Topic 4.1 DNA and 4.2 Protein Synthesis
Prokaryotic DNA Eukaryotic DNA
Short Long
Circular Linear
Not associated with proteins Associated with proteins (histones)
Do not have non-coding regions Have non-coding regions
Deoxyribonucleic Acid - DNA
Contains information of how to make polypeptide proteins.
These proteins then regulate cell metabolism and behaviour.
Hence DNA ‘controls’ the cell.
Chargaff’s Rule:
A purine (2 rings) always pairs with a pyrimidine (1 ring) - This keeps DNA parallel.
The purines:
- Adenine - Guanine
The pyrimidines:
- Thymine - Cytosine
DNA is..
Universal
- Every organism's DNA is made up of the same four bases.
- Every three bases form a triplet code.
, - Each triplet code determines 1 amino acid.
- It is the sequence of bases and quantity of DNA that determines the organism's characteristics.
Non-overlapping
- Each base in each triplet code is only read once.
Degenerate
- Some amino acids have more than one triplet code.
Transcription
Introns – non-coding regions
Exons – coding regions
Describe how an mRNA molecule is produced (5)
RNA polymerase binds to the promotor region
DNA ‘unzips’ (helicase) to expose the bases on the template strand
Free RNA nucleotides bind to complementary bases (uracil replaces thymine)
RNA polymerase joins the nucleotides together
Pre-mRNA released – DNA molecule rejoins
, Pre-mRNA is cut and spliced to remove the introns - mRNA
This occurs in the nucleus. The mRNA leaves through a nuclear pore and attaches to a ribosome
Compare and contrast DNA replication and transcription (5)
Similarities:
Use helicase to separate the strands
Complementary bases C and G
Polymerase form phosphodiester bonds
Differences:
One strand acts as a template in transcription and both strands in DNA replication
RNA nucleotides in transcription and DNA nucleotides in DNA replication
RNA polymerase in transcription and DNA polymerase in DNA replication
Process of Translation
mRNA leaves (nucleus) through nuclear pore and binds to a ribosome.
tRNA molecules bring specific amino acids (to ribosome)
anticodon of tRNA corresponds / complementary to codon on mRNA
two tRNA molecules can bind at a time
peptide bonds form between amino acids
tRNA detaches and collects another amino acid
ribosome moves along mRNA
the ribosome separates when it reaches a stop codon – a polypeptide chain is released.
Explain the role of tRNA in forming the primary structure of a protein (3)
tRNA carries a specific amino acid.
tRNA anti-codon binds to complementary codon.
Prokaryotic DNA Eukaryotic DNA
Short Long
Circular Linear
Not associated with proteins Associated with proteins (histones)
Do not have non-coding regions Have non-coding regions
Deoxyribonucleic Acid - DNA
Contains information of how to make polypeptide proteins.
These proteins then regulate cell metabolism and behaviour.
Hence DNA ‘controls’ the cell.
Chargaff’s Rule:
A purine (2 rings) always pairs with a pyrimidine (1 ring) - This keeps DNA parallel.
The purines:
- Adenine - Guanine
The pyrimidines:
- Thymine - Cytosine
DNA is..
Universal
- Every organism's DNA is made up of the same four bases.
- Every three bases form a triplet code.
, - Each triplet code determines 1 amino acid.
- It is the sequence of bases and quantity of DNA that determines the organism's characteristics.
Non-overlapping
- Each base in each triplet code is only read once.
Degenerate
- Some amino acids have more than one triplet code.
Transcription
Introns – non-coding regions
Exons – coding regions
Describe how an mRNA molecule is produced (5)
RNA polymerase binds to the promotor region
DNA ‘unzips’ (helicase) to expose the bases on the template strand
Free RNA nucleotides bind to complementary bases (uracil replaces thymine)
RNA polymerase joins the nucleotides together
Pre-mRNA released – DNA molecule rejoins
, Pre-mRNA is cut and spliced to remove the introns - mRNA
This occurs in the nucleus. The mRNA leaves through a nuclear pore and attaches to a ribosome
Compare and contrast DNA replication and transcription (5)
Similarities:
Use helicase to separate the strands
Complementary bases C and G
Polymerase form phosphodiester bonds
Differences:
One strand acts as a template in transcription and both strands in DNA replication
RNA nucleotides in transcription and DNA nucleotides in DNA replication
RNA polymerase in transcription and DNA polymerase in DNA replication
Process of Translation
mRNA leaves (nucleus) through nuclear pore and binds to a ribosome.
tRNA molecules bring specific amino acids (to ribosome)
anticodon of tRNA corresponds / complementary to codon on mRNA
two tRNA molecules can bind at a time
peptide bonds form between amino acids
tRNA detaches and collects another amino acid
ribosome moves along mRNA
the ribosome separates when it reaches a stop codon – a polypeptide chain is released.
Explain the role of tRNA in forming the primary structure of a protein (3)
tRNA carries a specific amino acid.
tRNA anti-codon binds to complementary codon.
