Genetics and Evolution- Molecular Basis of Inheritance

Types of Amino Acids

• Amino acids are the building blocks of proteins
• There are 20 different types of amino acids
• Each amino acid is composed of an amino group, a carboxyl group, and a unique side chain
• Side chain determines the characteristics and properties of the amino acid
• Amino acids are classified into five different groups based on the properties of their side chains:

1. Non-polar amino acids

2. Polar amino acids

3. Acidic amino acids

4. Basic amino acids

5. Aromatic amino acids

Non-polar Amino Acids

• Non-polar amino acids have hydrophobic side chains
• They avoid water and tend to be found in the interior of proteins
• Examples of non-polar amino acids include:

1. Glycine (Gly)

2. Alanine (Ala)

3. Valine (Val)

4. Leucine (Leu)

5. Isoleucine (Ile)

6. Methionine (Met)

7. Proline (Pro)

Polar Amino Acids

• Polar amino acids have hydrophilic side chains
• They interact with water and can be found on the surface of proteins
• Examples of polar amino acids include:

1. Serine (Ser)

2. Threonine (Thr)

3. Cysteine (Cys)

4. Asparagine (Asn)

5. Glutamine (Gln)

Acidic Amino Acids

• Acidic amino acids have negatively charged side chains
• They are often involved in protein-protein interactions and enzymatic reactions
• Examples of acidic amino acids include:

1. Aspartic acid (Asp)

2. Glutamic acid (Glu)

Basic Amino Acids

• Basic amino acids have positively charged side chains
• They are often involved in DNA binding and enzyme catalysis
• Examples of basic amino acids include:

1. Lysine (Lys)

2. Arginine (Arg)

3. Histidine (His)

Aromatic Amino Acids

• Aromatic amino acids have a ring structure in their side chains
• They are often involved in protein structure and function
• Examples of aromatic amino acids include:

1. Phenylalanine (Phe)

2. Tyrosine (Tyr)

3. Tryptophan (Trp)

Summary

• Amino acids are the building blocks of proteins
• There are 20 different types of amino acids
• Amino acids are classified into five groups based on the properties of their side chains
• Non-polar amino acids have hydrophobic side chains
• Polar amino acids have hydrophilic side chains
• Acidic amino acids have negatively charged side chains
• Basic amino acids have positively charged side chains
• Aromatic amino acids have a ring structure in their side chains

11. Non-polar Amino Acids

• Non-polar amino acids have hydrophobic side chains.
• They avoid water and tend to be found in the interior of proteins.
• Glycine (Gly): Smallest and most flexible amino acid.
• Alanine (Ala): Simplest non-polar amino acid.
• Valine (Val): Branch-chained amino acid.
• Leucine (Leu): Aliphatic amino acid.
• Isoleucine (Ile): Aliphatic amino acid with a branched side chain.
• Methionine (Met): Contains sulfur in the side chain.
• Proline (Pro): Unique structure with a cyclic side chain.

12. Polar Amino Acids

• Polar amino acids have hydrophilic side chains.
• They interact with water and can be found on the surface of proteins.
• Serine (Ser): Contains a hydroxyl group in the side chain.
• Threonine (Thr): Contains a hydroxyl group and a methyl group in the side chain.
• Cysteine (Cys): Contains a sulfhydryl group, involved in disulfide bond formation.
• Asparagine (Asn): Contains an amide group in the side chain.
• Glutamine (Gln): Contains a primary amide group in the side chain.

13. Acidic Amino Acids

• Acidic amino acids have negatively charged side chains.
• They are often involved in protein-protein interactions and enzymatic reactions.
• Aspartic acid (Asp): Contains a carboxyl group in the side chain.
• Glutamic acid (Glu): Contains a longer carboxyl group in the side chain.
• Example: Aspartic acid is involved in the catalytic activity of the enzyme aspartate transcarbamoylase.

14. Basic Amino Acids

• Basic amino acids have positively charged side chains.
• They are often involved in DNA binding and enzyme catalysis.
• Lysine (Lys): Contains an amino group in the side chain.
• Arginine (Arg): Contains a guanidino group in the side chain.
• Histidine (His): Contains an imidazole group in the side chain.
• Example: Histidine is often involved in the active sites of enzymes due to its ability to donate and accept protons.

15. Aromatic Amino Acids

• Aromatic amino acids have a ring structure in their side chains.
• They are often involved in protein structure and function.
• Phenylalanine (Phe): Contains a benzyl ring in the side chain.
• Tyrosine (Tyr): Contains a hydroxylated benzyl side chain.
• Tryptophan (Trp): Contains an indole ring in the side chain.
• Example: Tryptophan is often found in the hydrophobic core of proteins and can participate in protein-ligand interactions.

16. Summary

• Amino acids are the building blocks of proteins.
• There are 20 different types of amino acids.
• Non-polar amino acids have hydrophobic side chains.
• Polar amino acids have hydrophilic side chains.
• Acidic amino acids have negatively charged side chains.
• Basic amino acids have positively charged side chains.
• Aromatic amino acids have a ring structure in their side chains.

17. Importance of Amino Acids in Protein Structure and Function

• Amino acids are essential for the structure and function of proteins.
• The sequence of amino acids determines the primary structure of a protein.
• The specific arrangement of amino acids leads to the formation of secondary structures like alpha helices and beta sheets.
• The overall 3D structure of a protein, called the tertiary structure, is determined by the interactions between amino acids.
• Amino acids play a crucial role in protein-ligand interactions and enzymatic reactions.

18. Mutations in Amino Acid Sequences

• A mutation is a change in the DNA sequence, which can result in a change in the amino acid sequence of a protein.
• Missense mutation: A single nucleotide change leading to the substitution of one amino acid for another.
• Nonsense mutation: A single nucleotide change leading to the introduction of a premature stop codon, resulting in a truncated protein.
• Frameshift mutation: Insertion or deletion of nucleotides, leading to a shift in the reading frame, affecting the entire amino acid sequence downstream.
• Mutations in the amino acid sequence can alter the protein structure and function, leading to diseases or altered phenotypes.

19. Genetic Code and Amino Acid Synthesis

• Genetic code: Set of rules that define how DNA sequences are translated into amino acid sequences
• The genetic code is degenerate, meaning multiple codons can code for the same amino acid.
• Transfer RNA (tRNA) molecules bring the correct amino acids to the ribosome during translation.
• Amino acid synthesis: Cells can synthesize certain amino acids using specific metabolic pathways.
• Essential amino acids: Humans must obtain some amino acids from the diet, as they cannot be synthesized in the body.

20. Applications of Amino Acids

• Amino acids have various applications in biology and beyond.
• Protein engineering: Amino acids can be modified or replaced to improve protein stability, function, or specificity.
• Peptide synthesis: Amino acids are used to synthesize peptides and small proteins for research or medical applications.
• Amino acid supplements: Amino acid supplements are used by athletes to enhance muscle growth and recovery.
• Amino acids can be used to produce antibiotics, pigments, and other biotechnological products.

21. Gene Expression and Protein Synthesis

• Gene expression is the process by which information from a gene is used to synthesize a functional protein.
• It involves two main steps: transcription and translation.
• Transcription occurs in the nucleus, where the DNA sequence of a gene is copied into a molecule called messenger RNA (mRNA).
• Translation occurs in the cytoplasm, where the mRNA is used as a template to synthesize a specific protein.
• During translation, the sequence of codons in the mRNA is decoded by ribosomes, and corresponding amino acids are added to the growing protein chain.

22. Transcription: From DNA to mRNA

• Transcription is the process of synthesizing mRNA from a DNA template.
• It is carried out by an enzyme called RNA polymerase.
• The DNA molecule unwinds, and one of the DNA strands serves as a template for RNA synthesis.
• RNA polymerase adds complementary RNA nucleotides to the growing mRNA strand, following base-pairing rules.
• The mRNA molecule is synthesized in the 5’ to 3’ direction.

23. Genetic Code and Codons

• The genetic code consists of a specific sequence of three nucleotides called a codon.
• Each codon codes for a specific amino acid or a stop signal.
• There are 64 possible codons, but only 20 amino acids, so the code is degenerate.
• Example: AUG is the start codon that codes for methionine, and UAA, UAG, and UGA are stop codons.

24. Translation: From mRNA to Protein

• Translation is the process of synthesizing a protein using the information encoded in mRNA.
• It occurs at ribosomes in the cytoplasm.
• Transfer RNA (tRNA) molecules bring specific amino acids to the ribosome, guided by the codon-anticodon interaction.
• Amino acids are added to the growing polypeptide chain in a specific order according to the sequence of codons in the mRNA.
• The process continues until a stop codon is reached, and the protein is released.

25. Post-Translational Modifications

• After translation, proteins undergo various modifications to become functional.
• Some common post-translational modifications include:
  1. Folding and shaping: Proteins adopt their proper 3D structure.
  2. Cleavage: Unwanted segments of the protein are removed.
  3. Addition of functional groups: Phosphorylation, acetylation, or glycosylation can alter protein function.
  4. Assembly into complexes: Proteins may join together to form larger functional units.
  5. Targeting to specific locations: Proteins can be directed to specific cellular compartments.

26. Mutations in the Genetic Code

• Mutations are changes in the DNA sequence that can alter the genetic code.
• Point mutations: Single nucleotide changes, including substitutions, insertions, and deletions.
• Frameshift mutations: Insertions or deletions of nucleotides that disrupt the reading frame of the genetic code.
• Silent mutations: DNA changes that don’t alter the amino acid sequence due to the degeneracy of the genetic code.
• Missense mutations: DNA changes that result in the incorporation of a different amino acid into the protein.
• Nonsense mutations: DNA changes that introduce a premature stop codon, leading to the production of a truncated protein.

27. Effects of Mutations on Proteins

• Mutations in the genetic code can have various effects on protein structure and function.
• Some mutations disrupt the protein structure and render it non-functional.
• Other mutations can lead to gain or loss of protein function.
• Some mutations may not have any noticeable effect on the protein.
• Mutations can also contribute to the development of genetic disorders and diseases.

28. Inheritance of Mutations

• Mutations can be inherited from parents or arise spontaneously in an individual’s genome.
• Germ line mutations occur in the reproductive cells and can be passed on to offspring.
• Somatic mutations occur in non-reproductive cells and are not passed on to offspring.
• Some mutations can be beneficial, harmful, or have no effect on an organism’s fitness.
• The inheritance pattern of a mutation depends on the type of mutation and the affected genes.

29. Applications of Genetic Engineering

• Genetic engineering involves manipulating the genetic material of organisms to produce specific traits.
• It has various applications in areas such as agriculture, medicine, and industry.
• Examples of genetic engineering applications include:
  1. Crop improvement: Genetically modified crops with enhanced traits, such as pest resistance and improved nutritional content.
  2. Gene therapy: Correcting genetic disorders in humans by introducing functional genes or modifying existing ones.
  3. Production of recombinant proteins: Using genetically modified organisms to produce valuable proteins, such as insulin or vaccines.
  4. Environmental cleanup: Genetically engineered microorganisms can help degrade pollutants and clean up contaminated sites.

30. Ethical Considerations in Genetic Engineering

• Genetic engineering raises ethical issues and concerns that must be addressed.
• Some key ethical considerations include:
  1. Safety: Ensuring the safety of genetically modified organisms and their impact on the environment.
  2. Justice and equity: Considering the distribution and accessibility of genetically modified products.
  3. Informed consent: Respecting individuals’ rights to knowledge and consent regarding genetic testing and therapies.
  4. Playing God: Debating the moral implications of manipulating the genetic code and altering the course of evolution.
  5. Long-term effects: Assessing the potential long-term consequences of genetic engineering on ecosystems and species.