8.1: Genes and the triplet code

Question 1

Codons

Answer 1

Codons are triplets of base pairs

Question 2

Some of the roles of proteins in our bodies

Answer 2

Some of the roles of proteins in our bodies are as:

1. Enzymes
2. Channel proteins
3. Carrier proteins

Question 3

The genetic code is a triplet code.

What does this mean?

Answer 3

This means that 3 bases code for one amino acid

Question 4

A gene is a section of DNA that contains the coded information for making polypeptides and functional RNA.
The coded information is in the form of a specific sequence of bases along the DNA molecule.
What do polypeptides make up?

Answer 4

Polypeptides make up proteins

Question 5

A gene is a section of DNA that contains the coded information for making polypeptides and functional RNA.
The coded information is in the form of a specific sequence of bases along the DNA molecule.
Polypeptides make up proteins and so what do genes determine?

Answer 5

Polypeptides make up proteins and so genes determine the proteins of an organism

Question 6

A gene is a section of DNA that contains the coded information for making polypeptides and functional RNA.
The coded information is in the form of a specific sequence of bases along the DNA molecule.
Polypeptides make up proteins and so genes determine the proteins of an organism.
If there is a mutation, what could happen?

Answer 6

If there is a mutation, that protein could become non-functional

Question 7

A gene is a section of DNA that contains the coded information for making polypeptides and functional RNA.
The coded information is in the form of a specific sequence of bases along the DNA molecule.
Polypeptides make up proteins and so genes determine the proteins of an organism.
If there is a mutation, that protein could become non-functional.
Enzymes are proteins.
As enzymes control chemical reactions, what are they responsible for?

Answer 7

As enzymes control chemical reactions, they are responsible for an organism’s:

1. Development
2. Activities

Question 8

A gene is a section of DNA that contains the coded information for making polypeptides and functional RNA.
The coded information is in the form of a specific sequence of bases along the DNA molecule.
Polypeptides make up proteins and so genes determine the proteins of an organism.
If there is a mutation, that protein could become non-functional.
Enzymes are proteins.
As enzymes control chemical reactions, they are responsible for an organism’s development and activities.
Genes, along with environmental factors, determine the what of all organisms?

Answer 8

Genes, along with environmental factors, determine:
1. The nature
2. The development
of all organisms

Question 9

A gene is a section of DNA that contains the coded information for making polypeptides and functional RNA.
The coded information is in the form of a specific sequence of bases along the DNA molecule.
Polypeptides make up proteins and so genes determine the proteins of an organism.
If there is a mutation, that protein could become non-functional.
Enzymes are proteins.
As enzymes control chemical reactions, they are responsible for an organism’s development and activities.
Genes, along with environmental factors, determine the nature and the development of all organisms.
A gene is a section of DNA at a particular position, called what, on a DNA molecule?

Answer 9

A gene is a section of DNA at a particular position, called a locus, on a DNA molecule

Question 10

Gene

Answer 10

A gene is a base sequence of DNA that codes for:
1. The amino acid sequence of a polypeptide
Or,
2. A functional RNA

Question 11

A gene is a base sequence of DNA that codes for the amino acid sequence of a polypeptide or a functional RNA, including what?

Answer 11

A gene is a base sequence of DNA that codes for:
1. The amino acid sequence of a polypeptide
Or,
2. A functional RNA, including ribosomal RNA and transfer RNA

Question 12

DNA codes for amino acids, but what is it made up of?

Answer 12

DNA:
1. Codes for amino acids
,but
2. It is made up of nucleotides

Question 13

What is the sequence of amino acids coded for by DNA?

Answer 13

The sequence of amino acids coded for by DNA is the primary structure of a protein

Question 14

The sequence of amino acids coded for by DNA is the primary structure of a protein.
It is the primary structure that gives rise to what?

Answer 14

It is the primary structure that gives rise to the tertiary structure

Question 15

The sequence of amino acids coded for by DNA is the primary structure of a protein.
It is the primary structure that gives rise to the tertiary structure and hence what?

Answer 15

It is the primary structure that gives rise to:

1. The tertiary structure
2. Hence the shape of the protein

Question 16

The sequence of amino acids coded for by DNA is the primary structure of a protein.
It is the primary structure that gives rise to the tertiary structure and hence the shape of the protein.
So what does DNA indirectly do?

Answer 16

So DNA indirectly codes for the shape of proteins

Question 17

The sequence of amino acids coded for by DNA is the primary structure of a protein.
It is the primary structure that gives rise to the tertiary structure and hence the shape of the protein.
So DNA indirectly codes for the shape of proteins, including what?

Answer 17

So DNA indirectly codes for the shape of proteins, including enzymes

Question 18

In trying to discover how DNA bases coded for amino acids, scientists suggested that there must be a minimum of 3 bases that coded for each amino acid.
Their reasoning was as follows:
1. Only how many different amino acids occur regularly in proteins?

Answer 18

Only 20 different amino acids occur regularly in proteins

Question 19

In trying to discover how DNA bases coded for amino acids, scientists suggested that there must be a minimum of 3 bases that coded for each amino acid.
Their reasoning was as follows:
1. Only 20 different amino acids occur regularly in proteins.
2. What must each amino acid have?

Answer 19

Each amino acid must have its own code of bases on the DNA

Question 20

In trying to discover how DNA bases coded for amino acids, scientists suggested that there must be a minimum of 3 bases that coded for each amino acid.
Their reasoning was as follows:
1. Only 20 different amino acids occur regularly in proteins.
2. Each amino acid must have its own code of bases on the DNA.
3. Only how many different bases (what) are present in DNA?

Answer 20

Only 4 different bases (adenine, guanine, cytosine and thymine) are present in DNA

Question 21

In trying to discover how DNA bases coded for amino acids, scientists suggested that there must be a minimum of 3 bases that coded for each amino acid.
Their reasoning was as follows:
1. Only 20 different amino acids occur regularly in proteins.
2. Each amino acid must have its own code of bases on the DNA.
3. Only 4 different bases (adenine, guanine, cytosine and thymine) are present in DNA.
4. If each base coded for a different amino acid, then what?

Answer 21

If each base coded for a different amino acid, then only 4 different amino acids could be coded for

Question 22

In trying to discover how DNA bases coded for amino acids, scientists suggested that there must be a minimum of 3 bases that coded for each amino acid.
Their reasoning was as follows:
1. Only 20 different amino acids occur regularly in proteins.
2. Each amino acid must have its own code of bases on the DNA.
3. Only 4 different bases (adenine, guanine, cytosine and thymine) are present in DNA.
4. If each base coded for a different amino acid, then only 4 different amino acids could be coded for.
5. Using a pair of bases, (4²) 16 different codes are possible, which is what?

Answer 22

Using a pair of bases, (4²) 16 different codes are possible, which is still inadequate

Question 23

In trying to discover how DNA bases coded for amino acids, scientists suggested that there must be a minimum of 3 bases that coded for each amino acid.
Their reasoning was as follows:
1. Only 20 different amino acids occur regularly in proteins.
2. Each amino acid must have its own code of bases on the DNA.
3. Only 4 different bases (adenine, guanine, cytosine and thymine) are present in DNA.
4. If each base coded for a different amino acid, then only 4 different amino acids could be coded for.
5. Using a pair of bases, (4²) 16 different codes are possible, which is still inadequate.
6. How many different codes do 3 bases produce?

Answer 23

3 bases produce (4³) 64 different codes

Question 24

In trying to discover how DNA bases coded for amino acids, scientists suggested that there must be a minimum of 3 bases that coded for each amino acid.
Their reasoning was as follows:
1. Only 20 different amino acids occur regularly in proteins.
2. Each amino acid must have its own code of bases on the DNA.
3. Only 4 different bases (adenine, guanine, cytosine and thymine) are present in DNA.
4. If each base coded for a different amino acid, then only 4 different amino acids could be coded for.
5. Using a pair of bases, (4²) 16 different codes are possible, which is still inadequate.
6. 3 bases produce (4³) 64 different codes, more than enough to do what?

Answer 24

3 bases produce (4³) 64 different codes, more than enough to satisfy the requirements of 20 amino acids

Question 25

In trying to discover how DNA bases coded for amino acids, scientists suggested that there must be a minimum of 3 bases that coded for each amino acid.
Their reasoning was as follows:
1. Only 20 different amino acids occur regularly in proteins.
2. Each amino acid must have its own code of bases on the DNA.
3. Only 4 different bases (adenine, guanine, cytosine and thymine) are present in DNA.
4. If each base coded for a different amino acid, then only 4 different amino acids could be coded for.
5. Using a pair of bases, (4²) 16 different codes are possible, which is still inadequate.
6. 3 bases produce (4³) 64 different codes, more than enough to satisfy the requirements of 20 amino acids.

As the code has 3 bases for each amino acid, what is each one called?

Answer 25

As the code has 3 bases for each amino acid, each one is called a triplet

Question 26

In trying to discover how DNA bases coded for amino acids, scientists suggested that there must be a minimum of 3 bases that coded for each amino acid.
Their reasoning was as follows:
1. Only 20 different amino acids occur regularly in proteins.
2. Each amino acid must have its own code of bases on the DNA.
3. Only 4 different bases (adenine, guanine, cytosine and thymine) are present in DNA.
4. If each base coded for a different amino acid, then only 4 different amino acids could be coded for.
5. Using a pair of bases, (4²) 16 different codes are possible, which is still inadequate.
6. 3 bases produce (4³) 64 different codes, more than enough to satisfy the requirements of 20 amino acids.

As the code has 3 bases for each amino acid, each one is called a triplet.
As there are 64 possible triplets and only 20 amino acids, what follows?

Answer 26

As there are 64 possible triplets and only 20 amino acids, it follows that some amino acids are coded for by more than one triplet

Question 27

Features of the genetic code:
Further experiments have revealed the following features of the genetic code:
1. A few amino acids are coded for by only what?

Answer 27

A few amino acids are coded for by only a single triplet

Question 28

Features of the genetic code:
Further experiments have revealed the following features of the genetic code:
1. A few amino acids are coded for by only a single triplet.
2. How are the remaining amino acids coded for?

Answer 28

The remaining amino acids are coded for by between:
1. 2
2. 6
triplets each

Question 29

Features of the genetic code:
Further experiments have revealed the following features of the genetic code:
1. A few amino acids are coded for by only a single triplet.
2. The remaining amino acids are coded for by between 2 and 6 triplets each.
3. Why is the genetic code known as a ‘degenerate code?’

Answer 29

The genetic code is known as a ‘degenerate code,’ because most amino acids are coded for by more than one triplet

Question 30

Features of the genetic code:
Further experiments have revealed the following features of the genetic code:
1. A few amino acids are coded for by only a single triplet.
2. The remaining amino acids are coded for by between 2 and 6 triplets each.
3. The genetic code is known as a ‘degenerate code,’ because most amino acids are coded for by more than one triplet.
4. How is a triplet always read?

Answer 30

A triplet is always read in one particular direction along the DNA strand

Question 31

Features of the genetic code:
Further experiments have revealed the following features of the genetic code:
1. A few amino acids are coded for by only a single triplet.
2. The remaining amino acids are coded for by between 2 and 6 triplets each.
3. The genetic code is known as a ‘degenerate code,’ because most amino acids are coded for by more than one triplet.
4. A triplet is always read in one particular direction along the DNA strand.
5. What is the start of a DNA sequence that codes for a polypeptide always?

Answer 31

The start of a DNA sequence that codes for a polypeptide is always the same triplet

Question 32

Features of the genetic code:
Further experiments have revealed the following features of the genetic code:
1. A few amino acids are coded for by only a single triplet.
2. The remaining amino acids are coded for by between 2 and 6 triplets each.
3. The genetic code is known as a ‘degenerate code,’ because most amino acids are coded for by more than one triplet.
4. A triplet is always read in one particular direction along the DNA strand.
5. The start of a DNA sequence that codes for a polypeptide is always the same triplet.
What does this code for?

Answer 32

This codes for the amino acid methionine

Question 33

Features of the genetic code:
Further experiments have revealed the following features of the genetic code:
1. A few amino acids are coded for by only a single triplet.
2. The remaining amino acids are coded for by between 2 and 6 triplets each.
3. The genetic code is known as a ‘degenerate code,’ because most amino acids are coded for by more than one triplet.
4. A triplet is always read in one particular direction along the DNA strand.
5. The start of a DNA sequence that codes for a polypeptide is always the same triplet.
This codes for the amino acid methionine.
If this first methionine molecule does not form part of the final polypeptide, what happens?

Answer 33

If this first methionine molecule does not form part of the final polypeptide, it is later removed

Question 34

Features of the genetic code:
Further experiments have revealed the following features of the genetic code:
1. A few amino acids are coded for by only a single triplet.
2. The remaining amino acids are coded for by between 2 and 6 triplets each.
3. The genetic code is known as a ‘degenerate code,’ because most amino acids are coded for by more than one triplet.
4. A triplet is always read in one particular direction along the DNA strand.
5. The start of a DNA sequence that codes for a polypeptide is always the same triplet.
This codes for the amino acid methionine.
If this first methionine molecule does not form part of the final polypeptide, it is later removed.
6. 3 triplets do not do what?

Answer 34

3 triplets do not code for any amino acid

Question 35

Features of the genetic code:
Further experiments have revealed the following features of the genetic code:
1. A few amino acids are coded for by only a single triplet.
2. The remaining amino acids are coded for by between 2 and 6 triplets each.
3. The genetic code is known as a ‘degenerate code,’ because most amino acids are coded for by more than one triplet.
4. A triplet is always read in one particular direction along the DNA strand.
5. The start of a DNA sequence that codes for a polypeptide is always the same triplet.
This codes for the amino acid methionine.
If this first methionine molecule does not form part of the final polypeptide, it is later removed.
6. 3 triplets do not code for any amino acid.
What are these called?

Answer 35

These are called ‘stop codes’

Question 36

Features of the genetic code:
Further experiments have revealed the following features of the genetic code:
1. A few amino acids are coded for by only a single triplet.
2. The remaining amino acids are coded for by between 2 and 6 triplets each.
3. The genetic code is known as a ‘degenerate code,’ because most amino acids are coded for by more than one triplet.
4. A triplet is always read in one particular direction along the DNA strand.
5. The start of a DNA sequence that codes for a polypeptide is always the same triplet.
This codes for the amino acid methionine.
If this first methionine molecule does not form part of the final polypeptide, it is later removed.
6. 3 triplets do not code for any amino acid.
These are called ‘stop codes’ and what do they do?

Answer 36

These are called ‘stop codes’ and they mark the end of a polypeptide chain

Question 37

Features of the genetic code:
Further experiments have revealed the following features of the genetic code:
1. A few amino acids are coded for by only a single triplet.
2. The remaining amino acids are coded for by between 2 and 6 triplets each.
3. The genetic code is known as a ‘degenerate code,’ because most amino acids are coded for by more than one triplet.
4. A triplet is always read in one particular direction along the DNA strand.
5. The start of a DNA sequence that codes for a polypeptide is always the same triplet.
This codes for the amino acid methionine.
If this first methionine molecule does not form part of the final polypeptide, it is later removed.
6. 3 triplets do not code for any amino acid.
These are called ‘stop codes’ and they mark the end of a polypeptide chain.
7. What does the genetic code being non-overlapping mean?

Answer 37

The genetic code being non-overlapping means that each base in the sequence is read only once

Question 38

Features of the genetic code:
Further experiments have revealed the following features of the genetic code:
1. A few amino acids are coded for by only a single triplet.
2. The remaining amino acids are coded for by between 2 and 6 triplets each.
3. The genetic code is known as a ‘degenerate code,’ because most amino acids are coded for by more than one triplet.
4. A triplet is always read in one particular direction along the DNA strand.
5. The start of a DNA sequence that codes for a polypeptide is always the same triplet.
This codes for the amino acid methionine.
If this first methionine molecule does not form part of the final polypeptide, it is later removed.
6. 3 triplets do not code for any amino acid.
These are called ‘stop codes’ and they mark the end of a polypeptide chain.
7. The genetic code being non-overlapping means that each base in the sequence is read only once.
Therefore, 6 bases numbered 123456 are read how, rather than as triplets 123, 234, 345, 456?

Answer 38

Therefore, 6 bases numbered 123456 are read:
1. As triplets 123 and 456
,rather than
2. As triplets 123, 234, 345, 456

Question 39

Features of the genetic code:
Further experiments have revealed the following features of the genetic code:
1. A few amino acids are coded for by only a single triplet.
2. The remaining amino acids are coded for by between 2 and 6 triplets each.
3. The genetic code is known as a ‘degenerate code,’ because most amino acids are coded for by more than one triplet.
4. A triplet is always read in one particular direction along the DNA strand.
5. The start of a DNA sequence that codes for a polypeptide is always the same triplet.
This codes for the amino acid methionine.
If this first methionine molecule does not form part of the final polypeptide, it is later removed.
6. 3 triplets do not code for any amino acid.
These are called ‘stop codes’ and they mark the end of a polypeptide chain.
7. The genetic code being non-overlapping means that each base in the sequence is read only once.
Therefore, 6 bases numbered 123456 are read as triplets 123 and 456, rather than as triplets 123, 234, 345, 456.
8. Why is the genetic code universal?

Answer 39

The genetic code is universal, because, except for a few minor exceptions, each triplet codes for the same amino acid in all organisms

Question 40

Features of the genetic code:
Further experiments have revealed the following features of the genetic code:
1. A few amino acids are coded for by only a single triplet.
2. The remaining amino acids are coded for by between 2 and 6 triplets each.
3. The genetic code is known as a ‘degenerate code,’ because most amino acids are coded for by more than one triplet.
4. A triplet is always read in one particular direction along the DNA strand.
5. The start of a DNA sequence that codes for a polypeptide is always the same triplet.
This codes for the amino acid methionine.
If this first methionine molecule does not form part of the final polypeptide, it is later removed.
6. 3 triplets do not code for any amino acid.
These are called ‘stop codes’ and they mark the end of a polypeptide chain.
7. The genetic code being non-overlapping means that each base in the sequence is read only once.
Therefore, 6 bases numbered 123456 are read as triplets 123 and 456, rather than as triplets 123, 234, 345, 456.
8. The genetic code is universal, because, except for a few minor exceptions, each triplet codes for the same amino acid in all organisms.
What is this indirect evidence for?

Answer 40

This is indirect evidence for evolution

Question 41

Much of the DNA in eukaryotes does not code for what?

Answer 41

Much of the DNA in eukaryotes does not code for polypeptides

Question 42

Much of the DNA in eukaryotes does not code for polypeptides.
Example

Answer 42

For example, between genes there are non-coding sequences made up of multiple repeats of base sequences

Question 43

Much of the DNA in eukaryotes does not code for polypeptides.
For example, between genes there are non-coding sequences made up of multiple repeats of base sequences.
Even within genes, what do only certain sequences code for?

Answer 43

Even within genes, only certain sequences code for amino acids

Question 44

Much of the DNA in eukaryotes does not code for polypeptides.
For example, between genes there are non-coding sequences made up of multiple repeats of base sequences.
Even within genes, only certain sequences code for amino acids.
What are these coding sequences called?

Answer 44

These coding sequences are called exons

Question 45

Much of the DNA in eukaryotes does not code for polypeptides.
For example, between genes there are non-coding sequences made up of multiple repeats of base sequences.
Even within genes, only certain sequences code for amino acids.
These coding sequences are called exons.
Within the gene, what happens to these exons?

Answer 45

Within the gene, these exons are separated by further non-coding sequences called introns

Question 46

Much of the DNA in eukaryotes does not code for polypeptides.
For example, between genes there are non-coding sequences made up of multiple repeats of base sequences.
Even within genes, only certain sequences code for amino acids.
These coding sequences are called exons.
Within the gene, these exons are separated by further non-coding sequences called introns.
What do some genes code for?

Answer 46

Some genes code for:

1. Ribosomal RNA
2. Transfer RNA