A

A fixed position on a chromosome

14
Q

How are introns/exons different in eukaryotic and prokaryotic cells?

A

Introns are more likely to be in eukaryotic cells

Prokaryotes do not have noncoding DNA so splicing does not occur

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