Protein synthesis notes
E1. PROTEIN SYNTHESIS
i) Transcription - DNA ---> mRNA
TRANSCRIPTION TRANSLATION
ii) Translation (mRNA to Protein)
- occurs with ribosomes
-small organelles composed of protein and rRNA (ribosomal RNA is transcribed in the nucleus in the Nucleolus )
i) Transcription - DNA ---> mRNA
- DNA unzips (as in replication) but only at a specified spot (a gene).
-(only a portion of the DNA unzips)
- RNA is transcribed (copied from the DNA in the nucleus)
-Uracil (U) replaces Thymine (T)
-RNA nucleotides match up with their complementary DNA bases.
- only 1 side of DNA is used
- called Messenger RNA (mRNA )
- The mRNA then moves out through the nuclear pores into the cytoplasm where it is translated into an amino acid sequence.
TRANSCRIPTION TRANSLATION
ii) Translation (mRNA to Protein)
- occurs with ribosomes
-small organelles composed of protein and rRNA (ribosomal RNA is transcribed in the nucleus in the Nucleolus )
- ribosomes are usually found on the surface of the endoplasmic reticulum (ER) or in groups (polysomes) free floating in the cytoplasm.
- they are the site of protein synthesis (Translation)
The Code - codons
- the codon is a three base unit of the mRNA
- each codon calls for a specific amino acid
eg)
CODON AMINO ACID
CCU Proline
GAA Glutamic acid
UUA Leucine
UAA STOP - end of chain
This code is universal - the same for all living things
Transfer RNA - tRNA
- carries the specific amino acid to its coded spot (codon) on the mRNA
- has an anticodon which matches the mRNA (ie: has complementary bases)
The Actual Process
INITIATION:
- Ribosome lines up with the messanger RNA at the start (AUG)
ELONGATION:
- Ribosomes move along messenger RNA reading codons and binding amino acids that are in the right place due to the transfer RNA (tRNA).
- enzyme on ribosome catalyses the peptide bond
- chain grows one amino acid at a time
TERMINATION:
- Ribosome reads "terminate" codon (UAG) and stops
- releases protein which will fold into secondary, tertiary shape
- process takes seconds up to 3 minutes
- several ribosomes may run down one mrRNA strand at one time
- mRNA disintigrates after translation is complete (some forms last longer than others, usually flagged with a total of sev. hundred Adenine bases)
MUTATIONS AND DEFECTS
Chromosome Mutation:
- they are the site of protein synthesis (Translation)
The Code - codons
- the codon is a three base unit of the mRNA
- each codon calls for a specific amino acid
eg)
CODON AMINO ACID
CCU Proline
GAA Glutamic acid
UUA Leucine
UAA STOP - end of chain
This code is universal - the same for all living things
Transfer RNA - tRNA
- carries the specific amino acid to its coded spot (codon) on the mRNA
- has an anticodon which matches the mRNA (ie: has complementary bases)
The Actual Process
INITIATION:
- Ribosome lines up with the messanger RNA at the start (AUG)
ELONGATION:
- Ribosomes move along messenger RNA reading codons and binding amino acids that are in the right place due to the transfer RNA (tRNA).
- enzyme on ribosome catalyses the peptide bond
- chain grows one amino acid at a time
TERMINATION:
- Ribosome reads "terminate" codon (UAG) and stops
- releases protein which will fold into secondary, tertiary shape
- process takes seconds up to 3 minutes
- several ribosomes may run down one mrRNA strand at one time
- mRNA disintigrates after translation is complete (some forms last longer than others, usually flagged with a total of sev. hundred Adenine bases)
MUTATIONS AND DEFECTS
Chromosome Mutation:
- A change in the physical piecing of a
chromosome
- Usually involves thousands of genes
- missing pieces
- extra pieces
- exchange of pieces
Translocation: pieces of separate chromosomes are exchanged (example above)
Deletion: Pieces become missing
Duplication: Extra pieces are copied and added
Inversion: Pieces are flipped into reverse order
Gene
- A gene is the segment of DNA on a chromosome that codes for one protein.
- The human genome (all the DNA in all 46 chromosomes in one human cell) is aprox. 3 billion base pairs. Only 10 - 15 % of this DNA is actual genes.
- Haemophilus influenzae , the first organism (a bacteria) that has had its entire genome worked out (each base!) is 1.8 million bases long.
Gene Mutation:
- a change in the nucletide sequence
- only one gene is affected
Deletion: One base is left out
- serious
- change all of the codons following it
Addition: One base is added
- serious
- change all the codons following it
Substitution: Pieces are replaced with each other.
- less serious
- only one codon is affected.
E3. Causes of Mutations:
Germinal
- can be passed on to offspring (occurs in egg/sperm cell)
- haemophilia
Stomatic Mutation
- body cell
- not inheritable
- responsible for many cancers
X-rays, Radiation, Chemicals etc. can all be mutagens
E. 4 Mutations and Genetic Disorders
- normally, chemical reactions occur in "pathways"
chromosome
- Usually involves thousands of genes
- missing pieces
- extra pieces
- exchange of pieces
Translocation: pieces of separate chromosomes are exchanged (example above)
Deletion: Pieces become missing
Duplication: Extra pieces are copied and added
Inversion: Pieces are flipped into reverse order
Gene
- A gene is the segment of DNA on a chromosome that codes for one protein.
- The human genome (all the DNA in all 46 chromosomes in one human cell) is aprox. 3 billion base pairs. Only 10 - 15 % of this DNA is actual genes.
- Haemophilus influenzae , the first organism (a bacteria) that has had its entire genome worked out (each base!) is 1.8 million bases long.
Gene Mutation:
- a change in the nucletide sequence
- only one gene is affected
Deletion: One base is left out
- serious
- change all of the codons following it
Addition: One base is added
- serious
- change all the codons following it
Substitution: Pieces are replaced with each other.
- less serious
- only one codon is affected.
E3. Causes of Mutations:
Germinal
- can be passed on to offspring (occurs in egg/sperm cell)
- haemophilia
Stomatic Mutation
- body cell
- not inheritable
- responsible for many cancers
X-rays, Radiation, Chemicals etc. can all be mutagens
E. 4 Mutations and Genetic Disorders
- normally, chemical reactions occur in "pathways"
- If Enzyme BC were mutated and nonfunctional, then compounds C and D could no be made. Clot would not form - Hemophelia
- this is an abnormal body function, or disease.
SELF QUIZ
Given the following DNA nucleotide sequence:
- this is an abnormal body function, or disease.
SELF QUIZ
Given the following DNA nucleotide sequence:
A) Give the mRNA sequence that would be transcribed from it.
B) Give the mRNA codons.
C) Give the tRNA anticodons.
D) Give the amino acid sequence that would be translated from it.
E) A mutation has inserted a G in between the two A's (1). Give the new amino acid sequence. (an addition)
F) A mutation has removed the 2nd T (2). Give the new amino acid sequence. (a deletion)
G) A mutation has changed the 3rd T to a C (3). Give the new amino acid sequence. (a substitution)
H) Given the following amino acid sequence, give a possible DNA sequence that could code for the sequence.
Lysine, Asparganine, Methionine, Glutamate, Alanine, Stop.
B) Give the mRNA codons.
C) Give the tRNA anticodons.
D) Give the amino acid sequence that would be translated from it.
E) A mutation has inserted a G in between the two A's (1). Give the new amino acid sequence. (an addition)
F) A mutation has removed the 2nd T (2). Give the new amino acid sequence. (a deletion)
G) A mutation has changed the 3rd T to a C (3). Give the new amino acid sequence. (a substitution)
H) Given the following amino acid sequence, give a possible DNA sequence that could code for the sequence.
Lysine, Asparganine, Methionine, Glutamate, Alanine, Stop.