Evolution, Proteins, Enzymes, & DNA: General Biology Study Notes

Evolution

Concept of Evolution

Evolution refers to the diversity of life that has evolved over time through processes such as mutation, selection, and genetic change. It is the cumulative change in heritable characteristics of a population over generations.

• Mutation: Random changes in DNA sequence that introduce genetic variation.

• Selection: Differential survival and reproduction of individuals based on inherited traits.

• Genetic Change: Changes in allele frequencies within a population over time.

Species and Population

A species is a group of related organisms that share distinctive traits and can interbreed to produce viable, fertile offspring. A population consists of members of the same species likely to interbreed.

• Gene Pool: The total genetic information available in a population.

Evolutionary Change

Evolutionary change is measured by changes in allele frequency in a population over time. This cumulative change in genetic traits is the basis for adaptation and speciation.

• Adaptation: Traits that enhance survival and reproduction in a specific environment.

Mutations

Mutations are changes in the DNA sequence that can occur randomly anywhere in the genome. They are the source of genetic variation, which is essential for evolution.

• Germline Mutations: Occur in reproductive cells and are heritable.

• Somatic Mutations: Occur in body cells and are not passed to offspring.

Mechanisms of Evolution

Natural selection, genetic drift, gene flow, and mutation are the main mechanisms driving evolution.

• Natural Selection: Differential survival and reproduction based on trait advantages.

• Genetic Drift: Random changes in allele frequencies, especially in small populations (e.g., bottleneck effect).

• Gene Flow: Migration of alleles between populations.

Evolutionary Fitness

Fitness is the ability of an organism to survive and reproduce, passing its genes to the next generation.

• Relative Fitness: Comparison of reproductive success among individuals.

Adaptation and Natural Selection

Adaptation is the result of natural selection acting on heritable variation, leading to traits that increase survival and reproductive success.

• Example: The development of antibiotic resistance in bacteria.

Proteins

Structure of Proteins

Proteins are polymers of amino acids linked by peptide bonds. Their structure determines their function in biological systems.

• Polypeptide: Linear polymer of amino acids.

• Macromolecules: Large molecules such as proteins, nucleic acids, and polysaccharides.

• Protein Assembly: Proteins are assembled from amino acids via translation of mRNA.

Amino Acids

Amino acids are the building blocks of proteins, each with a central carbon, amino group, carboxyl group, and a unique side chain (R group).

• Types of R Groups: Nonpolar, polar, acidic, and basic.

• Peptide Bond: Covalent bond between the carboxyl group of one amino acid and the amino group of another.

Protein Structure Levels

Proteins have four levels of structure:

• Primary Structure: Sequence of amino acids.

• Secondary Structure: Local folding into alpha helices and beta sheets, stabilized by hydrogen bonds.

• Tertiary Structure: Overall 3D shape formed by interactions among R groups.

• Quaternary Structure: Association of multiple polypeptide chains.

Protein Folding and Function

Protein folding is essential for function. Misfolded proteins can lead to diseases. Protein function is determined by its structure and interactions with other molecules.

• Enzymes: Proteins that catalyze biochemical reactions.

• Transport Proteins: Move substances across membranes.

• Structural Proteins: Provide support and shape to cells and tissues.

Protein Visualization Methods

Proteins can be visualized and analyzed using techniques such as X-ray crystallography, NMR, and SDS-PAGE.

• SDS-PAGE: Separates proteins based on size.

• X-ray Crystallography: Determines 3D structure.

Enzymes

Enzyme Structure and Function

Enzymes are dynamic proteins that catalyze chemical reactions by lowering activation energy. They have specific active sites where substrates bind.

• Active Site: Region on the enzyme where substrate binds and reaction occurs.

• Induced Fit Model: Enzyme changes shape to better fit the substrate.

Enzyme Kinetics

Enzyme kinetics studies the rates of enzyme-catalyzed reactions and how they are affected by factors such as temperature, pH, and substrate concentration.

• Activation Energy ($E_a$): Minimum energy required for a reaction to occur.

• Free Energy Change ($\Delta G$): Determines whether a reaction is spontaneous.

• Spontaneous Reaction: $\Delta G < 0$

• Nonspontaneous Reaction: $\Delta G > 0$

Enzyme Regulation

Enzymes can be regulated by inhibitors, activators, and covalent modifications.

• Competitive Inhibition: Inhibitor competes with substrate for active site.

• Allosteric Regulation: Molecule binds at a site other than the active site, changing enzyme activity.

DNA

Structure of DNA

DNA (deoxyribonucleic acid) is the hereditary material in all living organisms. It consists of two antiparallel strands forming a double helix.

• Nucleotides: Building blocks of DNA, each composed of a phosphate group, deoxyribose sugar, and nitrogenous base (adenine, thymine, cytosine, guanine).

• Base Pairing: Adenine pairs with thymine, cytosine pairs with guanine.

• Double Helix: Two strands held together by hydrogen bonds between complementary bases.

DNA Replication

DNA replication is the process by which DNA makes a copy of itself during cell division. It is semi-conservative, meaning each new DNA molecule contains one old and one new strand.

• Enzymes Involved: DNA polymerase, helicase, primase, ligase.

• Replication Fork: Y-shaped region where DNA is unwound and replicated.

Genetic Information and Expression

DNA stores genetic information that is transcribed into RNA and translated into proteins.

• Transcription: Synthesis of RNA from DNA template.

• Translation: Synthesis of protein from mRNA template.

Mutations in DNA

Mutations in DNA can lead to changes in protein structure and function, potentially causing genetic disorders or contributing to evolution.

• Point Mutation: Change in a single nucleotide.

• Frameshift Mutation: Insertion or deletion of nucleotides that alters the reading frame.

Table: Types of Amino Acid R Groups

Type	Properties	Examples
Nonpolar	Hydrophobic, often found in interior of proteins	Leucine, Valine
Polar	Hydrophilic, can form hydrogen bonds	Serine, Threonine
Acidic	Negatively charged at physiological pH	Aspartic acid, Glutamic acid
Basic	Positively charged at physiological pH	Lysine, Arginine

Table: DNA vs. RNA

Feature	DNA	RNA
Sugar	Deoxyribose	Ribose
Bases	A, T, C, G	A, U, C, G
Strands	Double	Single
Function	Genetic information storage	Protein synthesis, gene regulation

Additional info: Some explanations and examples have been expanded for clarity and completeness based on standard General Biology curriculum.