Lecture Notes Review: Cellular Energy, Cellular Respiration, and Plasma Membrane (Video)

Exam and Logistics

Exam #1: Tue September 9, 12:40 PM – 1:40 PM; 50 questions (multiple choice, True/False, matching); 1 hour to complete once started.
Focus on Learning Objectives (exclude sections 1.5 and 4.3).
Bring student ID and a pencil.
Practice Quiz #1 on D2L starts Friday morning.
Kahoot session: Monday September 8 at 6:00 PM online; will be recorded.
Kahoot and exam logistics are for preparation and assessment; emphasize learning objectives over memorization of slide details.

Learning Objectives

List five important molecules within the body that function primarily in chemical energy exchange and how long that energy source can sustain exercise.
Describe the four phases of cellular respiration including the reactants, products, and where in the cell the process occurs.
Explain what is meant by the term oxidative phosphorylation.

Energy Exchange Molecules and Their Energies

ATP as the primary immediate energy carrier; energy duration: extremely short-term fuel.
Phosphocreatine (PCr) as a rapid energy buffer; energy duration: brief, high-intensity efforts.
Glycogen as stored glucose; energy source for longer duration exercise.
Lipids as a large energy store, used during prolonged, lower-intensity exercise.
Proteins as a minor energy source under certain conditions (e.g., prolonged fasting or extreme exertion).
Key reaction schemas:
- ADP + Pi → ATP
  ext{ADP} + ext{P}_i
  ightarrow ext{ATP}
- ADP + PCr → Cr + ATP
  ext{ADP} + ext{PCr}
  ightarrow ext{Cr} + ext{ATP}
ATP and PCr concentrations in resting cells:
- ATP levels are maintained relatively constant by balanced production and use.
- PCr concentrations are 4–5 times higher than ATP levels.
Specific energy contributions and timings:
1) ATP: ~2 s of fuel or ~8 mM
ext{ATP} ext{ duration}
oughly 2 ext{ s} ext{ of fuel; concentration about } 8~ ext{mM}
2) PCr: ~10 s of fuel or ~40 mM
ext{PCr duration}
oughly 10 ext{ s}; [PCr]
oughly 40~ ext{mM}
3) Glycogen: stored glucose (liver and skeletal muscle) for extended exercise; can sustain for 1–2 hours; glycogen is the primary fuel for moderate-to-high intensity beyond the PCr stage.
- Glycogen is a stored polysaccharide of glucose units used for rapid glycolysis when needed.
Summary point: ATP and PCr provide rapid, high-intensity energy for very short durations; glycogen extends available energy; lipids and proteins become more important as exercise duration increases.
Important note on glycogen and glucose handling:
- Glycogen can be synthesized (anabolism) when energy is plentiful and glucose is abundant.
- Glycogen can be broken down to glucose (catabolism) during exercise to fuel metabolism.

Glycolysis and Cellular Respiration (Four Phases)

Four phases of cellular respiration:
1) Glycolysis (in the cytosol)
2) Intermediate Stage (pyruvate oxidation) (mitochondrial matrix)
3) Citric Acid Cycle (Krebs Cycle) (mitochondrial matrix)
4) Electron Transport System (Oxidative phosphorylation) (inner mitochondrial membrane)
Overall purpose: extract energy from glucose and transfer it to ATP through substrate-level phosphorylation and oxidative phosphorylation.

Glycolysis

Location: cytosol
Reactants: glucose, ADP + Pi, NAD+ (in steps that generate NADH)
Products: lactate or pyruvate, ATP, NADH
Net ATP: 2 ATP (glucose is phosphorylated in early steps consuming ATP; later steps generate ATP)
Key features:
- 9–10 steps total
- Quick production of ATP
- Produces pyruvate under aerobic conditions; lactate under anaerobic conditions
Core statement: Glucose (6-carbon) is phosphorylated and split into two 3-carbon molecules (G3P) which are ultimately converted to pyruvate or lactate depending on oxygen availability.
Specific transformation:
- Start with a 6-carbon ring/chain; convert into 2 × 3-carbon molecules (often glyceraldehyde-3-phosphate, G3P)
- End with lactate or pyruvate, with net ATP production and NADH generation.
- Representation of one phase:
  ext{Glucose} + 2~ ext{ADP} + 2~ ext{P}_i
  ightarrow 2~ ext{pyruvate} + 2~ ext{ATP} + 2~ ext{NADH} + 2~ ext{H}^+
Quick energy note: Glycolysis can operate rapidly to provide ATP before mitochondrial respiration can fully respond.

Intermediate Stage (Pyruvate Oxidation)

Location: inside the mitochondria (mitochondrial matrix)
Reactants: pyruvate, Coenzyme A (CoA), NAD+
Products: Acetyl-CoA, NADH, CO2
Significance: Links glycolysis to the Citric Acid Cycle by converting pyruvate to acetyl-CoA, releasing CO2 and generating NADH for the electron transport chain.
Key equation:
ext{Pyruvate} + ext{CoA} + ext{NAD}^+
ightarrow ext{Acetyl-CoA} + ext{NADH} + ext{CO}_2

Citric Acid Cycle (Krebs Cycle)

Location: inside the mitochondria (mitochondrial matrix)
Reactants: Acetyl-CoA, NAD+, FAD, ADP + Pi
Products: NADH, FADH2, CO2, ATP (as GTP in some steps)
Significance: completes oxidation of glucose-derived carbons; produces high-energy electron carriers (NADH, FADH2) used in oxidative phosphorylation.
Key outputs per acetyl-CoA enter: 3 NADH, 1 FADH2, 1 ATP (or GTP), 2 CO2 (per acetyl-CoA; double for one glucose)
Note: Net ATP yield from CAC is indirect; primary energy comes from NADH and FADH2 produced that feed the electron transport chain.

Electron Transport System (ETC) and Oxidative Phosphorylation

Step 1: Electron transfer
- NADH and FADH2 donate electrons to electron carriers (e.g., NADH dehydrogenase; ubiquinone Q; cytochromes in the inner mitochondrial membrane).
- Oxygen (O2) is the final electron acceptor, forming water: ext{O}2 + 4 ext{e}^- + 4 ext{H}^+ ightarrow 2 ext{H}2 ext{O}
Step 2: Proton pumping and gradient formation
- Movement of electrons pumps H+ ions from the matrix to the intermembrane space, creating a proton (H+) gradient (proton motive force).
- Result: higher H+ concentration outside than inside the matrix.
Step 3: ATP synthesis via ATP synthase (oxidative phosphorylation)
- H+ flow back down the gradient through ATP synthase, driving phosphorylation of ADP to ATP.
- Overall: O2 consumption, water formation, and large ATP yield.
- Summary equation for respiration (net):
  ext{C}6 ext{H}{12} ext{O}6 + 6~ ext{O}2
  ightarrow 6~ ext{CO}2 + 6~ ext{H}2 ext{O}
  ext{ADP} + ext{P}_i
  ightarrow ext{ATP}
Significance of oxidative phosphorylation:
- Primary source of ATP during sustained, aerobic exercise and many cellular processes.
- Efficient energy production by coupling electron transport to ATP synthesis.
Overall cellular respiration summary (locations and flow):
- Glycolysis: cytosol -> Pyruvate (cytosol) -> Pyruvate enters mitochondria
- Intermediate Stage: mitochondrial matrix -> Acetyl-CoA, NADH, CO2
- Citric Acid Cycle: mitochondrial matrix -> NADH, FADH2, CO2, ATP
- Electron Transport System: inner mitochondrial membrane -> ATP via ATP synthase; water formed at final acceptor site; O2 consumption
General energy balance in cellular respiration:
- Glucose oxidation products flow to NADH and FADH2 for ATP production
- Net ATP yield per glucose molecule is highest when O2 is present and the full aerobic pathway proceeds; glycolysis provides initial ATP and NADH.
Quick cross-reference equations:
- Glucose oxidation overview: ext{C}6 ext{H}{12} ext{O}6 + 6~ ext{O}2
  ightarrow 6~ ext{CO}2 + 6~ ext{H}2 ext{O}
- ATP synthesis: ext{ADP} + ext{P}_i
  ightarrow ext{ATP}
- Glycolysis outcome (net): ext{Glucose} + 2~ ext{ADP} + 2~ ext{P}_i
  ightarrow 2~ ext{pyruvate} + 2~ ext{ATP} + 2~ ext{NADH}

Summary of Cellular Respiration Stages

Glycolysis: location cytosol; substrates glucose; outputs 2 pyruvate, 2 ATP (net), 2 NADH; anaerobic vs aerobic end products (pyruvate vs lactate).
Intermediate Stage: location mitochondrial matrix; substrates pyruvate, CoA, NAD+; outputs acetyl-CoA, NADH, CO2.
Citric Acid Cycle: location mitochondrial matrix; substrates acetyl-CoA, NAD+, FAD, ADP+P_i; outputs NADH, FADH2, CO2, ATP.
Electron Transport System (ETC): location inner mitochondrial membrane; inputs NADH, FADH2, O2; outputs water, ATP; high ATP yield via oxidative phosphorylation.

Plasma Membrane and Cells – Structure, Types, and Roles

Learning Objectives (from pages 21, 27):
1) Describe the range of sizes and shapes of human cells and relate to function.
2) Describe basic features of a cell.
3) Describe the general structure and function of the plasma membrane.
4) Differentiate between the two types/classes of plasma membrane proteins based on their relative position in the membrane.
5) Name three major roles played by membrane proteins.
Range of cell sizes and shapes (context and examples):
- RBC: ~7 μm
- Mitochondrion: ~1 μm
- Skeletal muscle cell: 1–600 μm (long and multinucleated in some fibers)
- Neurons: can be very long (close to 1 m in extreme cases)
Relationship between cell size/shape and function: morphology supports specialized roles (e.g., elongated neurons transmit signals; small RBCs maximize surface area-to-volume; mitochondria in muscle cells support high energy demand).
Structure and components of the cell:
- Non-membrane-bound organelles:
- Ribosomes (free and fixed)
- Centrosome
- Proteasome
- Cytoskeleton
- Cytosol (intracellular fluid)
- Membrane-bound organelles:
- Nucleus, Nuclear envelope, Nucleoplasm, Nucleolus
- Rough Endoplasmic Reticulum (RER)
- Smooth Endoplasmic Reticulum (SER)
- Mitochondrion
- Golgi apparatus
- Peroxisome
- Lysosome
- Inclusions, Cytoplasm, Cytosol (intracellular fluid)
- Plasma membrane
- Modifications of plasma membrane (microvilli, vesicles)
- Cilia and Flagellum
Visual cues (from figures):
- Figure 4.4 Structural layout of cell components
- Figure 4.2 Range of cell sizes and examples
- Figure 4.3 Variety of cell shapes (skeletal muscle, RBC, neurons)

The Plasma Membrane: Structure, Proteins, and Roles

Structure and general function:
- A phospholipid bilayer with embedded proteins that regulate transport, signaling, and interaction with the extracellular environment.
- Provides a selective barrier and surface for communication with the extracellular environment.
Types of plasma membrane proteins by position:
- Peripheral proteins: anchored on one side of the membrane (exterior or interior); not embedded through the bilayer.
- Integral proteins: embedded within the membrane; many span the entire membrane; include channels and receptors.
- Receptors, channels, enzymes, and transporters can be integral or peripheral depending on subclass.
Three major roles of membrane proteins:
- Transport: channels and carriers that move ions and molecules across the membrane.
- Receptors: detect and relay signals from the extracellular environment to the cell interior.
- Enzymes: catalyze reactions at the membrane surface or within the membrane area.
Proteins associated with the plasma membrane (examples):
- Transport proteins: channels, carrier proteins, pumps
- Enzymes
- Receptors
- (Note: Some proteins provide structural support or participate in signaling cascades but are not listed here as separate categories.)

Review Questions and Practical Contexts

True/False: Another name for extracellular fluid is interstitial fluid.
- True
Question: Which of the following plasma membrane proteins are anchored to a single side of the membrane?
- Answer: Peripheral
- Options: A) peripheral B) receptor C) integral D) transport
Question: Which plasma membrane proteins can allow ions to move across the membrane?
- Answer: Integral (including channels) or transport proteins as appropriate; peripheral proteins generally do not form channels.
Real-world relevance and cautions:
- CAMELBAK: Overhydration can cause hyponatremia (reduced sodium concentration).
- Soy Sauce Challenge: High sodium intake can affect fluid and electrolyte balance.
Quick recap of key terms and definitions:
- Oxidative phosphorylation: The process by which ATP is produced in the mitochondria using a proton gradient established by the electron transport chain.
- Glycolysis: Cytosolic breakdown of glucose to pyruvate, yielding ATP and NADH rapidly.
- Pyruvate: The end product of glycolysis; enters mitochondria for further oxidation if oxygen is present.
- Acetyl-CoA: Activated two-carbon donor that enters the Citric Acid Cycle.
- NADH and FADH2: Electron carriers that feed the Electron Transport System.
Exit poll and reflections:
- An open-ended prompt asking what was most confusing about the lecture; consider topics like the coupling of glycolysis to oxidative phosphorylation, or how proton gradient drives ATP synthesis.
Connections to broader themes:
- Energy systems integrate biochemistry with physiology: immediate energy (ATP/PCr), short-term energy (glycolysis), and long-term energy (aerobic respiration).
- The plasma membrane not only regulates transport but also coordinates signaling and homeostasis, essential for muscle function, nerve signaling, and metabolic control.
Equations and representative constants (for quick reference):
- ATP synthesis reaction: ext{ADP} + ext{P}_i
  ightarrow ext{ATP}
- Glycolysis net ATP (per glucose): ext{Net ATP} = 2
- Glucose oxidation (overall): ext{C}6 ext{H}{12} ext{O}6 + 6~ ext{O}2
  ightarrow 6~ ext{CO}2 + 6~ ext{H}2 ext{O}
- Pyruvate oxidation to Acetyl-CoA (intermediate stage): ext{Pyruvate} + ext{CoA} + ext{NAD}^+
  ightarrow ext{Acetyl-CoA} + ext{NADH} + ext{CO}_2
- Proton motive force and ATP synthase concept:
- Proton pumping creates an electrochemical gradient used by ATP synthase to convert ADP + Pi into ATP.

Quick Concept Map (to review before the exam)

Energy carriers: ATP, PCr, glycogen, lipids, proteins
Four stages of cellular respiration: Glycolysis → Intermediate Stage → CAC → ETC
Key locations: cytosol, mitochondrial matrix, inner mitochondrial membrane
ATP yield drivers: substrate-level phosphorylation (glycolysis, CAC) and oxidative phosphorylation (ETC)
Plasma membrane roles: transport, signaling, enzymatic activity; protein topology (peripheral vs integral)
Cell diversity: size/shape vs function; organelle distribution supports function