A2 OCR Biology Key Terms and Definitions Cellular Control

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Nucleotides
A molecule consisting of a five-carbon sugar, a phosphate group and a nitrogenous base.
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Adenine
One of the four nitrogenous bases found in DNA and RNA.
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Guanine
One of the four nitrogenous bases found in DNA and RNA.
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Cytosine
One of the four nitrogenous bases found in DNA and RNA.
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Thymine
One of the four nitrogenous bases found in DNA (but not RNA).
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Complementary Base Pairing
The pattern of pairing between the nitrogenous bases in a polynucleotide; in DNA, A pairs with T and C with G.
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Genetic Code
The three-letter code by which information is contained in a DNA molecule; a group of three bases specifies a particular amino acid to be added to a growing polypeptide chain.
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Gene
A sequence of DNA nucleotides that codes for a polypeptide.
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Reference Strand
The strand of a DNA molecule against which mRNA is built up during transcription.
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Triplet
A group of three bases in a DNA molecule, coding for one amino acid.
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Messenger RNA (mRNA)
RNA that is made in the nucleus, complementary to the DNA of a gene, before travelling to a ribosome and taking part in protein synthesis.
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Transcription
Producing an mRNA molecule with a complementary base sequence to one strand of a length of DNA.
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Translation
The synthesis of proteins on a ribosome; the sequence of amino acids is determined by the sequence of bases in the mRNA.
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DNA Helicase
An enzyme that unwinds and separates the two strands of a DNA molecule.
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Uracil
One of the four nitrogenous bases found in RNA (but not DNA).
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RNA Polymerase
An enzyme that links together RNA nucleotides during transcription.
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Codon
A sequence of three bases in mRNA that codes for one amino acid.
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Transfer RNA (tRNA)
A type of RNA found in the cytoplasm, made of a single strand looped back on itself; each tRNA molecule has a particular anticodon that pairs with a codon on mRNA, and also determines the type of amino acid with which the tRNA will bind.
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Anticodon
A sequence of three bases on a tRNA molecule that determines the specific amino acid it can pick up, and the mRNA codon with which it can bind.
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tRNA Transferase
An enzyme that loads a specific amino acid onto a specific tRNA molecule.
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Mutation
An unpredictable change in the structure of DNA, or in the structure and number of chromosomes.
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Substitution
The replacement of one base pair from a DNA molecule with another.
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Degenerate
A term used to describe the genetic code, in which more than one triplet of bases codes for the same amino acid.
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Deletion
The loss of one base pair from a DNA molecule.
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Frame Shift
The result of adding or removing one base pair from a DNA molecule, so that the way in which every subsequent triplet is read is altered.
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Insertion
The addition of one base pair to a DNA molecule.
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Sickle Cell Anaemia
A genetic disease caused by a faulty allele of the gene that codes for the β chains in haemoglobin.
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β Galactoside Permease (Lactose Permease)
An enzyme produced by Escherichia coli which allows lactose to enter the cell; also known as lactose permease.
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β Galactosidase (Lactase)
An enzyme produced by Escherichia coli, which catalyses the hydrolysis of lactose to glucose and galactose; also known as lactase.
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Lac Operon
The length of DNA in Escherichia coli which controls the production of lactose permease and β galactosidase.
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Structural Genes
The part of an operon that codes for the amino acid sequence in a protein.
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Promoter
A length of DNA that is needed for a gene to be transcribed; in a prokaryotic cell, part of an operon to which RNA polymerase binds in order to initiate transcription of the gene.
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Operator
In a prokaryotic cell. Part of an operon to which another molecule can bind, covering the promoter and preventing transcription.
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Repressor Protein
A protein that can bind to the operator in an operon, blocking the promoter and preventing transcription.
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Homeobox Genes
A gene whose activity switches a whole set of other genes on or off, affecting an organism’s body plan; all animals have very similar homeobox genes, as do all plants.
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Body Plan
The overall design of an organism’s body.
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Homologous
Having similar base sequences (in genes).
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Transcription Factors
A substance that can bind with a particular region of DNA and either initiate or prevent transcription.
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Metamorphosis
A major change in an organism’s body plan as it moves from one stage in its life cycle to another – for example, a tadpole to a frog, or a caterpillar to a butterfly.
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Programmed Cell Death
Controlled process by which cells die, which it important in the development of an embryo to an adult; also called apoptosis.
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Apoptosis
Controlled process by which cells die, which is important in the development of an embryo to an adult; also called programmed cell death.
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Card 2

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One of the four nitrogenous bases found in DNA and RNA.

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Adenine

Card 3

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One of the four nitrogenous bases found in DNA and RNA.

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Preview of the back of card 3

Card 4

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One of the four nitrogenous bases found in DNA and RNA.

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Preview of the back of card 4

Card 5

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One of the four nitrogenous bases found in DNA (but not RNA).

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