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2. Protein Synthesis
2. Protein Synthesis
Important Molecules in Making Protein!
DNA – stays in nucleus!
The RNA’s – move from nucleus to cytoplasm•mRNA•tRNA•rRNA
Amino acids – stay in cytoplasm
Glycine
Alanine
Valine
Leucine
Isoleucine
Serine
Cysteine
Methionine
Proline
Aspartic acid
Asparagine
Glutamic acid
Glutamine
Histidine
Lysine
Arginine
Phenylalanine
Tyrosine
Steps in making a ProteinA. Transcription - in nucleus
B.Translation – in cytoplasm
A. Transcription - from DNA to mRNA
• Starts making an mRNA copy using one strand of DNA as a template
•Takes place in nucleus of cell
• An enzyme (RNA polymerase)unzips DNA
LOOK!
Making mRNA – Transcription cont.
• Next, mRNA molecules are edited so that final sequence only contains protein-coding
information
•Each 3 letters in DNA (ex. ATG, CTA) directs a particular 3 letters to be formed in mRNA (ex. UAC, GAU) Remember, this is RNA! U not T!
•Each mRNA triplet = codon
“Mature” mRNA oozes out of nucleus into cytoplasm.
Editing mRNA Transcripts
• Exons remainNEXT…
•Editing of mRNA transcript begins with capping of “sticky ends” (G/polyA caps)•Introns spliced out
Example: Transcribing to mRNA
• DNA strand is split by enzymes.• mRNA strand forms from DNA template with help from RNA polymerase (replace T
with U)
A T A G C C G A T A T
T A T C G G C T A T A
U A U C G G C U A U A
2. Translation• Decoding of mRNA into protein takes
place on ribosomes in cytoplasm
• Another tRNA attaches with another amino acid coded for by mRNA
•A tRNA carrying an amino acid attaches to mRNA at a “start” codon = A U G
• mRNA attaches to ribosome
Translation cont.• Amino acids attach to one another by peptide
bonds.
•Protein continues to grow until “stop” codon reached.
• Old tRNA leaves ribosome, new tRNA comes in.
• “Polypeptide” or protein lengthens
LOOK!
MORE!
• OK, so how do these codons direct a certain amino acid to be brought to the growing protein???
• Given the following mMRA sequence, what are the amino acids it codes for?
A U G A A C C G C A U U U A AMET
“Start”
ASN ARG ILE STOP
• After translation proteins are ready to be used by the cell or body
• If the protein specific for building cell structure or metabolism is damaged, you can expect an abnormal cell.
• Remember! Whenever a cell puts its genetic code into action; it is making precisely those proteins that it requires, thus…
Mutation Buzzwords…• Point mutation (within gene)
• Frameshift mutation (within gene)= Change the reading frame (codons) of a nucleotide sequence.
• Chromosomal mutation(affecting part or whole chromosome)
Point Mutations
• Substitution = 1 base pair is substituted for another resulting in different “aa” coded for .
• Ex. cct (in DNA) = gga (in mRNA) = glycine act = uga = stop• Ex. Sickle cell anemia. Valine (gtg) substituted
for glutamate (gag) causes hemoglobin molecule to shrink and become distorted.
Frameshift Mutations
• Deletion = loss of one or several nucleotides in DNA sequence
ccgatt -> cgctt ggcuaa -> gcgaa
= glycine and stop = alanine and ?
• Insertions= addition of one or several nucleotides in DNA sequence
ccgatt -> ccgagattggcuaa -> ggcucuaa
• =glycine and stop = glycine+serine+junk
Ex. Inversion ccgatt -> cagctt
ggcuaa -> gucgaa = glycine and stop = valine and
glutamateEx. Duplication
ccgatt -> ccgagattggcuaa -> ggcucuaa
• =glycine and stop = glycine+serine+junk
•Deletion = deleted base or sequence (Cri du Chat)
Chromosomal Mutations• Nondisjunction = chromosomes don’t separate
after meiosis (Down’s Syndrome, Patau’s)
Translocations = pieces of DNA from one chromosome being inserted into another chromosome. (chronic myelogenous leukemia)
Name that Mutation!
TGAGGACTCCTC normal gene
TGAGGACACCTC abnormal gene
Sickle cell anemia/point mutation/missense
TGCGTCATA normal
TGCATCATA abnormal
Cystic fibrosis/point mut/nonsense
TCGAAACCGCCGCCGCCGCCGCCGAATTAT normal
TCGAAACCGCCGCCGCCGCCGCCGCCGCCGCCGCCGCCGCCGCCGCCGCCGCCGCCGCCGCCGCCGCCGCCGCCGCCGCCG…300more..AATTAT abnormal
Fragile x syndrome/insertion/duplication/expanding duplication mutation
Name the three types of RNA.
What is an exon?
Change the DNA sequence T T A T A A T T C C T A G into a rough mRNA transcript.
Which enzyme attaches free nucleotides to an open strand of DNA in replication?
