Necessary Components for Translation

1
Necessary Components for Translation

• Messenger RNA (mRNA)
• Encodes for a specific protein sequence.
• Variable length (depending on protein size).
• Information is read in triplets (codons) 64
  possible codons (4 x 4 x 4 64 43) 61 codons
  specify amino acids 3 codons are termination
  signals.

2
mRNA is complementary to DNA and read in triplets
(codons)
3
Necessary Components for Translation

• 2. Transfer RNA (tRNA)
• Brings one amino acid at a time to the growing
  polypeptide chain.
• Small molecule (70 to 90 nucleotides).
• Forms a cloverleaf structure.
• Anticodon Base pairs to mRNA codon during
  translation.
• Amino acid binding site At 3 end of molecule.

4
Transfer RNA (tRNA) Carries Amino Acids to the
Growing Polypeptide Chain
5
Necessary Components for Translation

• 3. Ribosomal RNA (rRNA)
• Ribosome is the site of protein synthesis.
• Facilitates coupling of mRNA to tRNA.
• Huge molecule Large and small subunits must
  assemble for translation.
• Ribosome composition 60 rRNA and 40 protein
• Transfer RNA (tRNA) Carries Amino Acids to the
  Growing Polypeptide Chain

6
Ribosome is the Site of Translation
7
STEPS OF TRANSLATION

1. INITIATION Messenger RNA (mRNA) and ribosome
   come together.Transfer RNA (tRNA) Carrying first
   amino acid (methionine) has anticodon which binds
   to start codon (AUG).
2. ELONGATION One amino acid at time is added and
   linked to growing polypeptide chain by a peptide
   bond.
3. TERMINATION-Stop codons UAA, UAG, or UGA
   Ribosome/mRNA complex dissociates.

8
Translation Initiation at Start Codon
9
Translation During Elongation one Amino Acid is
Added at a Time
10
Elongation Ribosome Travels Down mRNA, Adding
One Amino Acid at a Time
11
Termination Once Stop Codon is Reached, Complex
Disassembles
12
(No Transcript)
13
(No Transcript)
14
Mutations

• DNA replication is never 100 accurate.
• Bases may be inserted, deleted, or mismatched
  during replication.
• Mutations are permanent changes in DNA.
• Any mistakes that cause changes in the nucleotide
  sequence of DNA.
• Mutations may be either harmful, beneficial, or
  have no effect on a cell or individual.

15
Mutations

• There are several possible types of mutations
• Substitution mutation One nucleotide is replaced
  by another. May result in
• 1. Missense Different amino acid. May or may
  not have serious consequences. Example Sickle
  cell anemia.
• 2. Nonsense Stop codon. Protein is truncated.
  Usually has serious consequences.
• 3. Silent No change in amino acid. No
  consequence.

16
Missense Mutation in Sickle Cell Anemia
Base substitution results in a single amino acid
change Glu ---gt Val
17
Mutations

• 2. Frameshift Mutation Nucleotides which are
  inserted or deleted may change the genes reading
  frame. Usually serious, because entire protein
  sequence after mutation may be disrupted.

18
Effects of Different Types of Mutations