1. Molecular Biology
Chapter 10

2. DNA Structure

3. Nucleic Acids (Review)
Polymers made of nucleotides
Sugar-phosphate backbone (sides)
Nitrogenous bases face in (rungs)
Guanine
Adenine
Cytosine
Thymine
Uracil

4. Nucleic Acid Types (Review)
DNA
RNA
Sugar is deoxyribose
Has - H
Bases are A,C, G, and T
Double-stranded helix
Only in nucleus
Modified only by mutations
1 type
Sugar is ribose
Has - OH
Bases are A, C, G, and U
Single-stranded
Not confined to nucleus
Lots of processing and modifications
3 types

5. RNA Types Ribosomal RNA (rRNA) Messenger RNA (mRNA)
Combines with proteins to form ribosomes
Synthesize polypeptides
Messenger RNA (mRNA)
Complimentary DNA sequence
Carries DNA message from the nucleus to ribosomes
Transfer RNA (tRNA)
Transfers amino acids to ribosomes
Build polypeptide chains

6. James Watson and Francis Crick
Nobel prize for DNA double-helix model
5’ to 3’ ends
Complementary binding
Supported by Chargaff’s rules
A with T
G with C

7. Semiconservative model
Each strand of original DNA serves as a template
Nucleotides complementarily bind
1 ‘parent’ DNA strand produces 2 new ‘daughter’ strands
Occurs rapidly, both strands simultaneously

8. DNA Replication Helicase DNA polymerase DNA ligase
Unzips and separates strands
DNA polymerase
Link nucleotides to growing daughter strands
Can only bind to 3’
New strands can only grow 5’ to 3’
Leading strand – follows helicase (continuous)
Lagging strand – opposes helicase (fragmented)
DNA ligase
Links fragments together
Roles in maintenance, proofreading, and repair

9. Protein Synthesis

10. Central Dogma of Biology
transcribed
translated
DNA  RNA  protein
Francis Crick
Genes instruct, but don’t build
Transcription (same language) in nucleus
Translation (new language) in cytoplasm
mRNA codes for polypeptides

11. Transcription In the nucleus RNA polymerase binds
Separates DNA strands
Adds RNA nucleotides
Bind to 3’ end only
Builds 5’  3’
Unstable complex = immediate release
Terminator sequence releases RNA polymerase
Release pre-mRNA

12. Pre - mRNA Processing Before leaving nucleus
Introns (filler) and exons (code)
Introns removed and exons rejoined
Creates mRNA

13. Decoding Codons 4 nucleotide bases to specify 20 amino acids
Genetic instructions are based on triplet code called codons
Demonstrates redundancy, but not ambiguity
Nearly universal across species

14. Translation Within ribosomes mRNA has codon message from DNA
Translated by tRNA
mRNA sequence determines
Ribosomes facilitate addition of tRNA to mRNA

15. Ribosomes Coordinate mRNA and tRNA Composed of proteins and rRNA
Actually make polypeptides
2 subunits, large and small
Small locks mRNA
Large has 2 sites
P site holds growing polypeptide
A site holds new tRNA molecule (amino acid)

16. Initiation Small subunit binds mRNA at a start codon (AUG)
1st tRNA enters the P site carrying the amino acid met
Large subunit binds to create a ribosome
Met is in the P site
A site is empty

17. Elongation 2nd tRNA molecule into A site
Polypeptide in P site breaks off and attaches to amino acid in A site
P site tRNA leaves
Ribosome translocates
Shifts 5’ to 3’
A site tRNA to P site
Repeats

18. Termination
Stop codon sequence signifies the end of a polypeptide chain
tRNA enters A site, but doesn’t carry amino acid
Polypeptide released from P site tRNA
Ribosome splits
Polypeptide assumes level of structure (1° to 4°)

19. Mutations Changes to the genetic information of a cell
Ultimate source of diversity because ultimate source of new genes
Point mutation
Replace 1 nucleotide with another
Effect depends on codon
Base insertions and deletions
Changes reading frame
Most often deleterious effects
E.g. The cat ate the rat.