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
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
What Is a Protein?
Provide structure
Be enzymes
Be chemical messengers
Act as receptors
Be carrier molecules
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
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
5.2 What Happens in Transcription?
First step of information transfer
Information in DNA sequence gene is copied into sequence of bases in mRNA
p. 88
RNA polymerase DNA to be transcribed Initiation
1
Promoter Terminator
Elongation2
mRNA transcriptTermination
3
mRNA
4
RNA polymerase
Completed pre-mRNA
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
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
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
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
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
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
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
Mutagens
Increase chance of mutation
Mistakes during DNA replication
By-product of normal cell functions
Include:• Environmental factors• Radiation • Chemicals
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
Disorders from Altered 3-D Shape
Cystic fibrosis
Form of Alzheimer disease
Mad cow disease
Cruzfelt-Jacob disease (CJD)
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
Fig. 5-9, p. 93
Valine Histidine Leucine Threonine Proline Glutamic acid
Glutamate
Valine Histidine Leucine Threonine Proline Valine Glutamate