8.1: Genes and the triplet code Flashcards
Codons
Codons are triplets of base pairs
Some of the roles of proteins in our bodies
Some of the roles of proteins in our bodies are as:
- Enzymes
- Channel proteins
- Carrier proteins
The genetic code is a triplet code.
What does this mean?
This means that 3 bases code for one amino acid
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?
Polypeptides make up proteins
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?
Polypeptides make up proteins and so genes determine the proteins of an organism
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?
If there is a mutation, that protein could become non-functional
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?
As enzymes control chemical reactions, they are responsible for an organism’s:
- Development
- Activities
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?
Genes, along with environmental factors, determine:
1. The nature
2. The development
of all organisms
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?
A gene is a section of DNA at a particular position, called a locus, on a DNA molecule
Gene
A gene is a base sequence of DNA that codes for:
1. The amino acid sequence of a polypeptide
Or,
2. A functional RNA
A gene is a base sequence of DNA that codes for the amino acid sequence of a polypeptide or a functional RNA, including what?
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
DNA codes for amino acids, but what is it made up of?
DNA:
1. Codes for amino acids
,but
2. It is made up of nucleotides
What is the sequence of amino acids coded for by DNA?
The sequence of amino acids coded for by DNA is the primary structure of a protein
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?
It is the primary structure that gives rise to the tertiary structure
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?
It is the primary structure that gives rise to:
- The tertiary structure
- Hence the shape of the protein
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?
So DNA indirectly codes for the shape of proteins
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?
So DNA indirectly codes for the shape of proteins, including enzymes
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?
Only 20 different amino acids occur regularly in proteins
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?
Each amino acid must have its own code of bases on the DNA
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?
Only 4 different bases (adenine, guanine, cytosine and thymine) are present in DNA
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?
If each base coded for a different amino acid, then only 4 different amino acids could be coded for
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?
Using a pair of bases, (4²) 16 different codes are possible, which is still inadequate
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?
3 bases produce (4³) 64 different codes
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?
3 bases produce (4³) 64 different codes, more than enough to satisfy the requirements of 20 amino acids
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?
As the code has 3 bases for each amino acid, each one is called a triplet
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?
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
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?
A few amino acids are coded for by only a single triplet
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?
The remaining amino acids are coded for by between:
1. 2
2. 6
triplets each
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?’
The genetic code is known as a ‘degenerate code,’ because most amino acids are coded for by more than one triplet
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?
A triplet is always read in one particular direction along the DNA strand
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?
The start of a DNA sequence that codes for a polypeptide is always the same triplet
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?
This codes for the amino acid methionine
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?
If this first methionine molecule does not form part of the final polypeptide, it is later removed
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?
3 triplets do not code for any amino acid
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?
These are called ‘stop codes’
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?
These are called ‘stop codes’ and they mark the end of a polypeptide chain
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?
The genetic code being non-overlapping means that each base in the sequence is read only once
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?
Therefore, 6 bases numbered 123456 are read:
1. As triplets 123 and 456
,rather than
2. As triplets 123, 234, 345, 456
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?
The genetic code is universal, because, except for a few minor exceptions, each triplet codes for the same amino acid in all organisms
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?
This is indirect evidence for evolution
Much of the DNA in eukaryotes does not code for what?
Much of the DNA in eukaryotes does not code for polypeptides
Much of the DNA in eukaryotes does not code for polypeptides.
Example
For example, between genes there are non-coding sequences made up of multiple repeats of base sequences
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?
Even within genes, only certain sequences code for amino acids
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?
These coding sequences are called exons
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?
Within the gene, these exons are separated by further non-coding sequences called introns
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?
Some genes code for:
- Ribosomal RNA
- Transfer RNA
