Topic 6 - Inheritence, variation and evolution - Protein synthesis

Question 1

What are the two stages of protein synthesis?

Answer 1

Transcription and translation

Question 2

What is a gene?

Answer 2

A gene is a section of DNA with a particular sequence of bases that codes for a particular sequence of amino acids

Question 3

What is DNA made of?

Answer 3

DNA is made by linking many nucleotides together in a long chain

Question 4

What is each nucleotide made up of?

Answer 4

1. Phosphate group
2. Pentose sugar
3. Nitrogenous base

Question 5

How does the structure of DNA and RNA nucleotides alter?

Answer 5

1. They both have the same phosphate group
2. In all DNA nucleotides the pentose sugar is deoxyribose, but in all RNA nucleotides the pentose sugar is ribose
3. In DNA nucleotides the nitrogenous bases alter, in RNA they also alter but Uracil (U) replaces Thymine (T)

Question 6

What are the four nitrogenous bases?

Answer 6

1. Adenine (A)
2. Thymine (T)
3. Cytosine (C)
4. Guanine (G)

Question 7

What are the complimentary base pairings in DNA?

Answer 7

1. Adenine pairs with Thymine, so A pairs with T
2. Cytosine pairs with Guanine, so C pairs with G

Question 8

What are the complimentary base pairings in RNA?

Answer 8

1. Adenine pairs with Uracil, so A pairs with U
2. Cytosine pairs with Guanine, so C pairs with G

Question 9

What is the sequence of three bases?

Answer 9

A sequence of three bases is the code for a single specific amino acid

Question 10

What is the scientifc term for three bases?

Answer 10

Codon

Question 11

What do the order of bases control in a nucleotide?

Answer 11

1. The order and different types of amino acids that are eventually joined together in a polypeptide chain
2. These polypeptide chains (the amino acid sequences) then form a particular type of protein
3. It is the order of bases in the DNA that eventually determines which proteins are produced

Question 12

Enzymes function?

Answer 12

Act as a biological catalyst to speed up chemical reactions in the body

Question 13

Hormones function?

Answer 13

1. Carry messages around the body
2. E.g. insulin is a hormone released into the blood by the pancreas to regulate the blood sugar level

Question 14

Structural proteins function?

Answer 14

Proteins that provide structure and are physically strong

Question 15

What is mRNA?

Answer 15

1. Messenger RNA
2. Is a copy of a single gene

Question 16

Difference between mRNA and DNA?

Answer 16

1. mRNA is much shorter than DNA because it is only a single gene long
2. It is only a single strand rather than a double strand like DNA
3. Instead of Thymine it contains Uracil

Question 17

Why do we need mRNA?

Answer 17

1. Ribosomes have to read the sequence of bases to make a protein, and genes contain the sequences of bases needed to be read by ribosomes to make proteins
2. Ribosomes exist outside the nucleus
3. Genes are within the DNA in the nucleus, and DNA cannot leave the nucleus as it is too big
4. To use a gene, it has to be copied into mRNA so the instructions can be used to make a protein

Question 18

How does transcription work?

Answer 18

1. RNA polymerase enzyme binds to the start of the gene
2. The two strands of DNA split apart, so their bases are exposed
3. The RNA polymerase moves along the DNA, reading their bases one by one so that it can make a corresponding mRNA strand
4. As the RNA polymerase moves up the DNA, the DNA strand closes behind it, so only a small section of the gene is exposed at one time
5. When the mRNA strand is complete, the RNA molymerase detaches from the DNA, and the DNA strand completely closes
6. The mRNA can then leave the nucleus and go to a ribosomse

Question 19

How does translation work?

Answer 19

1. Each codon codes for a specfic amino acid
2. The mRNA strand and the ribosome bind together
3. The amino acids are brought to the ribosome by tRNA (transfer RNA)
4. tRNA have the amino acid at the top and the anti-codon at the bottom. The anticodon is a set of three bases that is complementary to a specific codon on the mRNA
5. The tRNAs bring the correct amino acid to the ribosome in the correct order so they can be joined together
6. When the ribosome reaches the end of the mRNA, a complete chain of amino acids is formed
7. The amino acid chain detaches from the ribosome and folds up to make a protein

Question 20

What is a mutation?

Answer 20

A random change in an organism’s DNA base sequence

Question 21

Wen do mutations occur?

Answer 21

1. Mutations occur spontaneously in our cells e.g. when a chromosome isnt replicated properly
2. Carcinogens and radiation increase the risk of mutations

Question 22

How to code for a protein?

Answer 22

1. Our cells read the sequence as a set of codons - each codon codes for 1 of 20 amino acids
2. Take the amino acids that each codon forms
3. Combine the amino acids in the same order as the codons
4. The long chain of amino acids folds up to become a protein

Question 23

How are mutations bad?

Answer 23

1. Mutations change the suquence of the DNA bases in a gene, which produces a genetic variant
2. As the sequence of DNA bases codes for the sequence of amino acids that make up a protein, mutations to a gene sometimes lead to changes in the protein that it codes for
3. This could change the protein so it has a different active site and therefore the enzyme no longer fits the substrate

Question 24

Why do some mutations not matter?

Answer 24

1. Most mutations do not have significant effects as they mainly occur in non-coding DNA, which does not code for a protein
2. However, this can sometimes sometimes alter how genes are expressed

Question 25

What are the three types of mutation

Answer 25

1. Insertions 2. Deletions 3. Substitutions

Question 26

What are deletions?

Answer 26

1. Deletions are when a random base is deleted from the DNA base sequence 2. Like insertions, they change the way that the base sequence is read and have knock on effects

Question 27

What are substitutions?

Answer 27

Substitution mutations are when a random base in the DNA base sequence is changed to a different base

Question 28

What are insertions?

Answer 28

1. Insertions are when a new base is inserted into the DNA base sequence where it shouldn't be 2. An insertion changes the way the groups of three bases are read, which can change the amino acids they code for 3. Insertions can change more than one amino acids as they have a knock on effect on the bases further on in the sequence