Cellular Respiration

1
Cellular Respiration

• Glycolysis
• Preparatory reaction
• Citric acid (krebs) cycle
• Electron transport chain

2
Glycolysis

• Occurs outside mitochondria
• Breaks down glucose into two pyruvate molecules
• Evolutionary speaking, glycolysis occurs in all
  organisms, meaning it probably evolved before the
  citric acid cycle and the electron transport chain

3
Steps in Glycolysis

• Begins when glucose is activated with two ATP
  molecules, the glucose splits into two C
  molecules known as G3P.
• G3P is then oxidized, removing electrons and H
  ions.
• The lost electrons and H ions are then accepted
  by NAD resulting in two NADH.
• G3P oxidation results in the production of 4
  high-energy phosphate groups which make 4 ATP
  molecules, called substrate-level
  phosphorylation.
• There is a net gain of only 2 ATP molecules in
  glycolysis because 2 of the ATP molecules are
  used in supplying energy for the reaction
• What happens next depends on if O2 is available
  or not. If it is available, pyruvate enters and
  C.R. ensues. If not, fermentation occurs, and
  pyruvate is reduced.

4
Preparatory Reaction

• Connects glycolysis to the citric acid cycle
• converts pyruvate to a 2-carbon acetyl group and
  attaches it to coenzyme A resulting in acetly-CoA
  through a redox reaction.
• The reaction occurs twice for each glucose
  molecule

5
Citric Acid (krebs) cycle

• Occurs in the matrix of the mitochondia
• Sometimes called the krebs cycle because it was
  named for sir Hans Krebs who described the
  reaction in the 1930s.
• Begins by the addition of a 2-carbon acetyl group
  to a 4-carbon molecule forming a 6-carbon citric
  acid molecule
• In the reactions that follow, at three different
  times, two electrons and one H ion are accepted
  by NAD , forming NADH
• At one time in the cycle, two electrons and one H
  ion are accepted by FAD, forming FADH2
• Some energy is released and is used to make ATP
  by substrate-level phosphorylation,
• One high-energy metabolite accepts a phosphate
  group and ADP to ATP in the reaction.
• For each glucose molecule that goes in, the
  citric acid cycle turns twice.
• The products of the cycle are 4 CO2, 2 ATP, 6
  NADH and 2 FADH2

6
The electron transport chain

• Takes place in the cristae of the mitochondria,
  in which electrons are passed from carrier to
  carrier
• Some carriers are cytochrome molecules(complex
  carbon rings with iron in the center)
• NADH and FADH2 carry the electrons through the
  system
• Each time the electrons are passed on, NADH gives
  up its electrons and becomes NAD then picks up
  electrons, therefore they are reduced.
• ATP is released at each redox (reduction)
  reaction
• Oxygen must be present for this to work,
  therefore this process is also called oxidative
  phosphorylation
• Oxygen accepts electrons in the reaction and
  combines with hydrogen ions to form water.
• The electrons are being delivered to the system
  by FADH2, at this time two ATP molecules are
  formed
• Coenzymes and ATP in the system undergo recycling.

7
For Monday Nov. 10

• Study for a 20-point quiz (credit)
• Beginning lab on CR
• Study session after school TH 11/13
• TEST will be on Monday 11/17
• Lab Report for CR will also be due on that day
• Homework complete/review the rest of the notes
  online at kauscience.k12.hi.us