Cellular Respiration: Krebs Cycle

Why is it also called the citric acid cycle?

Because it refers to the first molecule that forms during the cycle's reactions - citrate/citric acid

What is the citric acid cycle?

The central driver of cellular respiration

What is the purpose of the krebs cycle?

It takes acetyl CoA and in a series of redox reactions harvests much of its bond energy in the form of NADH, FADH2 and ATP molecules

What are the reduced electron carriers and what are their jobs?

NADH and FADH2 -- they will pass their electrons into the ETC and go through oxidative phosphorylation and generate most ATP produced in cellular respiration

OVERVIEW OF THE CITRIC ACID CYCLE/KREBS CYCLE/TRICARBOXYLIC ACID CYCLE

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Where does krebs occur in eukaryotes?

Matrix of the mitochondria

Where does krebs occur in prokaryotes?

both take place in the cytoplasm

How many steps are in krebs?

8

Why does krebs occur twice?

Each stage in the cycle occurs twice for every glucose molecule that enters glycolysis, because 2 pyruvate molecules are produced for each glucose

STEPS OF THE CITRIC ACID CYCLE

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Step 1

Acetyl CoA joins with a four carbon molecule (oxaloacetate) releasing the CoA group and forming a six carbon molecule called citrate

Step 2

Citrate is converted into its isomer -- isocitrate

Step 3

Isocitrate is converted into a-ketogluterate by losing CO2 and two hydrogen atoms that reduce NAD+ to NADH [NAD+ reduced to NADH]

Step 4

A-ketogluterate is converted to succinyl CoA. A CO2 is removed, coenzyme is added, and two H atoms reduce NAD+ to NADH

Step 5

Succinyl CoA is converted to succinate --> ATP is formed by substrate level phosphorylation and coenzyme A is released

Step 6

Succinate is oxidized forming another four carbon molecule called fumarate [Two H atoms reduce FAD into FADH2]

Step 7

Water is added to the four carbon molecule fumarate converting it into another four carbon molecule called matalate

Step 8

Oxaloacetate is regenerated by the oxidation of malate and another molecule of NAD+ is reduced to NADH

What's the overall equation for krebs FOR ONE CYCLE?

oxaloacete + acetyl CoA + ADP + Pi + 3 NAD+ + FAD --> CoA + ATP + 3 NADH + FADH2 + 2 CO2 + oxaloacetate

How come there's only one ATP or GTP?

The krebs cycle does not produce much ATP but it can make a lot of ATP indirectly by producing NADH and FADH2 molecules

What is the purpose of the electron carriers - NADH and FADH2?

They will deposit electrons into the ETC to drive synthesis of ATP molecules through oxidative phosphorylation