What Happens in Cells (& What do Cells Need?) (OCR GCSE Combined Science A (Gateway): Biology): Flashcards
Exam code: J250
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- FrontDNA Structure
Define DNA.
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Define DNA.
Deoxyribonucleic acid — the molecule that carries the genetic instructions for the growth and development of an organism.
Define polymer.
A large molecule made from many repeating subunits, called monomers, joined together.
What are the monomers that make up a molecule of DNA?
Nucleotides.
Why is DNA described as a polymer?
It is built from many repeating nucleotide monomers joined into a long chain.
The monomers of DNA are joined together to form a single long ＿＿＿＿＿＿＿＿.
The monomers of DNA are joined together to form a single long strand.
Define double helix.
The shape of a DNA molecule — two strands coiled around each other in a spiral, like a twisted ladder.
How many strands make up a molecule of DNA?
Two, coiled around one another to form a double helix.
Two long chains of nucleotides coil around each other to form a ＿＿＿＿＿＿＿＿.
Two long chains of nucleotides coil around each other to form a double helix.
Where is DNA found in a eukaryotic cell?
In the nucleus, where it is contained in structures called chromosomes.
What is the relationship between DNA and a chromosome?
A chromosome is a long molecule of DNA. DNA is packaged into chromosomes so it can be stored in the nucleus.
What does DNA carry the instructions to make?
Proteins — the molecules an organism needs for life.
True or False?
A DNA molecule is a single straight chain of nucleotides.
False.
DNA has two strands, and they are coiled around each other into a double helix.
True or False?
Every person's DNA is unique, except for identical twins.
True.
Identical twins develop from the same fertilised egg, so they carry the same DNA.
Define enzyme.
A biological catalyst that speeds up the rate of a chemical reaction without being changed or used up.
Define metabolism.
The sum of all the chemical reactions happening in a cell or organism.
What is the role of enzymes in metabolism?
They control the reactions of metabolism, allowing them to happen fast enough to sustain life without needing high temperatures.
Define active site.
The specially shaped region of an enzyme that the substrate binds to, where the reaction takes place.
Define substrate.
The molecule that an enzyme acts on and changes during a reaction.
What is meant by enzyme specificity?
Each enzyme works on only one type of substrate.
This is because the shape of the active site is complementary to the shape of its substrate.
Explain the lock and key hypothesis.
The enzyme is the lock and the substrate is the key.
Only a substrate with the correct shape fits into the active site, so only that reaction is catalysed.
Why does raising the temperature at first increase the rate of reaction?
The enzyme and substrate molecules gain kinetic energy and move faster, so they collide more often.
What happens to an enzyme above its optimum temperature?
The bonds holding it together break and the active site loses its shape.
The enzyme is denatured, the substrate no longer fits, and the reaction stops.
The temperature at which an enzyme works fastest is called its ＿＿＿＿＿＿＿＿ temperature.
The temperature at which an enzyme works fastest is called its optimum temperature.
How does a pH far from the optimum affect an enzyme?
The bonds holding the protein in shape are disrupted, changing the shape of the active site.
The substrate no longer fits, so the rate of reaction falls and the enzyme is eventually denatured.
How does increasing substrate concentration affect the rate of reaction?
The rate increases, because enzymes and substrate are more likely to collide.
Once all the active sites are full the rate levels off, as extra substrate has nowhere to bind.
How does increasing enzyme concentration affect the rate of reaction?
The rate increases, because there are more active sites available for the substrate to bind to.
How can iodine solution be used to follow the breakdown of starch?
Iodine turns blue-black when starch is present.
When the amylase has broken all the starch down, the iodine stays orange-brown.
Write the equation used to calculate the rate of an enzyme reaction.
Rate = change ÷ time
'Change' is the amount of substrate used up or product formed.
45 cm³ of oxygen is released in 5 minutes. Calculate the rate.
Rate = amount of product formed ÷ time
45 ÷ 5 = 9 cm³/min
True or False?
An enzyme is used up in the reaction it catalyses.
False.
Enzymes are not changed or used up, so the same enzyme molecule can be used again and again.
True or False?
A denatured enzyme can return to its original shape.
False.
Denaturing is irreversible — the active site does not go back to its original shape.
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