1. 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

2. DNA’s Purpose
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.

3. Differences between DNA and RNA
Structure:
Single-stranded
Sugar: Ribose
Bases:
Adenine
Guanine
Cytosine
Uracil
DNA
Structure:
Double stranded
Sugar: Deoxyribose
Bases:
Adenine
Guanine
Cytosine
Thymine

4. RNA Ribonucleic acid Single-stranded Sugar is ribose
Thymine is replaced by URACIL
3 major types in living cells
Messenger RNA (mRNA)
carries information from DNA to ribosome
Transfer RNA (tRNA)
Carries amino acids to ribosome to make protein
Ribosomal RNA (rRNA)
Makes up ribosomes; site of protein synthesis.
located on Rough ER and in cytoplasm

5. Bring amino acids to ribosome
RNA
can be
Messenger RNA
Ribosomal RNA
Transfer RNA
also called
which functions to
also called
which functions to
also called
which functions to
mRNA
Carry instructions
rRNA
Combine
with proteins
tRNA
Bring amino acids to ribosome
from to
to make up
DNA
Ribosome
Ribosomes

6. How do you get from DNA to Proteins?
TRANSCRIPTION – the synthesis of RNA under the direction of DNA
TRANSLATION – the actual synthesis of a protein, which occurs under the direction of mRNA

7. Transcription
From DNA to RNA

8. Transcription- Where does this happen?
Where is the DNA?

9. Transcription- how RNA is made
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

10. Translation
From RNA to Protein

11. Translation- Where does this happen?
Where is the DNA?
Protein synthesis – the manufacture of proteins
Where are proteins made in the cell?

12. Translation- how proteins are made
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

13. Genetic Code
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

14. Codon (cont’d) 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

15. Codons (cont’d) AUG – start codon or Methionine
UAA, UAG, UGA – stop codons; code for nothing; like the period at the end of a sentence

16. Protein formation Amino acids link together to form a protein
The new protein could become cell part, an enzyme, a hormone etc.

17. Translation
CODON
ANTI CODON

18. SO: Methionine-Aspartic acid-Glutamine-stop 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

19. 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

20. What if things go wrong? 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

21. Gene Mutations
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!)

22. Deletion
Substitution
Insertion

23. Chromosomal Mutations
Change in the number or structure of chromosomes
Ex. – Deletion, Duplication, Inversion, and Translocation

24. Deletion
Duplication
Inversion
Translocation