Biology - C1.2 Cell respiration

What is the structure of ATP?

ATP is a nucleotide with a nitrogenous base (Adenine), a pentose sugar (ribose) and 3 phosphate group.

Full name of ATP

Adenosine Triphosphate

What does ATP do?

ATP is the energy currency of the cell because it is used for energy storage and transport.

What are the properties of ATP fulfill this function?

It is soluble so it can move through the cell, it is stable at the pH level of cytoplasm, it can’t diffuse out of the cell so it can’t move freely through the membrane. The third phosphate group can be easily removed.

How is energy formed from ATP?

When the third phosphate is is removed by hydrolysis there is a small, sufficient amount of energy released.

Life processes within cells that require ATP for energy

• Synthesising macromolecules, anabolic reactions (such as making polymers/DNA and RNA transcription/translation) require ATP

• Active transport across membrane, e.g. with pump proteins

• Movement inside the cell (e.g. chromosomes during mitosis or vesicles inside cell) or changing the shape of the cell (e.g. muscles contracting)

Hydrolysis and condensation reactions with ATP

A hydrolysis reaction with ATP would release 1 phosphate and some energy, making ADP.

A condensation reaction is the opposite and requires energy and releases water.

Cell respiration definition

A system for producing ATP within the cell using energy released from carbon compounds like but not limited to fatty acids and glucose.

Cell respiration vs. gas exchange

Gas exchange is when oxygen and carbon dioxide are transferred into and out of the blood in the lungs. The CO2 that leaves the body is produced with cell respiration, while the oxygen inside the blood, from the lungs, is used in cell respiration.

Anaerobic respiration vs Aerobic respiration

Both have the glycolysis reaction

Vary in:

• Whether oxygen is used (in anaerobic it isn’t)

• relative yields of ATP (in anaerobic it’s less)

• End products (aerobic respiration produces CO2 and water in both plants and animals)

• substrates (anaerobic uses only glucose)

• where the reaction finds place (anaerobic is only in the cytoplasm)

Variables affecting rate of cell respiration

• temperature and pH affect the functionality of the enzymes involved in the process

• availability of substrates, glucose and oxygen

• inhibitors for the enzymes in respiration

Measuring rate of cell respiration

The oxygen produced/consumed can be measured, e.g. with a manometer that measures the change in pressure

Phosphorylation

The addition of a phosphate group. E.g. the addition of a phosphate group to ADP to make ATP, in this case a condensation reaction

Decarboxylation

Removal of a carbon dioxide molecule. E.g. conversion of pyruvate into acetal CoA in aerobic respiration

Lysis

The splitting of a molecule. E.g. hydrolysis of ATP to ADP or macromolecules to monomers or glycolysis

Oxidation/Dehydrogenation

Oxidation is loss of an electron or loss of a hydrogen which is dehydrogenation

Reduction

Is the gain of electrons to a compound or addition of a hydrogen

Electron carriers

They temporarily accept and later release electrons or hydrogens

NADH/NAD+

Nicotinamide adenine dinucleotide - In cell respiration NAD is an electron carrier. NAD+ is oxidised and NADH is reduced

4 steps of aerobic cell respiration

Glycolysis, the link reaction, Kreb’s cycle and the electron transport chain

Simple word equation of aerobic respiration

Glucose (although this can be anything) + oxygen —> carbon dioxide + water + ATP

Glycolysis

Occurs in the cytoplasm

Glucose is phosphorylated into glucose biphosphate

Which is broken down (lysis) into two triose phosphate molecules

Which makes pyruvate (x2)

Total per glucose: 2 ATP and 2 NADH

The link reaction

Happens twice, with two pyruvates after glycolysis, occurs in the mitochondrial matrix

Decarboxylation and redox make acetyl co-enzyme A (2C), with the co-enzyme A (CoA) recycled from the Krebs cycle

Krebs cycle

Happens twice with 2 acetyl co-enzyme A per glucose, occurs in mitochondrial matrix

Oxaloacetate (4C) joins with acetyl co-enzyme A (2C) to make citrate (6 carbon molecule)

Citrate decarboxylises to a 5 carbon molecules

The 5 carbon molecule carboxylises and yields many reduced NADH and FADH2 to oxaloacetate (4C)

Repeat cycle

Total yield for Krebs cycle and link reaction

Per pyruvate (so x2 for per glucose)

1 ATP, 4 NADH, 1 FADH

and 3 carbon dioxide products

The electron chain

The electron carriers (NAD and FAD) are brought to the inner mitochondrial membrane and release their hydrogen ions and electrons by oxidation.

Electron carriers inside the membrane take the electrons and pump hydrogen ions into the intermembrane space to create a concentration gradient.

The protons (hydrogen ions) flow down their concentration gradient through an enzyme called ATP synthase. The enzyme makes ATP through a process called chemiosmosis.

Lipids in respiration

Lipids contain less oxygen than carbs and can produce more energy

Lipids have an energy yield per gram of 37 KJ whilst carbs have 17 KJ

Lipids don’t undergo glycolysis, so can not be used for anaerobic respiration

Anaerobic respiration

Cell respiration without oxygen, with only glycolysis as the end product pyruvate can be converted into lactate to regenerate NAD+

There is only a net yield of 2 ATP

Make lactate from pyruvate through a process called lactic fermentation.

Anaerobic respiration in yeast and plants

In plants/yeast, the pyruvate breaks down into ethanol and carbon dioxide which is known as ethanol fermentation.

In brewing, yeast is used to make ethanol and the other product carbon dioxide simply bubbles up through the liquid and is lost.

In baking, yeast is used so that the carbon dioxide bubbles make the dough rise. The ethanol is a waste product as it evaporates in the baking that follows.