Lecture 8 (cellular respiration)

Question 1

Photosynthesis occurs in

Answer 1

Plants only

Question 2

Cellular respiration occurs in

Answer 2

Plants and animals

Question 3

Photosynthesis uses an

Answer 3

Energy rich molecule

Question 4

Cellular respiration creates an

Answer 4

Energy poor molecule

Question 5

What are the major energy requirements for a cell?

Answer 5

The cell needs energy…

1- for mechanical work such as motor proteins (movement requires energy)
2- to make new materials e.g. for growth and replacement (organelles/cells are constantly being replaced)
3- for transport e.g. transport of molecules across membranes (subcellular organisation is important as things have to be in the right place at the right time and in order for things to move, especially against the concentration gradient, the input of ATP is required) (Taking the phosphate group off of ATP and then using that energy to drive the transport protein for example resulting in ADP)
4- to maintain order - it takes ATP in order to maintain the status quo

Question 6

Mitochondria

Answer 6

The site of cellular respiration

An organelle found in large numbers in most eukaryotic cells that serves as the site of cellular respiration and energy production; using oxygen to break down organic molecules and synthesise ATP.

Plural: Mitochondria

Question 7

Equations for cellular respiration

Answer 7

C6H12O6 + 6O2 —> 6CO2 + 6H2O +Energy

conversion of chemical energy

Question 8

Mitochondria structure - general

Answer 8

it is an organelle

It is 1-10 microns long

1-1000s per cell as it is dependent on what the energy demand is for a certain cell type (e.g. muscle cells need lots of mitochondria as more ATP is required)

Contains mitochondrial DNA and ribosomes. Mitochondria have their own genomes. This produces some but not all mitochondrial proteins. They do this because they used to be able to survive on their own (endosymbiosis theory), however mitochondria can no longer survive on their own.

Question 9

What is essential for cellular respiration?

Answer 9

The compartments of the mitochondria are essential for cellular respiration

Question 10

Cellular respiration

Answer 10

The catabolic pathways of aerobic and anaerobic respiration, which break down organic molecules and use an electron transport chain for the production of ATP.

A process by which ATP is formed

Question 11

Mitochondria structure - parts of a mitochondrion

Answer 11

Has two membranes - an inner and an outer mitochondrial membranes (the double membrane is important)

Mitochondrial metric inside the inner membrane

Inner membrane is highly folded (cristae) which is functionally important (provides surface area for proteins to bind)

Inter membrane space is functionally impotents (it has a concentration gradient of protons)

Question 12

Overview of cellular respiration

Answer 12

Harvesting chemical energy from glucose occurs in three stages - glycolysis, pyruvate oxidation and citric acid cycle and oxidative phosphorylation

Chemical energy is converted from one form to another

From glucose to ATP - an energy carrier used by the cell

The structure of mitochondrion enables the proton gradient to be established across the inner membrane and this drives the production of ATP

Glucose and oxygen are consumed. Carbon dioxide and water and ATP are produced through this process

Question 13

What is NADH?

Answer 13

This is formed when electrons are transferred to the high energy electron carrier NAD+ which then in turn makes NADH

Question 14

Glycolysis

Answer 14

Stage one of cellular respiration

In the cytosol, glucose is converted into a smaller molecule called pyruvate (creates 2 pyruvate which are three carbon molecules). This generates 2ATP (a small amount of energy) and electrons are transferred to the high energy electron carrier NAD+ which makes NADH

Question 15

Pyruvate oxidation and citric acid cycle

Answer 15

Stage 2 of cellular respiration

This process occurs in the mitochondrial matrix. Pyruvate is converted into acetyl CoA. Acetyl CoA then enters the citric acid cycle. The output of this stage is the energy carrier ATP and high energy electrons carriers NADH and FADH2

Pyruvate oxidation converts pyruvate—a three-carbon molecule—into acetyl CoA. The citric acid cycle is a chemical cycle which oxidises acetyl CoA to carbon dioxide, completing the metabolic breakdown of glucose. Together with pyruvate oxidation, the second major stage in cellular respiration. Sometimes called the Krebs cycle.

This stage generates a little ATP and some more high energy electrons

Question 16

Summary of stages 1 and 2 of cellular respiration

Answer 16

Glycolysis and pyruvate oxidation and citric acid cycle. Started with glucose and now the output is 4 ATP molecules and some NADH and FADH2 (the next step converts NADH and FADH2 into ATP)

Question 17

What is FADH2?

Answer 17

Molecule that, along with NADH, carries high energy electrons

Question 18

Oxidative phosphorylation - summary

Answer 18

The production of ATP using energy derived from reactions in the electron transport chain; the third major stage of cellular respiration.

Lots of ATP is formed in this step

This final step occurs on the membrane, a combination of high energy electrons, proteins and the inner membrane produces a large amount of ATP

This stage occurs in the inner membrane of the mitochondrion

There are two parts to oxidative phosphorylation - electron transport chain (electrons from NADH and FADH2) and chemiosmosis (ATP production)

Question 19

The electron transport chain

Answer 19

Part 1 of oxidative phosphorylation (stage 3 in cellular respiration)

Electron carriers (NADH and FADH2) shuttle high energy electrons to the inner mitochondrial membrane

These electrons move through protein complexes embedded in the inner membrane

As the electrons move protons (H+) are pumped across the membrane. H+ are moved from inside the mitochondrial metric to the inter-membrane space (across the inner membrane). The energy of the high energy electrons allows protons to be pumped across the membrane

A proton gradient is generated - Protons (H+) accumulate in the inter membrane space. Making the proton concentration different on either side of the inner mitochondrial membrane. The compartments of the mitochondrion are essential for this to happen. This accumulation of protons are crucial for the next step. (without the proton gradient, you wouldn’t be able to drive ATP synthase)

Floating on the lipid bilayer are big protein competes (there are 4 protein complexes)

Think of it as a continual chain of electrons moving through. If electrons aren’t leaving complex 4, then you cannot get anymore electrons moving through the chain. This means that a final electron receptor is needed so that the electron has somewhere to go. As a result of this process you now have a much lower energy electrons which goes to oxygen, oxygen is known as the terminal electron acceptor and it is the last place the electrons go as they come through the electron transport chain (water is a byproduct) (therefore no oxygen, no respiration)

Question 20

Chemiosmosis

Answer 20

Part 2 of oxidative phosphorylation (stage three of cellular respiration)

The inner mitochondrial membrane contains the protein complex known as ATP synthase (a single unit enzyme)

This complex spans the membrane from the inter membrane space to the mitochondrial matrix (so protons can move through it as they move back into the mitochondrial matrix

The proton gradient across the inner membrane powers the ATP synthesis (protons move from high to low concentration through ATP synthase)

ATP synthase converts : ADP + Pi —> ATP (As protons move from the inter membrane space back to the mitochondrial membrane, the ATP synthase turns and catalyses the production of ATP

Question 21

ATP

Answer 21

Adenosine Triphosphate: An adenine-containing nucleoside triphosphate that releases free energy when its phosphate bonds are hydrolyzed (broken by chemical reactions).

ATP is an energy carrier

ATP enables the controlled release of energy.(can be used to drive specific functions) (Allows the release of a known amount of energy …can remove phosphate off ATP and create a little packet of energy) If you just catalysed the breakdown of glucose, a lot of energy is released in an uncontrolled way and associated with this release is an increase in heat which would kill the cell and therefore there needs to be a controlled release of energy

Regeneration of ATP is essential. The cell continuously uses and regenerates ATP (ATP synthase is constantly making ATP). The cell uses energy for cellular work.