Cell respiration

Question 1

Why is ATP a nucleotide?

Answer 1

Because it contains of: adenine, the 5 carbon sugar, ribose and 3 phosphate group (in a chain and negatively charged).

Question 2

What is ATP used for?

Answer 2

As temporary energy storage and for energy transfer between processes and between different parts of the cell.

Question 3

What properties of ATP make it suitable for its role?

Answer 3

• it’s soluble in water so it can move freely through the cytoplasm and other aqueous solutions in the cell.
• it’s stable at pH levels close to neutral, like the cytoplasm.
• it cannot pass freely through the phospholipid bilayer of membranes. This means it cannot diffuse out of a cell and its movement between membrane-bound organelles can be controlled.
• the 3rd phosphate group can easily be removed and reattached by hydrolysis and condensation reactions.
• hydrolyzing ATP and ADP and phosphate releases a relatively small amount of energy. This is enough for many processes in the cell. If more energy was released, there would often be excess. This would be wasted by conversion to heat.

Question 4

3 things cells need ATP for

Answer 4

• synthesizing macromolecules
• active transport
• movements

Question 5

Explain why synthesis of macromolecules need ATP

Answer 5

Anabolic reactions that link monomers together into polymers would be endothermic andtherefore unlikely to happen without coupling them to conversion of ATP to ADP.

One of more ATP molecules is used every time a monomer is linked to the growing polymer. Synthesis of DNA during replication, RNA in transcription and proteins in translation all require energy from ATP:

Question 6

Explain why ATP is required for active transport

Answer 6

Pumping ions or other particles across a membrane against the concentration gradient requires energy from ATP. The energy is used to cause reversible changes in the conformation (shape) of the pump protein. When the pump is in one conformation, the particle can enter it from one side of the membrane. When the pump is in the other conformation the particle can exit on the other side of the membrane. One of the two shapes is more stable than the other. ATP is used to cause the change from the more stable to the less stable confirmation. The change back to the more stable conformation happens without the need for energy.

Question 7

Explain why ATP is required for movements

Answer 7

Cells require energy from ATP for movement. Components of cells are moved, for example, chromosomes are moved to the poles during mitosis and vesicles move to transport within cells. Larger amounts of energy, and therefore ATP molecules are needed to change the shape of a cell, for example when dividing cell pinches apart during cytokinesis. Some cells use changes of shape for movement from place to place, for example, phagocytes in the human blood system move to sites of infection. Muscle cells can contract powerfully using large arrays of actin and myosin filaments, which exert force by sliding across each other. The energy for these movements is provided by ATP.

Question 8

Where can energy come from thats required to convert ADP and phosphate back to ATP

Answer 8

• cell respiration, in which energy is released by oxidizing carbohydrates, fats or proteins.
• photosynthesis,s in which light energy is converted to chemical energy.
• chemosynthesis, in which energy is released by oxiding inorganic substances such as sulfides

Question 9

What happens in cell respiration?

Answer 9

In cell respiration, carbon compounds are oxized to release energy and this energy is used to produce ATP:

Question 10

What carbon compounds are oxidized in cell respiration?

Answer 10

A wide range of carbon compounds can be used as respitory substrates, but glucose and fatty acids are the main ones in may cells.

In humans, the food we eat is the source of respiratory substrates.

Plants use carbohydrates or lipids previously made by photosynthesis.

Question 11

How does oxygen and carbon dioxide move across the plasma membrane?

Answer 11

Oxygen and carbon dioxide move across the plasma membrane independently by simple diffusion.

Question 12

What are gas exchange and cell respiration?

Answer 12

Interdependent

Question 13

Why is gas exchange and cell respiration interdependent?

Answer 13

Without gas exchange, cell respiration could not continue because there would soon be a lack of oxygen and a harmful excess of carbon dioxide inside the cell.

Without cell respiration, gas exchange could not continue because the use of oxygen and the production of carbon dioxide in respiration create the concentration gradients that cause the gases to diffuse.

Question 14

Two examples of metabolic pathways used in cell respiration

Answer 14

aerobic and anaerobic

Question 15

Contrast aerobic and anaerobic cell respiration

Answer 15

In aerobic respiration, oxygen is used as an electron receptors in oxidation reactions. In anaerobic, oxygen is not used, instead other substances act as oxygen acceptors in oxidation reactions.

In aerobic respiration, carbohydrates, such as glucose, lipids including fats, oils, and amino acids deamination can be used. In anaerobic only carbohydrates can be used.

In aerobic respiration carbon dioxide and water are waste products. In anaerobic, carbon dioxide plus either lactat or ethanol are the waste product, and water is not produced.

In aerobic respiration, the yield of ATP is much higher, more than 30 ATP molecules are produced per glucose. Whereas, anaerobic the yield of ATP is much lower, only 2 ATP molecules are produced per glucose.

In aerobic respiration, intial reactions are in the cytoplasm, but more occur in mitochondria including use of oxygen. In anaerobic respiration, all reactions occur in the cytoplasm, so the mitochondria is not required.

Question 16

Why do oxidation and reduction processes occur together?

Answer 16

Because they in they involve transfer of electrons from one substance to another.

Question 17

Role of NAD

Answer 17

It’s an electron carrier that can accepzs and lose electrons reversibly. They often link oxidation and reductions in cells.

Question 18

Explain how NAD becomes NADH

Answer 18

NAD initially has one positive charge, so it exists as NAD+. Substances are oxidized by removing two hydrogen atoms. Each hydrogen consists of an electron and a proton. NAD+ accepts two electrons and one proton from the hydrogen atoms, becoming NADH.

Question 19

First step in aerobic respiration

Answer 19

Glycolysis.

Question 20

Explain glycolysis

Answer 20

Glucose or another monosaccharide is the substrate. It happens in the cytoplasm of cells. In glycolysis, glucose is converted to pyruvate by a chain of reactions each of which is catalyzed by a different enzyme. A useful outcome of glycolysis is the production of a small yield of ATP without any oxygen being consumed. The 4 main steps in glycolysis is:
- phosphorylation of glucose
- lysis
- oxidation
- ATP formation

Question 21

Explain phosphorylation of glucose in glycolysis

Answer 21

Phosphorylation is the addition of phosphate to a molecule. This requires energy but makes a molecule more unstable and therefore more likely to participate in subsequent reactions. In cells, many phosphorylation are carried out by transfer of a phosphate from ATP. Below are the steps for phosphorylation of glucose:
- the glucose is turned into glucose-6-phosphate

• glucose is converted into fructose, creating a symmetrical molecule that can be split in half: glucose-6-phosphate –> fructose-6-phosphate
• there is done second phosphorylation: fructose-6-phosphate –> fructose-1,6-biphosphate

Question 22

Explain lysis in glycolysis

Answer 22

This is stage 2. The fructose biphosphate is now split into two molecules of triose phosphate, which can be seen below:
frusctose-1,6-biphosphate –> 2 triose phosphate

Question 23

Explain oxidation in glycolysis

Answer 23

This is stage 3. Each of these triose phpshate is oxidized by removing hydrogen. The hydrogen atoms are removed, not hydrogen ions. If hydrogen ions were moved, no electromns would have been lost by the triose phsohate, so it wpuldn’t have been oxidized.

The hydrogen is accepted by NAD, which becomes reduced NAD.

Oxidation of a sugar-produced group and the organic acid. In those case the sugar is triose with one phosphate group and the organic acid is glycerate carrying two phosphates. Energy is released by the oxidation of triose allows a second phosphate group to become attached to the product is biphosphoglycerate rather than phosphoglycerate.

triose phosphate + phosphate –> biphosphoglycertae

Question 24

Explain ATP formation

Answer 24

ATP is produced in the final reactions by glycolysis, by transfer of phosphate groups to ADP: This can happen twice because phosphoglycerate has two phosphates. In these reactions, the glycerate is converted to another organic acid, pyruvate.

Two biphosphoglycerate molecules are produced per glucose and each of them yields two ATPs. Four ATPs are produced per glucose in these final reactions of glycolysis.

Question 25

What are the overall outcomes of the 4 stages of glycolysis per glucose?

Answer 25

• one glucose contains 6 carbon atoms is converted into 2 pyruvates each containing 3 carbon atoms
• Two NAD molecules are converted to reduced NAD
• There’s a net yield of two ATPs. This is because two are used in the first stage of glycolysis and four are produced in the final stage, so the new yield is 2 per glucose. Although this is a relatively small yield, it doesn’t require oxygen. So, when oxygen supply is limited it’s useful.

Question 26

How is pyruvate converted into lactate?

Answer 26

Two hydrogen atoms are transferred to another molecule, oxidizing reduced NAD.

Hydrogen in transferred from reduced NAD to pyruvate converting it into lactate.

Answer 27

This is a two-stage process. In the first stage, carbon dioxide is removed from the pyruvate in a decarboxylation reaction The product is ethanol.

In the second stage, two hydrogens are transferred from reduced NAD to ethanol, converting it to ethanol.

The number of NADs regenerated is the same as the number used per glucose in glycolysis, so this process allows the production of ATP by anaerobic respiration to continue indefinitely, as long as glucose is available and ethanol concentrations do not rise too high.