1. From Gene to Protein
Chapter 17

2. (think about what the functions of proteins are in living things…)
What do genes code for?
PROTEINS!
(think about what the functions of proteins are in living things…)
DNA
proteins
All the traits
of the organism

3. The flow of genetic information in a cell
The “Central Dogma”
The flow of genetic information in a cell
transcription
translation
DNA
RNA
protein
trait
To get from the chemical language of DNA to the chemical language of proteins requires 2 major stages:
transcription and translation
Do any organisms violate the
central dogma?
replication

4. Protein Synthesis: From gene to proteinaa a
nucleus
cytoplasm
transcription
translation
DNA
mRNA
protein
ribosome
trait

5. RNA RNA Monomers = nucleotides Ribose sugar Nitrogen Bases
uracil instead of thymine
U bonds with A
C bonds with G
Single stranded
Location: Nucleus or cytoplasm
RNA

6. Types of RNA Ribosomal RNA (rRNA) Transfer RNA (tRNA)
Major component of ribosomes
Transfer RNA (tRNA)
Folded upon itself
Carries the amino acids to the mRNA
Messenger RNA (mRNA)
Sequence of nucleotides that determines the primary sequence of the polypeptide
Made in the nucleus from the DNA: transcription
snRNA (small-nuclear “snurps”)
Forms the “spliceosomes” which are used to cut out introns from pre-mRNA
siRNA (small-interfering)
targets specific mRNA and prohibits it from being expressed

7. Transcription: DNA to mRNA
Location: Nucleus
RNA polymerase unzips DNA section and lays down nucleotides in 5’to 3’ direction.
Leaves the nucleus through the nuclear pores to find a ribosome!

8. Coding strand = this is the protein needed or “sense strand”
Template strand (noncoding) = this is the “anti-sense strand”

9. How is Transcription Started?
Transcription Factors
Cell signal to transcribe
Bind to promoter region
The “TATA Box”
Other TF’s bind
RNA polymerase can now bind
Turns gene on or off

10. Modifying the Transcript…
animation
exons = the real gene
expressed / coding DNA
introns = non-coded section
in-between sequence
Spliceosomes cut out introns with ribozymes
intron = noncoding (inbetween) sequence
eukaryotic DNA
exon = coding (expressed) sequence

11. Starting to get hard to define a gene!
Alternative Splicing
Same piece of DNA can become different proteins!
Not all the exons may make it to the final product
Intron presence can determine which exons stay or go
Increases efficiency and flexibility making proteins
Starting to get hard to define a gene!

12. Final mRNA processing for Eukaryotes
Need to protect mRNA moving to cytoplasm (enzymes in cytoplasm will attack mRNA!)
add 5 GTP cap
add poly-A tail A
3' poly-A tail
mRNA 5'
5' cap 3' G P
A’s
eukaryotic RNA is about 10% of eukaryotic gene.

13. Summing Up Transcription:

14. Understanding the Genetic Code
Code is “almost” universal amongst all organisms (evolutionary heritage)
Each CODON of mRNA = 3 nucleotides (EX: CCG, AUG)
64 different combinations possible
Only 20 amino acids exist in the human body
Some codons code for the same amino acids (degenerate or redundancy)
Sequence of codons determines the sequence of the polypeptide
(ex: Protein: AUG-CCG is NOT the same as CCG-AUG!)

15. CODON CHART You don’t need to memorize the codons (except for AUG)
Start codon
AUG
methionine
Stop codons
UGA, UAA, UAG
Strong evidence for a single origin in evolutionary theory.

16. mRNA codes for proteins in triplets
TACGCACATTTACGTACGCGG
DNA
codon
AUGCGUGUAAAUGCAUGCGCC
mRNA ?
MetArgValAsnAlaCysAla
protein

17. TRANSLATION: Reading the code from mRNA and creating a protein

18. Need: RIBOSOMES!!! Made of rRNA and proteins
Functions: Facilitates bonding of tRNA anticodon to mRNA codon to MAKE THE PROTEIN! E P A

19. Transfer RNA Contains “anticodon” Anticodons bind to codons
Some tRNA may bind with more than one codon (Supports redundancy)
“Wobble” hypothesis: anticodon with U in third position can bind to A or G

20. Translation: mRNA to Protein
Location: cytoplasm
Initiation - start codon found (AUG)
Elongation – amino acids are joined
Termination – a STOP codon is reached

21. Can you tell the story? exon intron 5' GTP cap poly-A tail
RNA polymerase
DNA
Can you tell the story?
amino acids
exon
intron
tRNA
pre-mRNA
5' GTP cap
mature mRNA
poly-A tail
large ribosomal subunit 3'
polypeptide 5'
tRNA
small ribosomal subunit E P A
ribosome

22. Protein Synthesis in Prokaryotes
Transcription & translation are simultaneous in bacteria
no mRNA editing
ribosomes read mRNA as it is being transcribed

23. Prokaryote vs. Eukaryote Differences
Prokaryotes
DNA in cytoplasm
circular chromosome
naked DNA
no introns
No splicing
Promoter & terminator sequence
Smaller ribosomes
Eukaryotes
DNA in nucleus
linear chromosomes
DNA wound on histone proteins
introns and exons
“TATA” box promoter
Transcription factors present
Walter Gilbert hypothesis:
Maybe exons are functional units and introns make it easier for them to recombine, so as to produce new proteins with new properties through new combinations of domains.
Introns give a large area for cutting genes and joining together the pieces without damaging the coding region of the gene…. patching genes together does not have to be so precise.