1. Genes as DNA: How Genes Encode Proteins
Chapter 5

2. Central Points Genes made of DNA that encodes proteins
Transcription: DNA copied into mRNA
Translation: information transferred to protein
Mutations: changes in DNA
Changes in DNA produce changes in proteins

3. 5.1 How Do Genes Control Traits?
Individuals carry two copies of each gene
One from each parent
Different forms are alleles
Genes contain information to produce proteins
Proteins contribute to the observable traits or phenotype

4. What Is a Protein? Provide structure Be enzymes Be chemical messengers
Act as receptors
Be carrier molecules

5. Protein Subunits: Amino Acids
20 found in the body
amino acids have different chemical groups
All contain both a carboxyl group and an amino group
Billions of combinations possible

6. Chemical Structure of Amino Acids

7. Essential Amino Acids

8. Amino acids Figure 5.3: Linked Amino Acids.
Amino acids linked together form a protein.
Amino acids
Fig. 5-3, p. 86

9. How Does DNA Carry Information?
DNA carries four nucleotides: A, T, G, and C
Three nucleotide codon in messenger RNA (mRNA) specifies one amino acid
Order of DNA bases determine the order of amino acids but not all DNA codes for proteins

10. Gene to Protein
Transcription: DNA  mRNA
Translation: mRNA Protein

11. Animation: Overview of transcription

12. 5.2 What Happens in Transcription?
First step of information transfer
Information in DNA sequence gene is copied into sequence of bases in mRNA

13. RNA polymerase DNA to be transcribed Initiation 1 Promoter Terminator
Elongation 2
mRNA transcript
Termination 3
mRNA 4
RNA polymerase
Completed pre-mRNA
p. 88

14. Transcription
RNA polymerase binds to promoter, DNA is template to produce mRNA
mRNA is a complementary copy of DNA
Bases pair, except T, is replaced by U
End of the gene, marked termination sequence
mRNA processed before leaving nucleus

15. Animation: From DNA to proteins (gene transcription)

16. 5.3 What Happens in Translation?
Second step, processed mRNA to the ribosome
Protein produced from information on mRNA
Each mRNA codon codes for an AA
Transfer RNA (tRNA) acts as an adaptor

17. Transfer RNA Recognizes and binds to one amino acid
Recognizes the mRNA codon for that amino acid
At one end binds a specific amino acid
Other end has a 3 nucleotide anticodon that pairs with mRNA codon for specific amino acid

18. Ribosome
mRNA
tRNA
Growing protein
p. 88

19. Translation (1) Synthesis of protein from mRNA Occurs within ribosomes
AUG (start codon) encodes for methionine
Second AA is in position, an enzyme forms a peptide bond between the two AA
tRNA for the first AA is released

20. Translation (2)
Ribosome to next codon and repeats adding AA to growing AA chain
Stop codons (UAA, UAG, and UGA) do not code for AA and ribosome detaches from mRNA
AA chain released, folds into a 3-D protein

21. TRANSCRIPTION DNA tRNA mRNA tRNA rRNA Nucleus Cytoplasm mRNA Ribosomes
TRANSLATION
Protein
p. 89

22. Animation: The 4 steps of translation

23. Genetic Code for Amino Acids

24. 5.4 Turning Genes On and Off
Only 5–10% genes active
Gene regulation turns genes on and off
Promoter controls expression
Also, cells receive signals
Enhancers increase protein production

25. Controlling Gene Expression

26. 5.5 Mutations Changes in DNA Produce:
Nonfunctional protein
Partially functional protein
No protein
Affect the timing and level of gene expression
Some no change

27. Mutagens Increase chance of mutation Mistakes during DNA replication
By-product of normal cell functions
Include:
Environmental factors
Radiation
Chemicals

28. Animation: Mutations and translation

29. Animation: From DNA to proteins (base substitution)

30. 5.6 Cause of Genetic Disorders
Change in DNA alters mRNA
Single nucleotide change can alter codon and possibly amino acid
Change in amino acid sequence causes changes in
3-D structure of protein
Defective protein folding
Protein function

31. Genetic Code

32. Disorders from Altered 3-D Shape
Cystic fibrosis
Form of Alzheimer disease
Mad cow disease
Cruzfelt-Jacob disease (CJD)

33. Sickle Cell Anemia Mutation in the hemoglobin gene
Hemoglobin (HbA) is composed of two proteins:
Alpha globin
Beta globin
Single nucleotide point mutation alters one of 146 AA, affects the beta globin
Causes hemoglobin molecules to stick together

34. Hemoglobin Molecule

35. Red Blood Cells

36. Point Mutation in Sickle Cell Anemia

37. Valine Histidine Leucine Threonine Proline Glutamic acid Glutamate
Figure 5.9: Amino Acid Chains for Hemoglobin Molecules.
The top sequence shows part of the amino acid chain for normal hemoglobin. Below it is the same sequence for a person with sickle cell anemia.
Valine
Histidine
Leucine
Threonine
Proline
Valine
Glutamate
Fig. 5-9, p. 93

38. 5.7 Other Single-Gene Defects
Cystic fibrosis (CF)
Misfolded protein
Protein destroyed
Huntington disease (HD)
Trinucleotide repeats
Multiple CAG repeats