1. From DNA to proteins
BioH Chapter 13

2. The BIG picture – Gametes to genes

3. DNA - RNA comparison DNA RNA Monomer Sugar Bases used Usual location
Characteristic
Monomer
Sugar
Bases used
Usual location
Function
Structure
Nucleotide (P-S-B)
Deoxyribose
A,T,C,G
Nucleus only
Carries/transfers genetic info
Double strand
Nucleotide (P-S-B)
Ribose
A,U,C,G
Nucleus AND cytoplasm
Carries/transfers genetic info AND PROTEIN SYNTHESIS
Single strand
Need to know entire chart

4. Transcription The process of using a DNA template to make RNA
Video – start at 2:51, go to 4:47
(Click for video)

5. Transcription details
Enzymes used
Helicase – unwind & start strand separation
RNA polymerase – brings complementary base-matching nucleotides
Ligase – corrections and gap corrections
Promoter sequence on mRNA - signals “start” for transcribing DNA sequence into RNA sequence
ONE strand only – forming juvenile RNA
Uracil used instead of Thymine
Use Cytosine, Guanine, Adenine (same as DNA)

6. Juvenile RNA Immature RNA formed by transcription in nucleus
(juvenile RNA, pre-mRNA)
Forms mature mRNA at nuclear envelope through use of specific enzymes
Most eukaryotic genes contain base sequences that must be removed before translation can occur (introns). They will never be used to form proteins.
The RNA genes that remain (exons) form specific proteins that determine traits

7. Starting Translation NEED solve three issues:
Instructions on what specific proteins to build
Capture and provide raw material (amino acids) with which to build proteins
Place at which to build proteins
mRNA
tRNA
rRNA

8. Types of RNA
mRNA – messenger RNA – carries protein building instructions (very long)
tRNA – transfer RNA – picks up amino acid components and delivers them to a ribosome to be assembled into proteins (3 bases long)
rRNA – ribosomal RNA – attracts proteins to form a ribosome site for protein synthesis (medium length)

9. Translation
Process of translating mRNA base sequence into proteins

10. Providing the message - mRNA
Contains the coded instructions to make specific proteins (based on the nucleotides’ base sequence)
3 bases as a group (triplet) are called a codon
Use the Genetic Code charts to decipher which amino acids are coded by each codon

11. Genetic Code charts
Click on the left picture to review HOW to read the genetic code chart.
(video)
Use the mRNA codon (transcribed from DNA) to read the charts
64 codons code for only 20 different amino acid building blocks

12. Supplying raw material - tRNA
tRNA attracts amino acids in cytoplasm based “lock and key” structure
Matches the codon on the mRNA with its own 3- base anti-codon
Delivers specific amino acids to functional ribosome to build polypeptide chain (protein)
Watch entire video
(Video)

13. Ribosome Formation - rRNA
rRNA combines with other proteins to form the basis of a functional ribosome
Small subunit
Large subunit
Click on ribosome to see how subunits work. See next slide for better description of process.
(Video)

14. Finally – TRANSLATION !
Three stages: Initiation, Elongation & Termination
Initiation
Mature mRNA leaves nucleus into cytoplasm through nuclear pores
Many free amino acids, tRNA and ribosomal subunits floating in cytoplasm
Initiator tRNA (attached to the amino acid methionine) attaches to small ribosomal subunit, which then attaches to end of mRNA
mRNA moves through ribosome until reaches “start” codon (AUG) on mRNA
Large subunit attaches, forming
functional ribosome
Starts next phase = elongation
Initiator tRNA (methionine) has a different structure than elongator tRNA (methionine) and is less common than elongator tRNA

15. More translation Elongation
The initiator tRNA anticodon-mRNA codon bond causes the next bonding site in the ribosome to attract the specific anticodon of another tRNA
A 2nd tRNA (with its amino acid) bonds with the 2nd m RNA codon
Once this happens, enzymes help form a peptide bond between the two nearby amino acids
While other enzymes break the initiator amino acid bond and the first codon-anticodon bond, releasing the intiator tRNA and leaving Methionine to form a peptide bond with the second amino acid
The 2nd tRNA moves into the 1st ribosomal bonding site
A 3rd tRNA is attracted to the open
ribosomal bonding site, allowing the
process to continue
This process continues until a “STOP”
codon is read, initiating the last phase
= termination

16. Translation is terminated
Termination
The mRNA codon UAA, UAG or AGA (“STOP”) occupies the second ribosomal bonding site
No tRNA anticodon bonds with these codons
This signals the synthesis process to stop
The polypeptide chain (protein) is released from the ribosome
The two ribosomal subunits separate
We have PROTEINS!
Click on the picture to view a video of translation.
Multiple ribosomes can attach to a single mRNA forming “polysomes” that can produce multiple proteins from one strand of mRNA.
NEXT?
Free-floating proteins
Golgi apparatus packaging
Enter ER for transport

17. Problems – Gene Mutations
Point Mutations – single base-pair change
Substitution – one base substituted for the correct one
May result in only one amino acid mistake – protein may still function correctly
Frameshift Mutations
Insertion – extra base inserted
Deletion – base is omitted
Results in all codons after mutation
to be incorrect and may cause protein
to malfunction

18. Problems – Gene Mutations
Point mutations – single base changes
Deletion – base omitted
Insertion – extra base inserted
Substitution – one base substituted for the correct one
Transposition – DNA segments transposed (exchanged) with another
Mutation causes
Spontaneous
Exposure to mutagens (UV, gamma & X-rays)
Natural & synthetic chemicals

19. Significance and causes of gene mutations
Importance
Many, if not most, mutations are neutral – causing little or no effect on protein function
Can be harmful, causing genetic disorders – cystic fibrosis, sickle cell disease, cancers, HIV tolerance
Can be beneficial, evolutionary changes have come about due to positive mutations that allow organisms to better survive their environment
Click on apple to watch video about DNA mutations
Causes
Spontaneous
Exposure to mutagens
(UV, gamma & X-rays)
Natural & synthetic carcinogenic chemicals
(video)

20. The whole process
Click to watch overview of DNA transcription and protein assembly