Molecular Biology and Linear Equations

Molecular Biology

Objectives

• Identify where hereditary information is stored in a cell: Hereditary information is stored in the nucleus of eukaryotic cells and in the nucleoid region of prokaryotic cells.

• Identify how hereditary information is stored in a molecule: Hereditary information is stored in the sequence of nucleotides in DNA.

Structure of DNA

• Definition: Deoxyribonucleic acid (DNA) is the hereditary material in living organisms.

• Monomer: The building block of DNA is the nucleotide.

• Components of a Nucleotide:

• Phosphate group: Links nucleotides together in the DNA strand.

• Deoxyribose sugar: Forms the backbone of DNA.

• Nitrogenous base: Can be adenine (A), thymine (T), cytosine (C), or guanine (G).

• Four Bases of DNA:

• Adenine (A): Pairs with thymine (T) in DNA.

• Thymine (T): Pairs with adenine (A).

• Cytosine (C): Pairs with guanine (G).

• Guanine (G): Pairs with cytosine (C).

• Complementary Strands: Base pairing (A-T, C-G) stabilizes the DNA structure. Given a strand of DNA, the complementary strand can be produced based on base pairing rules.

Making More DNA

Importance of DNA Replication

• DNA replication ensures genetic information is accurately copied and passed on to future generations. Each copy may be distributed to daughter cells during cell division, ensuring each cell receives full genetic instructions.

Major Enzymes in DNA Replication

• Helicase: Unwinds and separates the two strands of DNA at the replication fork.

• DNA Polymerase: Synthesizes new DNA strands and proofreads the sequence for accuracy.

• Ligase: Joins Okazaki fragments on the lagging strand and seals breaks in the sugar-phosphate backbone.

Leading vs. Lagging Strand

• Leading Strand: Synthesized continuously in the same direction as the replication fork.

• Lagging Strand: Synthesized in short segments (Okazaki fragments) in the opposite direction; requires additional processing.

• Semiconservative Replication: Each new DNA molecule consists of one original strand and one newly synthesized strand, preserving genetic information.

Cellular Respiration and Making ATP

Overview

• Function: Cellular respiration converts biochemical energy from nutrients into ATP, releasing byproducts such as CO2 and water.

• Overall Equation: [ C{6}H{12}O{6} + 6O{2} \rightarrow 6CO{2} + 6H{2}O + ATP ]

• Comparison with Photosynthesis: Photosynthesis stores energy in glucose from sunlight, while cellular respiration releases energy from glucose to produce ATP.

ATP Generation

• Two Ways:

• Substrate-level phosphorylation: Transfer of a phosphate group to ADP during glycolysis and the Krebs cycle.

• Oxidative phosphorylation: Occurs in the electron transport chain via redox reactions coupled with chemiosmosis.

Phases of Aerobic Cellular Respiration

• Three Phases:

1. Glycolysis: Occurs in the cytoplasm, the breakdown of glucose into two pyruvate, resulting in 2 ATP and 2 NADH.

2. Krebs Cycle: Occurs in the mitochondrial matrix, processes pyruvate, producing NADH, FADH2, ATP, and CO2 as a byproduct.

3. Electron Transport Chain: Located in the inner mitochondrial membrane, uses NADH and FADH2 to create a proton gradient for ATP synthesis.

Glycolysis

• Description: Breakdown of glucose into two pyruvate molecules, resulting in a net gain of 2 ATP and 2 NADH; anaerobic process.

• Products' Pathway: Depending on oxygen availability, pyruvate may enter the Krebs Cycle or undergo fermentation (producing lactic acid or ethanol) in anaerobic conditions.

Central Dogma

Protein Synthesis Steps

• Transcription: RNA synthesized from a DNA template, producing mRNA that carries genetic information to ribosomes.

• Translation: The ribosome reads the mRNA and produces a polypeptide chain using tRNA to bring in appropriate amino acids.

DNA vs. RNA

• DNA Structure: Double-stranded helix with a sugar-phosphate backbone, contains deoxyribose, and bases A, T, C, G.

• RNA Structure: Typically single-stranded, contains ribose, and bases A, U (replaces T), C, G, serving various roles in protein synthesis.

Genetic Code

• Codons: Sequences of three nucleotides corresponding to specific amino acids; examples include AUG (start codon) and UAA, UAG, UGA (stop codons).

Changing You

Mutations

• Definition: Permanent DNA sequence alterations caused by environmental factors or replication errors.

• Types of Mutagens: Physical agents (e.g., UV radiation), chemical agents (e.g., certain chemicals).

Types of Mutations

• Substitutions: A base replaced by another.

• Silent: No effect on protein product.

• Missense: Amino acid change affecting function.

• Nonsense: Premature stop codon leads to truncated protein.

• Insertions: Additional bases disrupt the reading frame, affecting the protein.

• Deletions: Bases removed, causing frame shifts and altering the protein.

Mutation Effects

• Silent Mutation: No change in protein function or expression.

• Missense Mutation: May cause diseases or variations based on amino acid change location.

• Nonsense Mutation: Often results in nonfunctional proteins, with severe consequences for the organism.