Download Protein Synthesis Section 3 Transcription and Translation

Watson and Crick discovered the
structure of DNA, but what remained a
mystery is how DNA served as a genetic
code for the making of proteins.
Animation
 DNA has genes that code for the synthesis
(creation) of specific PROTEINS
 Here’s the problem…
 Where is DNA located?
 Nucleus
 Where does Protein Synthesis occur?
 At ribosomes in the cytoplasm
 Can DNA ever leave the nucleus?
 No.
DNA
 Structure:
 Double stranded
RNA
 Structure:
 Single-stranded
 Sugar: Deoxyribose
 Sugar: Ribose
Bases:
 Adenine
 Guanine
 Cytosine
 Thymine
Bases:
 Adenine
 Guanine
 Cytosine
 Uracil
 Ribonucleic acid
 Single-stranded
 Sugar is ribose
 Thymine is replaced by URACIL
3 major types in living cells
1) Messenger RNA (mRNA)
o carries information from DNA to ribosome
2) Transfer RNA (tRNA)
o Carries amino acids to ribosome to make protein
3) Ribosomal RNA (rRNA)
o Makes up ribosomes; site of protein synthesis.
o located on Rough ER and in cytoplasm
RNA
can be
Messenger RNA
Ribosomal RNA
which functions to
also called
mRNA
Carry instructions
also called
which functions to
rRNA
Combine
with proteins
from
to
to make up
DNA
Ribosome
Ribosomes
Transfer RNA
also called
which functions to
tRNA
Bring
amino acids to
ribosome
TRANSCRIPTION – the synthesis of
RNA under the direction of DNA
TRANSLATION – the actual synthesis of a
protein, which occurs under the direction of
mRNA
From DNA to RNA
Where is the DNA?
 location= nucleus
 RNA polymerase runs along DNA
strand in nucleus and makes RNA
(mRNA)
 mRNA = messenger RNA (sends
message outside of nucleus)
 mRNA leaves nucleus through a
nuclear pore and meets up with a
ribosome (rRNA) in the cytoplasm
From RNA to Protein
Where is the DNA?
Protein synthesis – the
manufacture of
proteins
Where are proteins
made in the cell?
 location= ribosome in
cytoplasm
 Once mRNA is at a ribosome
(rRNA), amino acids are
assembled to make proteins
 Transfer RNA (tRNA) brings
the appropriate amino acid
to the growing protein chain
 Genetic code – the language of mRNA instructions
(blueprints)
 Read in three letters at a time
 Each letter represents one of the nitrogenous bases: A, U, C, G
 Codon found on mRNA; consists of three bases (one
right after the other)
 64 codons for 20 amino acids
mRNA carries the codon (three base sequence that codes for an
amino acid)
tRNA carries the anticodon which pairs up with the codon
tRNA brings the correct amino acid by reading the genetic code
 For example, consider the
following RNA sequence:
UCGCACGGU
The sequence would be read
three base pairs at a time:
UCG – CAC – GGU
The codons represent the
amino acids:
Serine – Histidine - Glycine
 AUG – start codon or
Methionine
 UAA, UAG, UGA – stop
codons; code for nothing;
like the period at the end of
a sentence
 Amino acids link
together to form a
protein
 The new protein
could become cell
part, an enzyme, a
hormone etc.
CODON
ANTI
CODON
 Say the mRNA strand reads:
 mRNA (codon)
AUG–GAC–CAG-UGA
 tRNA (anticodon) UAC-CUG-GUC-ACU
 tRNA would bring the amino acids:
 Methionine-Aspartic acid-Glutamine-stop
SUMMARY
1)mRNA is transcribed in the nucleus and
leaves the nucleus to the cytoplasm
2) mRNA attaches to the ribosome
3) The codon on the mRNA is read by the
anticodon on the tRNA
4) tRNA brings the amino acid as it reads
mRNA
5) The amino acids are joined together to form
a polypeptide (protein)
6) When a stop codon is reached (UAA, UAG,
UGA) protein synthesis stops
 MUTATION!!!
 If transcription or translation were to copy the
wrong sequence, the incorrect amino acid could be
added
 This would change the overall protein structure
and could make the protein ineffective
 Example: Sickle cell anemia is caused by a single amino
acid difference in the hemoglobin protein sequence
 Point Mutations – only occur at a single point in the DNA
sequence – only changes a few amino acids
 Frameshift Mutations – shift the entire “reading frame” –
change ALL the amino acids
 Substitution – one base replaces another
 Insertion – an extra base is inserted
 Deletion – loss of a single letter (makes entire base
disappear!)
Substitution
Insertion
Deletion
 Change in the number or structure of chromosomes
 Ex. – Deletion, Duplication, Inversion, and
Translocation
Deletio
n
Duplication
Inversion
Translocation