Describe DNA in the nucleus of a eukaryotic cell.

Very long, linear and associated with histones.

What is a chromosome in a eukaryote?

A DNA molecule together with its associated proteins (histones).

How does the DNA in mitochondria compare with prokaryotic DNA?

It is similar: short, circular and not associated with protein.

A base sequence of DNA that codes for the amino acid sequence of a polypeptide or a functional RNA.

The fixed position of a gene on a particular DNA molecule.

Sequences within a gene that code for amino acids.

Non-coding sequences within a gene that separate exons.

Give an example of non-coding DNA between genes.

Multiple repeats of base sequences.

Does all nuclear DNA code for polypeptides?

No; much is non-coding, such as introns and multiple repeats.

DNA, genes and chromosomesAQA A-Level Biology: Flashcards

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Describe DNA in a prokaryotic cell.

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Describe DNA in a prokaryotic cell.: Short, circular and not associated with proteins.
Describe DNA in the nucleus of a eukaryotic cell.: Very long, linear and associated with histones.
What is a chromosome in a eukaryote?: A DNA molecule together with its associated proteins (histones).
Which proteins is nuclear DNA associated with?: Histones.
Which two organelles contain DNA?: Mitochondria and chloroplasts.
How does the DNA in mitochondria compare with prokaryotic DNA?: It is similar: short, circular and not associated with protein.
Define a gene.: A base sequence of DNA that codes for the amino acid sequence of a polypeptide or a functional RNA.
Give two examples of functional RNA.: Ribosomal RNA (rRNA) and tRNA.
What is a locus?: The fixed position of a gene on a particular DNA molecule.
What are exons?: Sequences within a gene that code for amino acids.
What are introns?: Non-coding sequences within a gene that separate exons.
Give an example of non-coding DNA between genes.: Multiple repeats of base sequences.
Does all nuclear DNA code for polypeptides?: No; much is non-coding, such as introns and multiple repeats.

Exam questions on DNA, genes and chromosomes

A student compares the DNA in a bacterium, Escherichia coli, with the DNA in a human liver cell.
Describe how the DNA in the nucleus of the liver cell differs from the DNA in the bacterium.2 marks
Human cells contain a gene for the polypeptide β-globin, found on chromosome 11. They also contain genes that are transcribed to make ribosomal RNA (rRNA) and transfer RNA (tRNA). Each of these genes is always found at the same position on its chromosome.
The rRNA genes are transcribed but their products are never translated into polypeptides. Explain why these sequences are still called genes.2 marks
A human nuclear gene has three exons and two introns arranged alternately (exon, intron, exon, intron, exon). The exons contain 150, 210 and 90 bases, and the introns contain 400 and 1000 bases. Human cells also contain mitochondria, which have their own DNA.
Calculate the percentage of the bases in this gene that are in exons, and state why only the exons affect the amino acid sequence of the polypeptide.3 marks

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Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).