Unit 2: Membranes, Energy, and Cell Communication

Membranes

Structure of Membranes

Phosplipid Bilayer

Phospholipids

Hydrophobic Tails (fatty acids)

Hydrophilic Head (phosphate group)

Maintains Flexibility

Glycoproteins

Cell-cell recognition & signal reception

Glycolipids

Cell recognition, stability & protection

Functions of membranes

Selective Permeability

Signal Transduction

Factors Affecting Fluidity

Cholesterol (maintains fluidity at various temperatures)

Temperature (higher = more fluid)

Fatty Acid Composition (unsaturated vs saturated)

Cell Energy

Energy Transfer in Cells

Cellular Respiration: ATP Production

Stages of Cellular Respiration

Glycolysis (Cytoplasm)

Outputs: Pyruvate, ATP (net 2), NADH

Inputs: Glucose, ATP, NAD+

Pyruvate Oxidation (Mitochondrial Matrix)

Outputs: Acetyl-CoA, NADH, CO₂

Inputs: Pyruvate, NAD+

Citric Acid Cycle (Krebs Cycle) (Mitochondrial Matrix)

Inputs: Acetyl-CoA, NAD+, FAD

Outputs: ATP, NADH, FADH₂, CO₂

Oxidative Phosphorylation (ETC + Chemiosmosis) (Inner Mitochondrial Membrane)

Inputs: NADH, FADH₂, O₂

Outputs: ATP (32-34), H₂O

Electron Transport Chain (ETC) & Chemiosmosis

Proton (H⁺) gradient in the intermembrane space drives ATP Synthase.

ATP is generated by oxidative phosphorylation.

Photosynthesis: ATP & Energy Transfer

Light-Dependent Reactions (Thylakoid Membrane)

Electron transport & proton pumping to create ATP and NADPH.

Calvin Cycle (Stroma)

ATP & NADPH used to fix CO₂ into glucose.

Comparison to Cellular Respiration

Both processes use electron transport chains.

ATP is generated using a proton gradient in both mitochondria and chloroplasts.

ATP: The Energy Currency

ATP Hydrolysis: ATP → ADP + Pᵢ (Releases energy)

ATP Synthesis: ADP + Pᵢ → ATP (Requires energy)

ATP used in:

Mechanical Work (Motor Proteins)

Transport Work (Active Transport)

Chemical Work (Biosynthesis)

Cell Signaling

GCPR receptor

Pathway

Ligand binds to GCPR receptor

GPT --> GTP and activates G protein

Activated G protein activates adenylyl cyclase

Adynylyl cyclase converts ATP --> cAMP

cAMP activates first kinase

Tyrosine Kinase receptor pathway

Ligand binds to dimer

activates kinase --> autophosphorylation of tyrosine

Phosphorylated tyrosines --> signaling proteins

activated signaling proteins --> cascades --> gene expression

ATP production in aerobic respiration

Glycolysis

ATP generation: 2 ATP made thourgh substrate level phosphorylation

ATP usage: 2 ATP consumed in first 5 steps of glycolysis

Citric acid cycle

ATP generation: 2 ATP made through substrate level phosphorylation

ETC

NADH and FADH2 made from glycolysis and citirc acid cycle, give e- to ETC

e- go through protein complexes

H+ pumped into intermembrane space, creates proton gradient

O2 combines with e- and protons to form water

Chemiosmosis

proton gradient drives ATP synthase, ADP + Pi --> ATP

Lots of ATP produced

ETC

location: inner membrane space

ATP production: chemiosmosis through ATP synthase

e-: from NADH and FADH2, gives to O2

Light reactions in photosynthesis

location: thylakoid membrane of chloroplast

e-: from H20, gives to NADP+

ATP production: chemiosmosis (protons pumped across thylakoid membrane, create sproteon gradient, drives ATP synthase)

Transport across Membranes

No ATP Required

Diffusion

Facilitated Diffusion

Osmosis

Co-transport

ATP Required

Active Transport

Endocytosis & Exocytosis

Subtopic

Peripheral Proteins

Hydrophilic R groups

Integral Proteins

Hydrophobic R groups

Channel Protein

Carrier Protein

Active Transport Pumps

Cotransport Proteins