OCR GCE Biology (A) Module 2 - Nucleic Acids

The double helix is:

The shape of the DNA molecule, due to coiling of two sugar-phosphate backbone strands into a right-handed spiral

A monomer is:

A molecule that, when repeated, makes up a polymer. E.g. nucleotides are repeated to form RNA or DNA

A nucleotide is:

A molecule consisting of a five-carbon sugar, a phosphate group and a nitrogenous base

A polynucleotide is:

A large molecule containing many nucleotide monomers
(e.g. RNA or DNA are both polynucleotides)

The pentose sugar in an RNA nucleotide is:

Ribose

The pentose sugar in a DNA nucleotide is:

Deoxyribose

A nucleotide is made from:

A pentose sugar, nitrogenous base, and a phosphate group

The purines are:

Adenine and guanine

The pyrimidines are:

Thymine and cytosine

The type of bond that joins the two DNA strands together are:

Hydrogen bonds

The number of hydrogen bonds that link adenine with thymine is:

Two

The number of hydrogen bonds that link guanine with cytosine is:

Three

The enzyme that catalyses formation of DNA from activated deoxyribose nucleotides, using single-stranded DNA as a template is:

DNA polymerase

The enzyme that catalyses the breaking of hydrogen bonds between the nitrogenous pairs of bases in a DNA molecule is:

Helicase

The term used to describe how DNA replicates, resulting in two new molecules, each of which contains one old strand and one new strand is:

Semi-conservative replication

All of the DNA within a cell is known as the:

Genome

The direction that free nucleotides are added by DNA polymerase is in the:

5' to 3' direction

During semi-conservative replication of DNA, the leading strand is synthesised ................., whereas the lagging strand is in fragments

Continuously

The way prokaryotic DNA replicates is also semi-conservatively. Other circular DNA that replicates like this is found in:

Chloroplasts and mitochondria

Meselson and Stahl's experiments that proved DNA replicated semi-conservatively, used:

Heavy nitrogen (15N)

A mutation is:

A change to the genetic information of an organism

An allele is:

A different version of a gene
(e.g. T or t)

An example of an advantageous mutation is:

An animal's white fur coat in winter when snow is on the ground

An example of a neutral mutation
(i.e. neither advantageous or disadvantageous) is:

The ability of humans to roll their tongues

A gene is:

A length of DNA that codes for a polypeptide, or for a length of RNA that is involved in regulating gene expression

A polypeptide is:

A polymer made of many amino acid units joined together by peptide bonds
(e.g. insulin is made of 51 amino acids)

A protein is:

A large polypeptide of 100 or more amino acids.

Transcription is:

The process of making messenger RNA (mRNA) from a DNA template

Translation is:

The formation of a protein, at ribosomes, by assembling amino acids into a particular sequence according to the coded instructions carried from DNA to the ribosome by mRNA

The structure of RNA is different from DNA because:

The nucleotide sugar is ribose, uracil replaces thymine, it is single-stranded, is shorter, and there are 3 forms

Where, precisely, are proteins synthesised in the cell?

At ribosomes in the cytoplasm

The genetic code is termed 'universal' because:

Almost all organisms use the same triplet of DNA bases that codes for the same amino acid

The genetic code is 'degenerate' because:

For all amino acids (except methionine and tryptophan) there is more than one base triplet code

The genetic code is 'non-overlapping' because:

It is read starting from a fixed point in groups of 3 bases. If a base is added or deleted, it causes a frame shift and every amino acid
upstream from it is changed

A codon is:

A sequence of three bases of mRNA that control the insertion of one amino acid
into a polypeptide

An anticodon is:

A sequence of three bases of tRNA that is complementary
to a specific codon