B1.2

Question 1

Describe the structure of DNA

Answer 1

• DNA is a polymer that is made up of two strands, forming a double helix

Question 2

What is DNA made from?

Answer 2

• 4 different nucleotides
• adenine (A) & thymine (T)
• Cytosine (C) Guanine (G)

Question 3

Recall a simple description of protein synthesis transcription

Answer 3

1. The two strands of the DNA are unzipped by breaking of the weak Hydrogen bonds between base pairs
2. The enzyme RNA attaches to the DNA and moves along it
3. RNA nucleotides form hydrogen bonds with the exposed DNA strand nucleotides by complementary base pairing to form a strand of mRNA A&U C&G
4. Note RNA has base U instead of T which pairs up with A in DNA 🧬 and a complimentary copy is formed

Question 4

recall a simple description of protein synthesis transcription

Answer 4

1. mRNA strand travels through the cytoplasm and attaches to the ribosome
2. every three mRNA bases (codon)the ribosome lines up one complementary molecule of tRNA
3. tRNA molecules transport specific amino acids to the ribosome which they leave behind shortly after lining up opposite the DNA.
4. Because there are three mRNA bases for each tRNA molecule, we call this the triplet code.
5. A chain of several hundred amino acids in the correct order according to the original DNA is then made. This is called a polypeptide
6. After translation, the polypeptide is finally folded into the correct complex shape and becomes a protein

Question 5

explain the mechanism of enzyme action

Answer 5

• Enzymes have an active site that’s specifically shaped for the shape of a specific substrate
• Substrate and enzyme’s active site combine to form a enzyme-substrate complex by ether building or braking down substrate
• Products separate from the the active site of enzyme

Question 6

explain simply how the structure of DNA affects the proteins made in protein synthesis, to include the triplet code

Answer 6

1. each different protein has its own particular number and order of amino acids
2. this gives each proteins a different shape which ,means it can have a different function
3. order of bases in a gene decides order of amino acids
4. each amino acid is coded for a sequence of three bases called a triplet code
5. the amino acids are joined together to make proteins following the order of bases in a gene

Question 7

describe experiments that can be used to measure enzymatic reactions potato catalase experiment (PAG)

Answer 7

• the enzyme catalase catalyzes the breakdown of hydrogen peroxide into water and oxygen
• you can collect the oxygen and measure how much is produced in a set time

1. use a pipette to add a set amount to hydrogen peroxide to a boiling tube.
2. put the boiling tube in water bath at 10° C degrees
3. set up the rest of the apparatus as show in image
4. add 1cm³ of potato to the hydrogen peroxide and quickly attach bung
5. record how much oxygen is produced in the first minute. repeat three times to find the mean.
6. repeat at 20°C 30°C and 40°C
7. Control any variables: Potatoe used size of potatoes to keep it a fair test
8. Calculate the mean rate of reaction at each temperature by dividing the mean volume of oxygen produced by the time taken
9. The units will be cm³/ second

Question 8

Describe experiments that can be used to investigate enzymatic reactions (PAG) amylase

Answer 8

1. The enzyme amylase catalyzes the breakdown of starch to maltose
2. starch can be detected using iodine solution - if starch is present the iodine solution will change from browny orange to blue black
3. Set up the water bath, boiling tube, dropping pipette, spotting tile
4. Put a drop of iodine solution into each well on the spotting tile
5. Every ten seconds, drop a sample of the mixture into a well using a pipette
6. When the iodine solution remains browny orange record the total time taken
7. repeat with the water bath at different to temperatures to see how it effects the time taken for the starch to be broken down
8. Remember to control all of the variables each time

Question 9

How can you improve the accuracy of the amylase experiment

Answer 9

• Use a colourimetre
• a colourimetre is a piece of electronic equipment that measures the strength of a coloured solutions so measurements are just based on someone’s judgement

Question 10

Explain the mechanism of enzymes action

Answer 10

• Enzymes are proteins that act as biological catalysts - this means they speed up reactions without being used up.
• An enzyme works on the substrate, forming products.
• An enzyme’s active site and its substrate are complementary in shape.
• An enzyme will only work on one substrate - it is substrate-specific.
• Enzymes and substrates collide to form enzyme-substrate complexes.
• The substrates are broken down (or in some cases built up).
• The products are released.
• The enzyme is free to act again.
  This theory is known as the ‘lock and key model’.
• It explains why each enzyme will only work on one substrate.

Question 11

Explain the lock and key theory

Answer 11

1. Substrate collides with active site of enzyme and becomes attached
2. Active site has a complementary shape to the substrate
3. Enzyme catalyses breakdown of substrate
4. Products released from active site
5. Enzyme molecule is unchanged and can be reused