Metabolic Reactions Two major types: Anabolic: Def – buildup of larger molecules from smaller ones Requires energy Usually required for cell growth and repair Ex: Dehydration synthesis (building of macromolecules from monomers) Catabolic: Def – breakdown of larger molecules into smaller ones Releases energy Ex: Digestion, hydrolysis (breakdown of macromolecules)

Enzymes Def: complex molecules (almost always proteins) that speed up chemical reactions Lower activation energy (energy needed to get rxn started) Considered catalysts (speed up rxn) Not consumed during rxn (can be reused) Only needed in small amounts Very specific to a chemical reaction (or even sub-steps of a chemical rxn) Parts to a enzyme-catalyzed rxn: Substrate Active site

Enzymes Substrate: Def: chemical on which enzyme acts Target of an enzyme reaction Active site: Def: the part of the enzyme in which substrate binds Specific to each substrate Places strain on chemical bonds – which intensifies chemical reaction

Enzymes Environmental factors can effect enzymes: Temp: most enzymes become inactive at 45 o C (113 o F) Heat: enzymes may become denatured (change shape/function) with extreme heat Radiation: denaturizing UV: can destroy nucleic acids (and the enzymes working on them!) Chemicals/pH: specific environment must be controlled Cyanide and carbon monoxide: can destroy respiratory enzymes

Enzymes Some enzymes remain inactive until they bind with a nonprotein helper Two types: 1) Cofactor Ion of an element (copper, zinc, iron) 2) Coenzyme Small organic molecule (most are vitamins) Ex: coenzyme A (cellular respiration) Enzyme Intro movie Enzyme Intro movie

Energy for Metabolic Reactions Energy: capacity to do work (change or move matter) Common forms: heat, light, sound, electricity, mechanical, chemical Most metabolic reactions use chemical energy Chemical energy: energy held in the bonds between atoms of molecules Released when bonds are broken (usually starts when heat is applied)

Energy for Metabolic Reactions ATP: chief energy- storing molecule of cells Contains 3 phosphate groups Energy is released once a phosphate group is broken off (and become ADP)

Energy for Metabolic Reactions Cellular respiration: Process by which food molecules are broken down (using input of water), making energy (form of ATP) and carbon dioxide Cellular respiration steps (3): 1)Glycolysis: breaks down glucose, occurs in cytoplasm, forms pyruvate 2) Citric Acid/Krebs cycle: uses pyruvate to make energy- containing electron carrier compounds, occurs mitochondria 3) Electron transport chain: uses electron carrier compounds from step 2 to drive a series of reactions, creates a LOT of ATP energy, occurs in cristae of mitochon.

Energy for Metabolic Reactions Two types of cellular respiration: Aerobic: Uses oxygen Produces maximum amount of energy/ATP Also produces large amount of water Anaerobic: Without oxygen use Only goes through glycolysis Produces very little energy/ATP Will produce lactic acid or ethyl alcohol through fermentation reaction Lactic acid – causes muscle cramps in humans Ethyl alcohol – can be used to make alcoholic beverages

Metabolic Pathways Def: A sequence of enzyme-controlled reactions Ex: DNA replication, protein synthesis Rate often determined by regulatory enzyme Regulatory enzyme: an enzyme responsible by one or more steps of the pathway Present in limited quantity

DNA Replication DNA: Consists of nucleotide: Sugar, nitrogenous bases, phosphate groups Bases: adenine, thymine, cytosine, guanine Base pairs: A-T, C-G Double-stranded molecule made of nucleotides hydrogen bonded to each other DNA replication: Def: making copy of DNA molecule during S-phase of Interphase Mutations: changes in DNA sequence, often caused by issues during DNA replication

DNA Replication Steps of replicationSteps of replication: 1) Hydrogen bonds break between base pairs (which connect strands) 2) DNA pulls apart and unwinds (by an enzyme called helicase) 3) Nucleotides are exposed 4) DNA polymerase (enzyme) brings in free nucleotides to pair up with existing nucleotides 5) Sugar/Phosphate backbone is put together (by another class of enzymes) 6) DNA proofread for errors (by special class of enzymes) 7) DNA winds back up

Protein Synthesis Cells synthesize/build proteins by using genetic code (DNA sequence) DNA sequence codes for amino acids (which combine to form proteins) Uses DNA, RNA RNA: ribonucleic acid Single-stranded 3 types: m, r, t Contains nucleotides Sugar (ribose), bases (A,U,C,G), phosphate U = uracil (nitrogenous base NOT found in DNA)

Protein Synthesis Steps: Transcription: Takes place in nucleus Make RNA (messenger RNA) by using DNA sequence as a template RNA processing: Occurs just after transcription (before 2 nd step) Involves adding nucleotides (or removing!) Help protect RNA from degradation Remove non-coding regions

Protein Synthesis Steps: Translation: Takes place on ribosomes (in cytoplasm) Makes amino acid sequences (polypeptides) Uses tRNA (transfer RNA), rRNA (ribosomal) and mRNA tRNA – transfers amino acid to growing chain by pairing up with mRNA bases (codons) rRNA – found in ribosome (location of translation) mRNA – made in transcription, used as a template, 3-base sections (called codons) pair up with 3-base sections (anticodons) on tRNA Animation