Your favorite topic - everything Krebs and like Flashcards
What is a metabolic pathway?
A metabolic pathway is a series of enzyme-catalyzed chemical reactions.
Can be:
Linear (e.g. glycolysis)
Cyclic (e.g. Krebs cycle)
What is cell respiration?
The process by which organic compounds (mainly glucose) are broken down to produce ATP.
Main stages:
Glycolysis – cytoplasm
Link Reaction & Krebs Cycle – mitochondrial matrix
Electron Transport Chain & Chemiosmosis – inner mitochondrial membrane
What happens in Glycolysis?
Occurs in both aerobic & anaerobic respiration.
In CYTOPLASM
Converts glucose (6C) → 2 pyruvate (3C)
Net gain: 2 ATP, 2 NADH
What are the steps of glycolysis?
- Phosphorylation – 2 ATP used to add phosphates to glucose.
- Lysis – splits 6C sugar into two 3C sugars.
- Oxidation – NAD+ gains H → NADH.
- ATP formation – 4 ATP made (2 net)
What happens during the link reaction?
- Pyruvate (3C) → Acetyl-CoA (2C)
- CO₂ released, NADH produced
- Links glycolysis to Krebs cycle
Happens in the mitochondrial matrix
What happens in the Krebs cycle?
Acetyl-CoA (2C) enters, joins a 4C molecule → 6C
Through a cycle, regenerates 4C compound
For 1 Acetyl-CoA, yields:
3 NADH
1 FADH₂
1 ATP
2 CO₂
✌ Happens twice per glucose!
What happens in the Electron Transport Chain?
- NADH & FADH₂ donate electrons to ETC in the inner mitochondrial membrane.
- Electrons pass through carriers, releasing energy.
- This energy pumps H⁺ ions into intermembrane space → builds proton gradient.
What is chemiosmosis?
- H⁺ ions flow back through ATP synthase (enzyme channel).
- This flow powers ATP production – oxidative phosphorylation.
- Final electron acceptor = oxygen, which combines with H⁺ to make H₂O.
💥 Produces: ~34 ATP from one glucose in aerobic conditions.
Constrast aerobic to anarobic respiration?
Aerobic: oxygen required, located in the mitochondria, products: CO₂ + H₂O + lots of ATP, yield ~36-38 ATP per glucose, high efficiency
Anaerobic: No oxygen required, located in cytoplasm, Products: Lactate (animals) / Ethanol + CO₂ (yeast), yield Only 2 ATP per glucose, low efficiency
What is photosynthesis?
Definition: Photosynthesis is the process by which plants convert light energy into chemical energy, storing it in the form of glucose.
6Carbon Dioxide + 6 Water –> Glucose + 6Oxygen
What is the structure of a chloroplast?
Outer membrane: protection.
Thylakoids: flattened sacs where light-dependent reactions occur.
Grana: stacks of thylakoids, increase surface area.
Stroma: fluid-filled space for light-independent reactions (Calvin cycle).
Thylakoid space (lumen): proton accumulation here drives ATP synthesis.
How to convert light energy into ATP and NADPH?
- Photolysis: Water is split → releases e⁻, H⁺, and O₂.
- Excitation of electrons: Light excites electrons in chlorophyll (PSII).
- Electron transport chain: Electrons move → energy pumps H⁺ into thylakoid space.
- Chemiosmosis: H⁺ flows back through ATP synthase → makes ATP.
- Electron transfer to PSI: Electrons are re-energized and reduce NADP⁺ → NADPH.
💡 Products:
ATP (via photophosphorylation)
NADPH
O₂ (by-product)
What are the steps of the Calvin Cycle in the stroma?
Purpose: Use ATP & NADPH to fix carbon into glucose.
Phases:
1. Carbon fixation:
Enzyme Rubisco fixes CO₂ to RuBP (5C) → unstable 6C compound → 2 PGA (3C).
2. Reduction:
PGA is reduced using ATP & NADPH → forms G3P (triose phosphate).
3. Regeneration:
Some G3P used to regenerate RuBP.
Every 6 CO₂ makes 1 glucose (requires 18 ATP & 12 NADPH).
What are the properties of Xylem?
Xylem (Water & minerals – one way up):
Made of dead cells, lignified for support.
Transport is passive: transpiration pull, capillary action, root pressure.
What is transpiration?
Transpiration:
Loss of water vapor from stomata in leaves.
Creates negative pressure → water pulled up from roots.
Controlled by guard cells.
What are the properties of phloem?
Phloem (Sugars – bidirectional):
Made of living sieve tube cells and companion cells.
Uses active transport → called translocation.
Source to Sink:
Sugars move from source (leaf) to sink (root, fruit) using pressure flow mechanism.
What are auxins?
Plant hormones that stimulate cell elongation in shoots, inhibit it in roots.
Produced in apical meristems.
What is phototropism?
Shoots bend toward light.
Auxin redistributed to shaded side → cells elongate → bend toward light.
What is gravitropism?
Roots grow toward gravity, shoots grow against gravity.
Auxin accumulates on lower side:
In roots: inhibits growth → root bends down.
In shoots: promotes growth → shoot bends up.
What are competitive inhibitors?
Inhibitor mimics substrate and binds to the active site.
Can be overcome by increasing substrate concentration.
🔬 Example: Malonate competes with succinate in Krebs cycle.
What is an allosteric inhibitor?
An allosteric inhibitor is a type of molecule that binds to an enzyme at a site other than the active site. This special site is called the allosteric site.
🔍 Here’s what it does:
When the inhibitor binds to the allosteric site, it causes a change in the enzyme’s shape.
This change can alter the shape of the active site so that the enzyme can no longer bind to its substrate effectively.
As a result, the enzyme activity decreases or stops.
