Cell Bio Exam 2 Lectures 22a, 22b, and 23

Photosynthesis Reaction

6 CO2 + 12 H2O + sunlight ➔ C6H12O6 (glucose) + 6 H2O + 6 O2

Two Main Stages of Photosynthesis

Light-dependent reactions (in thylakoids) and the Calvin Cycle (in the stroma)

Photosystem II (PS II)

Uses the P680 reaction center; splits water molecules to steal electrons and releases oxygen

Photosystem I (PS I)

Uses the P700 reaction center; takes electrons to turn NADP+ into NADPH

Electron Transport System (ETS)

Pumps protons (H+) into the lumen to build a pressure gradient that spins ATP Synthase to make ATP

Photosynthesis vs. Cellular Respiration

They form a perfect loop; the products of one are the exact starting ingredients for the other

Calvin-Benson Cycle

Takes invisible CO2 from the air and "fixes" it into a physical 3-carbon sugar called G3P

Rubisco

The most abundant enzyme on Earth; grabs CO2 to start the Calvin Cycle, but has a fatal flaw of accidentally grabbing oxygen

Photorespiration

The wasteful mistake when Rubisco grabs oxygen instead of CO2 (happens in hot/dry weather when stomata close and trap O2 inside)

C4 Plants

Outsmart photorespiration using spatial separation (PEP Carboxylase works in mesophyll cells, Rubisco hides safely in bundle sheath cells)

PEP Carboxylase

The enzyme used by C4 and CAM plants that grabs CO2 perfectly because it NEVER accidentally grabs oxygen

CAM Plants

Desert plants that use temporal separation (open stomata at night to hoard CO2, close them during the hot day to save water)

Bacterial Fission

Super simple division: copy the circular DNA, stretch the cell out, separate the DNA, and pinch the cell in half

Eukaryotic Cell Cycle

Way more complex than fission; strictly regulated by checkpoints and uses mitosis

Interphase

The prep phase before division (G1, S, and G2); the cell looks inactive here because DNA is not condensed yet

G1 and G2 Phases

The specific parts of interphase strictly dedicated to cell growth and checking for errors

S Phase

The specific part of interphase strictly dedicated to DNA replication

M Phase

The actual division phase where chromosomes condense, the spindle forms, and the cell splits

MPF (Maturation Promoting Factor)

The master switch that forces a cell to enter M-phase; made of Cyclin B and Cdk1

How MPF turns ON

Cyclin B builds up during interphase and binds to Cdk1 to activate it

How Cdk1 works

Acts like a boss giving orders by phosphorylating target proteins (like phosphorylating lamins to break down the nuclear envelope)

How MPF turns OFF

When M-phase is over, Cyclin B gets destroyed, turning Cdk1 off so the cell can exit division

The Cyclin/Cdk System

How the whole cell cycle is timed; different cyclins pop up at specific times to activate different Cdks for each phase