HL Biology Unit 8.1-8.2 Cell Respiration

Metabolism

All chemical reactions (catabolic+anabolic) that occur in a living organism

Cytosol

The portion of the cytoplasm that is NOT contained WITHIN membrane-bound organelles

Metabolic Pathways

Linked series of chemical reactions occurring within a cell that are enzyme-mediated, often with diff. enzymes needed for each stage

What is the difference between linear and cyclical metabolic pathways?

Linear: Final product moves on to serve a different purpose

Cyclical: Final product feeds the initial reaction (ex. Urea cycle, where ornithine is re-used)

What are properties (4) of Enzymes?

• Globular Proteins

• Increases reaction rate by decreasing activation energy

• Undergo conformational change to create induced fit for substrates

• Shape determines substrate specificity - which substrate it binds to

Enzyme Inhibitors

Molecules that block enzyme function either competitively or non-competitively

What is the difference between competitive and non-competitive enzyme inhibitors? Visualize their effects on a graph.

Competitive: Allow reactions via enzymes to reach their maximum rate of reaction (just slower) because substrates will eventually reach enzymes before inhibition happens

Non-competitive: Do NOT allow reactions to reach maximum rate because a certain amount of total enzymes available will be “poisoned”, not allowing for the substrate to bind with them bc of active site shape deformation regardless of how much substrate is available

What is an example of temporary compettive inhibition?

Statins are a group of medicines used to lower low-density lipoproteins (LDL)/ “bad” cholesterol production in the liver by temporarily binding to the active site of HMG-CoA Reductase 

What is an example of permanent competitive inhibition?

Penicillin irreversibly binds to the transpeptidase active site, which prevents bacterial cell walls from being built, effectively killing any unwanted bacteria. 

What is end-product inhibition? 

a type of enzyme inhibition used to regulate metabolic pathways, where the final product regulates the first reaction to prevent overproduction 

What is an example of end-product inhibition?

Isoleucine functions as an end-product inhibitor, creating a self-regulated pathway. If there is a sufficient/low concentration of isoleucine, the active site from the 1st enzyme is free, and if there is a high concentration, the accumulated isoleucine binds to the 1st enzyme to prevent further production

(also, threonine is the initial substrate that turns into isoleucine).

What is ATP?

Adenosine triphosphate is a nucleotide that is used for energy storage/transfer of energy between processes and parts of the cell

What are characteristics (5) of ATP that make it suitable for its function?

1. Water soluble, so it can move freely through the cytoplasm to reach different organelles

2. Stable at neutral pHs, which matches the cytoplasm

3. Its movement can be controlled because as a large, negatively charged particle, it can’t pass through the phospholipid bilayer

4. The 3rd phosphate group can be easily removed by hydrolysis to create ADP

5. The transformation of ATP → ADP creates just enough energy for cell processes but not enough so that it would be wasted as heat

What processes is ATP used for?

Synthesizing Macromolecules, Active Transport, Movement

What is an example of ATP being used to synthesize macromolecules?

Anabolic reactions are endothermic and therefore required energy - 1 or more ATP molecules are used each time a monomer is linked ex. DNA (replication), RNA (transcription), Proteins (translation)

What is an example of ATP being used in active transport?

Pumping ions across the concentration gradient requires energy: ATP changes pumps from their stable state to their less stable state (but ATP is not required for the pumps to revert back into their stable state

What is an example(s) of ATP being used for movement in/of the cell? Which type of movement requires more energy?

• Chromosomes moving to opposite poles during mitosis (anaphase)

• Cells pinching apart during mitosis

• Vesicles moving to transport materials

• Phagocytes using locomotion; changing their shape to move to sites of infection

• Muscle cell contractions occur when large arrays of myosin and actin filaments slide on top of e/o

Movements require changes in shape require the most energy.

What is the conversion of ATP → ADP for? What’s a downside and an IRL example that overcomes it?

This conversion releases energy to be used by the cell, but this process is not 100% efficient bc some is lost as heat, and there’s only a little bit of ATP in our bodies at a time (0.2 mol).

The six-eyed spider can remain motionless to conserve ATP

What is cell respiration?

Energy released by oxidizing carbs/fats/proteins

What happens when we use up all of our ATP?

• Neurons can’t convey impulses

• Muscles stop contracting, leading to cramps

• Cells degrade irreparably in minutes

How is ATP and ADP regenerated?

ATP = cell respiration

ADP = active cell processes

What are respiratory substrates?

Compounds that are oxidized during cell respiration to create ATP

What kinds of respiratory substrates are used for plants and humans?

Humans = food (glucose, fatty acids)

Plants = carbs or lipids from photosynthesis

What is the relationship between gas exchange and cell respiration?

• They’re both independent processes that work through simple diffusion.

• Gas exchange ensures O and CO₂ balance

• Simple diffusion of gases is only possible because of the concentration gradient created by cell respiration

Differences in types of cell respiration:

Differences (5) between anaerobic and aerobic respiration

Aerobic

• Oxygen used as electron acceptor

• Uses carbs like glucose, lipids like fats/oils, and amino acids after deamination

• Waste: CO₂+H₂O

• High ATP Yield (30+ molecules/glucose)

• Starts in cytoplasm, also occurs in mitochondria

Anaerobic

• No oxygen used

• Only carbs used

• Waste: CO₂ + Lactate or Ethanol

• Lower ATP yield (2 molecules/glucose)

• Reactions only in cytoplasm

Describe respiration in muscles

• Aerobic normally, anaerobic in spurts for max power

• Lactic acid waste buildup from anaerobic resp. needs to be broken down, which uses O₂ → overuse causes oxygen debt, which is why we run out of breath

How can rate of respiration be measured?

• O₂ uptake

• CO₂ production

• Amount of glucose/other respiratory substrates consumed

What are electron carriers?

Substances that can accept/lose electrons reversibly, often linking oxidation + reduction (ex. NAD, nicotinamide adenine dinucleotide)

Explain the two ways that NAD can act as an electron carrier

By Losing H+ Atoms

NAD + 2H⁺ + 2e^- → NADH⁺ (reduced NAD) + H⁺

Each H contains 1p and 1e, NAD accepts 2e and one H⁺ so the other H⁺ is released

By Gaining O Atoms

Nitrifying Bacteria: NO₂^- + (1/2)O₂ → NO₃^-

What is Glycolysis?

The 1st step of AEROBIC respiration (and technically before anaerobic respiration) in the cytoplasm that converts glucose/other monosaccharide substrates into pyruvate, producing a small ATP yield (w/o oxygen, but later steps need it).

What is phosphorylation?

The addition of phosphate (PO₄^3-) to a molecule

Describe the 1st step of Glycolysis

Phosphorylation of Glucose

• Usually occurs through ATP transferring a phosphate group to glucose

• Requires energy to make molecules more unstable, and therefore more likely to participate in later reactions

1. Glucose→ (ATP→ADP) Glucose-6-phosphate

2. Glucose-6-phosphate →  Fructose-6-phosphate

3. Fructose-6-phosphate → (ATP→ADP) Fructose-1, 6-bisphosphate

Describe the 2nd step of Glycolysis

Lysis

Fructose-1, 6-bisphosphate → 2 triose phosphate

Describe the 3rd step of Glycolysis

Oxidation

• Oxidation of sugar to produce organic acid

Triose phosphate + phosphate → (NAD → NADH) bisphosphoglycerate 

Describe the 4th step of Glycolysis

ATP Formation

bisphosphoglycerate →→ (ADP→ATP) (ADP→ATP) pyruvate

(the BI part allows two molecules of pyruvate, so this yields 2 ATP. There are 2 bisphosphoglycerates made per glucose, so the total yield in this stage is 4 ATP)

What is the final yield after the 4 stages of glycolysis?

• 1 glucose (6 carbon) is converted to 2 pyruvates (3 carbons each)

• 2 NAD → 2 NADH

• 2 ATP used (stage 1) + 4 ATP produced (stage 4) = 2 ATP net yield

What is the Link Reaction?

The reaction that links glycolysis to the krebs cycle by turning pyruvate (the product of glycolysis) into Acetyl-CoA (the first reactant in the krebs cycle)

What is the Krebs Cycle?

The oxidation of Acetyl-CoA in the mitochondria matrix to produce a small amount of ATP and electron carriers (NADH and FADH₂) required to facilitate the electron transport chain, which makes most of the ATP in aerobic respiration.

How do the number of carbons change throughout the Krebs Cycle?

1. Pyruvic Acid (3C)

2. 1st decarboxylation forms Acetyl-CoA (2C)

3. Citrate (6C)

4. 2nd decarboxylation (5C)

5. 3rd decarboxylation (4C)

6. Final product, oxaloacetate (4C)

What are the final products of the Link Reaction + the Krebs cycle?

Per 1 glucose (2 pyruvate) made in glycolysis:

• 8NADH

• 2 FADH₂

• 2 ATP (will be used)

• 6 CO₂ (waste)

What is Oxidative Phosphorylation?

A process occurring in the intermembrane space of the mitochondria used to form ATP using electron carriers (protein pumps) energized by electrons from other electron carriers (NADH, FADH₂).

This process is divided into the Electron Transport Chain and Chemiosmosis

What is the Electron Transport Chain?

A chain of proteins that transfer electrons to create a chemical gradient between the intermembrane space and matrix of the mitochondria, used to help ATP synthase activity in oxidative phosphorylation

What is the final electron acceptor in the Electron Transport Chain? What is produced after?

O₂ accepts the last H+ ion (electron) to form H₂O as waste

What is ATP Synthase?

An enzyme that uses the concentration gradient of ions created by the ETC as kinetic energy to combine ADP + Pi (phosphate) → ATP in a process called chemiosmosis

What is chemiosmosis?

The passive transport of protons in the intermembrane space down the concentration gradient back into the mitochondrial matrix

What other material can be oxidized the same way as pyruvate in the link reaction to start the Krebs Cycle?

Fatty acids

What are the characteristics of using fats as a source of energy for cell respiration?

• Aerobic only

• Each 2 carbon fragment in a fatty acid can be used to make 1 Acetyl-CoA

Why do fatty acids offer more energy than carbs?

• They contain more carbon to make Acetyl-CoA than glucose

• Triglycerides are less oxidized, so they have more C-C and C-H bonds and therefore more potential oxidation reactions that could provide energy

Compare and Contrast the use of carbs and fatty acids as energy for cell respiration

Carbs

• Anaerobic or aerobic process

• Occurs in glycolysis

Fatty Acids

• Aerobic only

• More carbon → More Acetyl-CoA per gram

• More reduced → more oxidation → greater energy release

Both

• Both undergo oxidation to release energy

• Can be used to make Acetyl-CoA

Label the parts of the mitochondria

A. Intermembrane space

B. Outer membrane

C. Cristae (folds of inner membrane)/Inner Membrane

D. Matrix

How is NAD regenerated anaerobically?

Lactic Acid Fermentation

• 2 NAD used in glycolysis to form 2NADH

• 2NADH used to convert pyruvate into lactate/ethanol, so 2 NAD regained

Pyruvate → (NADH→NAD⁺) Lactate

Pyruvate → (NADH→NAD⁺) Ethanol

What is the purpose of anaerobic respiration?

To produce a small yield of ATP and to regenerate NAD

Why, theoretically, can NAD be regenerated indefinitely? Why could this not be true?

Glycolysis uses 2NAD (to make NADH) and fermentation replaces it with 2NAD (by oxidizing NADH), so NAD can be recycled indefinitely. This occurs unless:

1. There aren’t stores for glucose

2. All ADP is converted into ATP (glycolysis wouldn’t have to occur if this was the case)

3. There is a dangerously high concentration of lactate produced

Compare lactic acid and alcohol fermentation

• Anaerobic

• Occur in Cytoplasm

• Small ATP Yield

• Starts with glycolysis to make pyruvate, which is then used for their processes

What is the 1st step of anaerobic respiration in yeast?

CO₂ is removed from pyruvate by decarboxylation → ethanal

What is the 2nd step of anaerobic respiration in yeast?

2H is transferred from NAD to ethanal → ethanol

Both steps together: pyruvate → (CO₂ waste) ethanal → (NADH→NAD) ethanol

What is a facultative anaerobe and an example?

An anaerobic organism that uses both aerobic respiration or fermentation (anaerobic) depending on presence of oxygen