1 Genes and Proteins The genetic information contained in the nucleotide sequence of DNA specifies a particular type of protein Enzymes = proteins that are biological catalysts essential for metabolic activities in the cell Metabolites = small molecules upon which enzymes act In 1908 Archibald Garrod proposed that enzyme defects result in inborn errors of metabolism = hereditary diseases

2 Genes and Proteins Garrod studied alkaptonuria and identified abnormal excreted substance = homogentisic acid

3 Genes and Proteins Another defective enzyme in the same pathway, phenylalanine hydroxylase (PAH), leads to phenylalanine accumulation which causes the condition known as phenylketonuria (PKU) Incidence of PKU, characterized by severe mental retardation, is about one in 8000 among Caucasian births. A defective enzyme results from a mutant gene

4 Central Dogma Central Dogma of molecular genetics: DNA  RNA  Protein DNA is the informational molecule which does not code for protein directly but rather acts through RNA intermediate DNA codes for RNA = transcription RNA codes for protein = translation

5 Fig. 1.14

6 Transcription Transcription is the production of an RNA strand that is complementary in base sequence to a DNA template = messenger RNA (mRNA) RNA contains the base uracil in place of thymine and the sugar ribose instead of deoxyribose RNA is synthesized from template DNA following strand separation of the double helix Fig. 1.15

7 Base pairing in DNA and RNA Complementary base pairing specifies the linear sequence of bases in RNA Adenine pairs with uracil; thymine pairs with adenine; guanine pairs with cytosine

8 Translation The sequence of bases in mRNA codes for the sequence of amino acids in a polypeptide The mRNA is translated in nonoverlapping group of three bases = codons that specify the sequence of amino acids in proteins Each codon specifies one amino acid Transfer RNAs (tRNA) contain triplet base sequences = anticodons, which are complementary to codons in mRNA

9 Fig. 1.16

10 Translation Translation occurs at the ribosomes which contain several types of ribosomal RNA (rRNA) tRNAs participate in translation by carrying amino acids and positioning them on ribosomes Translation results in the synthesis of a polypeptide chain composed of a linear sequence of amino acids whose order is specified by the sequence of codons in mRNA

11 Mutations Mutation refers to any heritable change in a gene The change may be: substitution of one base pair in DNA for a different base pair; deletion or addition of base pairs Any mutation that causes the insertion of an incorrect amino acid in a protein can impair its function

12 Genes and Environment One gene can affect more than one trait = pleiotropy Any trait can be affected by more than one gene as well as environment Most complex traits are affected by multiple genetic and environmental factors Often several genes are involved in genetic disorders and the severity of a disease may depend upon genetic status and environmental factors

13 Evolution All creatures on Earth share many features of the genetic apparatus and many aspects of metabolism Groups of related organisms descend from a common ancestor Evolution occurs whenever a population of organisms with a common ancestry gradually changes in genetic composition over time

14 Fig. 1.21

15 Evolution The totality of DNA in a single cell = genome The complete set of proteins encoded in the genome = proteome Genes or proteins that derive from a common ancestral sequence via gene duplication = paralogs Genes that share a common ancestral gene via speciation = orthologs The molecular unity of life is seen in comparisons among genomes and proteomes

Self Assessment Questions: Question 1 The base thymine is always paired with: Adenine Thymine Guanine Cytosine Thymine is never paired with another base in a DNA molecule

Self Assessment Questions: Question 1 Answer The base thymine is always paired with: Adenine CORRECT ANSWER Thymine Guanine Cytosine Thymine is never paired with another base in a DNA molecule

The bases are projected inward whereas the sugar phosphate backbone is on the outside The two strands are antiparallel A is paired with T through two hydrogen bonds G is paired with C through three hydrogen bonds DNA forms a Double Helix

Self Assessment Questions: Question 2 The base cytosine is always paired with: Adenine Guanine Cytosine Thymine Cytosine is never paired with another base in a DNA molecule

Self Assessment Questions: Question 2 Answer The base cytosine is always paired with: Adenine Guanine CORRECT ANSWER Cytosine Thymine Cytosine is never paired with another base in a DNA molecule

Self Assessment Questions: Question 3 Which of the following is not a base found in DNA? Guanine Cytosine Thymine Uracil Adenine

Self Assessment Questions: Question 3 Answer Which of the following is not a base found in DNA? Guanine Cytosine Thymine Uracil CORRECT ANSWER Adenine

RNA contains the base uracil in place of thymine.

Self Assessment Questions: Question 4 Chromosomes can be found in the: Cytoplasm Endoplasmic reticulum Nucleus Cellular membranes

Self Assessment Questions: Question 4 Answer Chromosomes can be found in the: Cytoplasm Endoplasmic reticulum Nucleus CORRECT ANSWER Cellular membranes

Self Assessment Questions: Question 5 tRNA is: The major structural material making up ribosomes The molecule that carries the genetic information from DNA and is used as a template for protein synthesis The major structural component of chromosomes A molecule that incorporates a specific amino acid into the growing protein when it recognizes a specific group of three bases The major building block of proteins

Self Assessment Questions: Question 5 Answer tRNA is: The major structural material making up ribosomes The molecule that carries the genetic information from DNA and is used as a template for protein synthesis The major structural component of chromosomes A molecule that incorporates a specific amino acid into the growing protein when it recognizes a specific group of three bases CORRECT ANSWER The major building block of proteins

Four Basic Molecular Genetic Process: (1) Transcription, (2) RNA processing, (3) mRNA translation, (4) DNA replication

Self Assessment Questions: Question 6 rRNA is: The major structural material making up ribosomes The molecule that carries the genetic information from DNA and is used as a template for protein synthesis The major structural component of chromosomes A molecule that incorporates a specific amino acid into the growing protein when it recognizes a specific group of three bases The major building block of proteins

Self Assessment Questions: Question 6 Answer rRNA is: The major structural material making up ribosomes CORRECT ANSWER The molecule that carries the genetic information from DNA and is used as a template for protein synthesis The major structural component of chromosomes A molecule that incorporates a specific amino acid into the growing protein when it recognizes a specific group of three bases The major building block of proteins

Self Assessment Questions: Question 7 mRNA is: The major structural material making up ribosomes The molecule that carries the genetic information from DNA and is used as a template for protein synthesis The major structural component of chromosomes A molecule that incorporates a specific amino acid into the growing protein when it recognizes a specific group of three bases The major building block of proteins

Self Assessment Questions: Question 7 Answer mRNA is: The major structural material making up ribosomes The molecule that carries the genetic information from DNA and is used as a template for protein synthesis Correct Answer The major structural component of chromosomes A molecule that incorporates a specific amino acid into the growing protein when it recognizes a specific group of three bases The major building block of proteins

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