1. How cells follow DNA directions on how to make proteins
Protein Synthesis
How cells follow DNA directions on how to make
proteins

2. DNA = the directions in code
Each chain of nucleotides is a line of code
Each chain contains directions for making many different proteins
Each set of directions is
a gene
1 gene = 1 protein =1 trait

3. Steps in making a protein
1) Copy the Directions for one protein onto RNA
(one gene)
Transcription
2) Use the RNA directions to make a protein
Translation

4. 1) Transcription
A) RNA polymerase scans the DNA to find the gene it needs to copy
B) RNA polymerase has 4 jobs
1) unwind the DNA double helix
2) breaks hydrogen bonds to separate chains
3) match RNA nucleotides to the DNA gene
4) fuse the RNA nucleotides together to make a chain of RNA

5. The chain of RNA that is made is called mRNA
Or messenger RNA

6. Messenger RNA Carries coded directions out into the cell.
Where mRNA binds to a ribosome.

7. 2) Translation A) Translates nucleotide code of RNA into
the amino acid code of a protein
B) Takes place in the cytoplasm
C) Is done by a ribosome

8. mRNA
mRNA = chain of nuclotides that make up the coded directions for making the protein
Every 3 nuclotides of mRNA is a codon
Each codon is the code for 1 amino acid

10. Ribosomes Made of 2 subunits.
Subunits bind onto mRNA chain at start codon
3 codons at a time are inside the ribosome
E is for Exit
Codons in P and A sites are the ones being read

11. tRNA bring amino acids to the ribosome
Match the correct amino acid in place by matching their
anti-codon to the
mRNA codon
Fit into the E, P and A sites

12. tRNA Each tRNA only picks up ONE kind of amino acid
tRNA drops off amino acids at the ribosome then moves back into the cytoplasm to pick up another amino acid(but always the same kind)
aminoacyl-tRNA synthetase enzymes bind aa to tRNA

13. Steps to Translation A) Initiaion 1) Ribosome subunits bond to mRNA
2) tRNA that matches start codon binds at site P

14. 3) tRNA that matches 2nd codon binds at site A
B) Elongation
3) tRNA that matches 2nd codon binds at site A
4) ribosome attaches the 2 amino acids those tRNAs carry to each other by a
peptide bond

15. wobble effect
The last base in the anti-codon has some flexibility in what it binds to (wobble room)
So anticodon AGU could bind to UCA or UCG

16. 5) Ribosome moves down mRNA chain by
one codon
6) the first tRNA
Moves into the E
site and exits
the ribosome

17. 7) the next tRNA moves into place

18. Termination 8) Ribosome moves down mRNA to stop codon
9) Release factors bind to stop codon instead of a tRNA
10) Ribosome, mRNA, tRNAs and protein all break apart

19. Mutations= changes in a cell’s DNA
Caused by:
1) spontaneous errors
2) mutagens: chemicals/radiation
Can happen in body cells (somatic cells) or
In reproductive cells (egg & sperm)

20. Somatic cell mutations
May cause no change = if mutated gene is one that is not use by that particular cell
May cause cell to die
May cause cancer
Not passed on to children

21. Thymine dimer

22. Reproductive Cell or Early Embryo Cell Mutations
Child with mutation
Every cell of the child is mutated
May cause miscarriage
May cause a genetic disorder in child
May have no effect at all

23. 2 types of mutation Gene mutation = DNA coding error
may be a missense mutation where the codons code for the wrong aa ….
or nonsense where stop codon or partial codon
Chromosome Mutation = change in chromosome number, missing or extra chromosome pieces.

24. Gene Mutations
1) point mutations (substitutions) – change only 1 base pair
a) substitution of 1 nucleotide for another
b) ATT becomes ATG..(missense)
c) may not cause any change = silent mutation
d) may change 1 amino acid
e) could be nonsense only if codes for stop
e) can cause disorder

25. 2) Frameshift mutations- change all the codons
a) insertion
b) deletion
c) THE FAT CAT = HEF ATC AT
d) most always ruins protein

26. 3) tandem repeats – codons repeated over & over
most often ruins protein
more repeats = more problems

27. Transcripts Transcript = chain of RNA as copied from DNA template
Pre-mRNA = a transcript that will become mRNA
Other transcripts become tRNA or rRNA

28. Transcript processing
Pre-mRNA transcript has a cap added to 5’ end
cap facilitates exit through nuclear pore
cap aids in translation initiation
cap is added to a short UTR on 5’ end of pre-mRNA transcript (untranslated region)
UTR is followed by the start codon

29. Poly-A tail 3’ end of transcript gets a poly-A tail added to it
Enzyme adds more A ribonucleotides
More As added make the mRNA last longer
Fewer As make the mRNA break down quicker
Breakdown starts immediately on entry to cytosol
Hydrolytic enzymes

30. RNA splicing Introns = in between coding regions of RNA
do not code for a.a.s
are cut out before mRNA leaves nucleus
bacteria do NOT have introns
Exons = have codons that are executed by translation….code for a.a.s
Introns are cut out, exons fused together

32. Alternative splicing Exons are spliced together in different orders
To make different proteins

33. spliceosome Complex of proteins and small RNAs Remove introns
Joins exons in proper order
RNAs in spliceosome are Ribozymes…
RNA enzymes
Sometimes the intron being removed IS the ribozyme

34. Evidence for RNA before DNA
RNA can act as its own enzyme
RNA polymerase can initiate polymerization on its own
DNA polymerase can only start polymerization at a primer
That is created by RNA polymerase

35. Post-translational modification
Amino acid modification – add functional groups
Trim aa from cap end
Cleave polypeptide into pieces
Join 2 polypeptide into quaternary structure
with disulfide bonds

36. Protein location w/i the cell
All translation begins in cytoplasm
For proteins destined for endomembrane system
(ER, golgi, lysosome, plasma membrane)
OR proteins produced for secretion (insulin)
The first few aa at leading end of polypeptide = signal peptide
Signal peptide binds to a Signal Recognition Particle (SRP)
SRP escorts ribosome to receptor protein on ER