Molecular genetics
Genetic code
Triplet code: (DNA) 3 consecutive bases, ×64 codes
Codon: (mRNA: U instead of T)
- read in non overlapping manner: - each codon code for 1 amino acid
no sharing of bases between only
consecutive codons - degenerate genetic code: most
amino acids are coded by >1
- universal: same codon code for
codons
same amino acid in all organisms - decrease harm from
mutation on 3rd nitrogenous
base
- AUG (code for amino acid
Methionine): start signal marking
beginning of base sequence
encoding a polypeptide
- UAA UAG UGA (these 3 do not
code for any amino acids): stop
signals marking end of base
sequence encoding a polypeptide
Protein synthesis
Transcription: template strand (DNA): one of the two strands used to make RNA
DNA > mRNA - mRNA complementary to its base sequence
coding strand/ non-template strand (DNA): the other strand
DNA is too large - same base sequence as mRNA produced, except T is replaced
to leave the by U
nucleus so let’s
just make a copy
of what we need 1. RNA polymerase binds to DNA at the start of a gene (promoter
and take that to region), breaking hydrogen bonds between base pairs. The 2
the cytoplasm for DNA strands unwind.
protein synthesis
2. Free ribonucleotides attracted to exposed bases in template
choco-chip cookie strand through complementary base pairing. RNA polymerase
recipe from catalyses the joining of adjacent ribonucleotides for synthesis of
grandma’s mRNA.
cookbook copied 3. Once the whole gene has been transcribed, mRNA separates
to index card >:)
from the template strand of DNA and leaves the nucleus. DNA
winds back into a double helix.
Translation: Messenger RNA (mRNA): carries instructions for assembling
mRNA > polypeptides from DNA in nucleus to cytoplasm <codon>
polypeptides Ribosomal RNA (rRNA): combines w proteins to form ribosomes which
assemble polypeptides
- Ribosome can move along an mRNA molecules repeatedly for
, synthesis of a number of polypeptides
- Many ribosomes move along the same mRNA molecule at the
same time
- > many polypeptides made in a short period of time
Transfer RNA (tRNA): carries amino acids from cytoplasm to ribosomes
for assembling polypeptides <anticodon: 3 bases, pair w mRNA codon>
1. The end with start codon AUG of an mRNA molecule attaches to
a ribosome.
2. A specific amino acid is carried to the ribosome by a tRNA
molecule as an amino acid tRNA complex. The anticodon on
tRNA binds to the first codon on the mRNA as they are
complementary to each other.
3. The 2 amino acids are then joined by a peptide bond.
4. The ribosome moves along to add amino acids to the growing
polypeptide chain, one at a time, while releasing the previous
tRNA into the cytoplasm to carry more amino acids.
5. Finally, the ribosome reaches a stop codon. The polypeptide
formed is released from the ribosome.
Polypeptides > Polypeptide chains coils and folds into a protein due to the
proteins intramolecular bonds between different amino acids in the polypeptide.
Proteins made @robosomes on RER:
- secreted outside cell: digestive enzymes, hormones, antibodies
- embedded in cell membrane: carrier proteins, channel proteins
Proteins made @free floating ribosomes
- remain in cytoplasm: enzymes that catalyse reactions in cell
Gene expression
Each cell contains all the genes required for making all the proteins in our body
- In diff types of cells, diff sets of genes are expressed
- A particular type of cell has a diff pattern of gene expression at diff time
- >> produce diff proteins to perform diff functions
Epigenetics
- Modifications to DNA affecting the phenotype of a person without changing the
genotype to regulate gene expression
- May be related to the development of diseases (eg. cancer, obesity)
- Factors influencing epigenetic modifications: diet, exercise, stress
Mutations
- Sudden and permanent change in DNA of an organism
Gene mutations Chromosome mutations
- Changes in base sequence of DNA - Changes in structure/number of
on a gene chromosomes
Genetic code
Triplet code: (DNA) 3 consecutive bases, ×64 codes
Codon: (mRNA: U instead of T)
- read in non overlapping manner: - each codon code for 1 amino acid
no sharing of bases between only
consecutive codons - degenerate genetic code: most
amino acids are coded by >1
- universal: same codon code for
codons
same amino acid in all organisms - decrease harm from
mutation on 3rd nitrogenous
base
- AUG (code for amino acid
Methionine): start signal marking
beginning of base sequence
encoding a polypeptide
- UAA UAG UGA (these 3 do not
code for any amino acids): stop
signals marking end of base
sequence encoding a polypeptide
Protein synthesis
Transcription: template strand (DNA): one of the two strands used to make RNA
DNA > mRNA - mRNA complementary to its base sequence
coding strand/ non-template strand (DNA): the other strand
DNA is too large - same base sequence as mRNA produced, except T is replaced
to leave the by U
nucleus so let’s
just make a copy
of what we need 1. RNA polymerase binds to DNA at the start of a gene (promoter
and take that to region), breaking hydrogen bonds between base pairs. The 2
the cytoplasm for DNA strands unwind.
protein synthesis
2. Free ribonucleotides attracted to exposed bases in template
choco-chip cookie strand through complementary base pairing. RNA polymerase
recipe from catalyses the joining of adjacent ribonucleotides for synthesis of
grandma’s mRNA.
cookbook copied 3. Once the whole gene has been transcribed, mRNA separates
to index card >:)
from the template strand of DNA and leaves the nucleus. DNA
winds back into a double helix.
Translation: Messenger RNA (mRNA): carries instructions for assembling
mRNA > polypeptides from DNA in nucleus to cytoplasm <codon>
polypeptides Ribosomal RNA (rRNA): combines w proteins to form ribosomes which
assemble polypeptides
- Ribosome can move along an mRNA molecules repeatedly for
, synthesis of a number of polypeptides
- Many ribosomes move along the same mRNA molecule at the
same time
- > many polypeptides made in a short period of time
Transfer RNA (tRNA): carries amino acids from cytoplasm to ribosomes
for assembling polypeptides <anticodon: 3 bases, pair w mRNA codon>
1. The end with start codon AUG of an mRNA molecule attaches to
a ribosome.
2. A specific amino acid is carried to the ribosome by a tRNA
molecule as an amino acid tRNA complex. The anticodon on
tRNA binds to the first codon on the mRNA as they are
complementary to each other.
3. The 2 amino acids are then joined by a peptide bond.
4. The ribosome moves along to add amino acids to the growing
polypeptide chain, one at a time, while releasing the previous
tRNA into the cytoplasm to carry more amino acids.
5. Finally, the ribosome reaches a stop codon. The polypeptide
formed is released from the ribosome.
Polypeptides > Polypeptide chains coils and folds into a protein due to the
proteins intramolecular bonds between different amino acids in the polypeptide.
Proteins made @robosomes on RER:
- secreted outside cell: digestive enzymes, hormones, antibodies
- embedded in cell membrane: carrier proteins, channel proteins
Proteins made @free floating ribosomes
- remain in cytoplasm: enzymes that catalyse reactions in cell
Gene expression
Each cell contains all the genes required for making all the proteins in our body
- In diff types of cells, diff sets of genes are expressed
- A particular type of cell has a diff pattern of gene expression at diff time
- >> produce diff proteins to perform diff functions
Epigenetics
- Modifications to DNA affecting the phenotype of a person without changing the
genotype to regulate gene expression
- May be related to the development of diseases (eg. cancer, obesity)
- Factors influencing epigenetic modifications: diet, exercise, stress
Mutations
- Sudden and permanent change in DNA of an organism
Gene mutations Chromosome mutations
- Changes in base sequence of DNA - Changes in structure/number of
on a gene chromosomes
