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Biology · OCR Paper 1

What Happens in Cells

How DNA is built and how it carries a code for making proteins, and how enzymes speed up the reactions in cells. It covers DNA as a polymer, nucleotides and complementary base pairs, protein synthesis, the lock and key model, and the effect of temperature and pH on enzymes. Matches OCR GCSE Biology A (Gateway Science) B1.2 (what happens in cells). The nucleotide and protein synthesis lesson is for separate Biology only, and its protein synthesis section is for the Higher tier only. The other lessons are for both Combined Science and separate Biology.

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Lessons

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Key terms in this chapter

All 38, gathered from every lesson.

DNA
The molecule that stores the genetic information of a cell.
Polymer
A large molecule made of many smaller units joined together.
Double helix
The twisted ladder shape of DNA: two strands wound round each other.
Gene
A section of DNA that codes for a particular protein.
Chromosome
A long, coiled molecule of DNA that carries many genes.
Genome
All of the genetic material of an organism.
Plasmid
A small ring of DNA found in bacterial cells.
Nucleotide
One of the units that are joined to make a strand of DNA.
Nucleotide
A unit of DNA made of a phosphate group, a sugar and one base.
Base
One of the four chemicals A, T, G and C in DNA.
Complementary base pairing
The rule that A pairs with T and G pairs with C.
mRNA
A copy of a gene, made in the nucleus, that carries the code to the ribosome (Higher tier).
Transcription
Making a copy of a gene as mRNA (Higher tier).
Translation
Reading the mRNA at the ribosome to join amino acids in order (Higher tier).
tRNA
The molecule that carries an amino acid to the ribosome (Higher tier).
Triplet
A group of three bases that codes for one amino acid (Higher tier).
Enzyme
A biological catalyst, made of protein, that speeds up a reaction in a living thing.
Catalyst
A substance that speeds up a chemical reaction and is not used up.
Substrate
The substance that an enzyme acts on.
Product
A substance that is made in a reaction.
Active site
The region of an enzyme, with a particular shape, into which the substrate fits.
Enzyme-substrate complex
The enzyme and its substrate joined together while the reaction takes place.
Lock and key model
A model in which the substrate fits the active site as a key fits a lock.
Specific
Working on one particular substrate only.
Denatured
Having lost its normal shape, so that the active site no longer fits the substrate.
Optimum
The temperature or pH at which an enzyme works fastest.
Rate of reaction
A measure of how fast a reaction goes.
Continuous sampling
Taking a small sample at regular intervals during a reaction and testing each one.
Buffer solution
A solution that keeps the pH constant at a particular value.
Spotting tile
A tile with small wells, used to test many small drops one after the other.
Independent variable
The variable that you change in an investigation.
Dependent variable
The variable that you measure in an investigation.
Control variable
A variable that you keep the same, so that it does not affect the results.
Water bath
A container of water at a steady temperature, used to keep the temperature of the tubes constant.
Optimum pH
The pH at which an enzyme works fastest.
Rate of reaction
A measure of how fast a reaction goes, worked out here as 1000 ÷ time.
Anomalous result
A result that does not fit the pattern, and is probably due to an error.
Reliable
Giving similar results when the investigation is repeated.