1. From Gene to Protein pp 344-361
Discover Biology: C15
From Gene to Protein pp

2. How Genes Work
DNA’s nucleotide sequence determines 1o structure of RNA & protein
DNA is transcribed into a messenger RNA (mRNA) copy
DNA encodes ribosomal RNA (rRNA)
DNA encodes transfer RNA (tRNA)
RNA directs synthesis of proteins
rRNA combines with cytoplasmic proteins to form ribosomes.
mRNA’s sequence, 3 bases/ codon, is translated into amino acids proteins
tRNA transports amino acids, specific to mRNA codon, to ribosomes
Proteins are multifunctional
Structure
Locomotion
Defense
Enzymes (Biological catalysts)

3. Genes Affecting Phenotype
1902: Archibald Garrod & William Bateson
Alkaptonuria caused by defective enzyme
Lack of proper enzyme causes urine to be black
Genes control production of enzymes
Major contribution by Garrod & Bateson
Noncoding genes
DNA codes for RNA
Protein-coding Genes
DNA codes for all proteins, including enzymes
Gene = any DNA transcribed into RNA

4. RNA versus DNA DNA = Deoxyribonucleic acid RNA = Ribonucleic acid
Double-stranded a-helix in nucleus only
Sugar (deoxyribose) – phosphate backbone
Nucleotides attached to 3’ or 5’ hydroxyl of sugar
Nucleotides hydrogen-bond to each other to join 2 strands
Adenine to Thymine (2 H-bonds)
Guanine to Cytosine (3 H-bonds)
RNA = Ribonucleic acid
Single-stranded; cytoplasmic
Sugar (ribose) – phosphate backbone
Nucleotides include Adenine, Guanine, Cytosine, & Uracil
Less stable than DNA; limited life in cytoplasm

5. DNA vs. RNA

6. From DNA to Protein

7. Transcription vs. Replication
Creates single-stranded mRNA via RNA polymerase
Only 1 strand of DNA, the template strand, is “read”
Only 1 section of DNA, the gene, is copied.
Prokaryotic transcription ceases at hairpin loops in mRNA/ DNA terminator
Replication
Creates 2 semi-conserved double-stranded copies of DNA
DNA polymerase binds promoter and reads/ writes/ checks DNA
Both the leading & lagging strands of DNA are copied
The entire chromosome is copied

8. Transcription DNA is unwound by helicase
Nuclear binding proteins stabilize DNA strands
RNA polymerase binds promoter on DNA template strand
RNA polymerase makes RNA copies of DNA’s nucleotide sequence
Polymerase adds base pairs complementary to DNA’s nucleotides
DNA’s adenine is matched with uracil, thymine with adenine, cytosine with guanine, & guanine to cytosine
Pre-mRNA is processed into mRNA
Nucleotides coding for introns are excised; exons are spliced together
Alternate splicing creates different arrangements of exons  new proteins
mRNA has additional nucleotides added as a “cap” and as a “poly-A tail”

9. Translation and the Genetic Code

10. Genetic Code Universal Unambiguous Redundant
All living creatures thus recognized have the same genetic code
Unambiguous
Each codon specifies 1 amino acid
There are 20 essential amino acids
Redundant
Several different codons may call for the same amino acid
There are 64 total codons (43 = 64)
Wobble effect: Sometimes the 3rd nucleotide is nonspecific for the amino acid

11. Translation: On the Ribosomes

12. tRNA

13. Genetic Mutations Point Mutation
A single nucleotide is changed
A different nucleotide is substituted = Substitution
Not all substitutions lead to phenotype mutations
Introns
Wobble effect in codons
A nucleotide is added = Insertion
A nucleotide is removed - Deletion
Insertion & Deletion mutations disrupt the original sequence
Frameshift mutations arise with insertions & deletions
Entirely new codon sequence is created; therefore, new amino acids linked.
More deleterious if mutation is near the front of the gene
Can create a stop codon & truncate the protein

14. Protein Structure Primary structure Secondary structure
Amino acid sequence
Secondary structure
Regional folding of amino acid chain
Alpha helix (spiral) & Beta sheets (ridges & valleys)
Tertiary structure
Interactions among distal segments
Ionic & covalent bonds (disulfide bonds between cysteines)
Quaternary structure
Between different polypeptides (e.g., hemoglobin)

15. Form Follows Function
If the structure is changed, so is the behavior of protein
Proteins/ enzymes depend on their 3-D shape to elicit effects
Denaturation
Typically permanent
High or low pH pH = - log [H+] = log 1 / [H+]
Extreme Temperatures
High Salinity