Respiration

Question 1

Why do living organisms need to respire

Answer 1

-respiration is process that occurs in living cells and released energy stored in organic molecules
-the energy is immediately used to synthesise molecules of ATP from ADP and inorganic phosphate (Pi)
-ATP in cells can be hydrolysed to release energy needed to drive biological processes
-microorganisms (both prokaryotes and eukaryotes), plants, animals, fungi and protoctists all respire to obtain energy

Question 2

Why do living organisms need energy

Answer 2

-energy is the capacity to do work
-the energy that is stored in complex organism molecules - e.g. fats, proteins, carbohydrates - is potential energy
-it is also chemical energy converted from light energy during process of photosynthesis
-when this energy is released from organic molecules via respiration, it can be used to make ATP to drive biological processes:
-active transport
-endocytosis/exocytosis
-activation chemicals
-cell division
-DNA replication etc

Question 3

Describe the different metabolic reactions

Answer 3

-anabolic reactions are metabolic reactions where large molecules are synthesised from smaller molecules
-catabolic reactions are metabolic reactions involving hydrolysis of large molecules to smaller ones

Question 4

Importance of kinetic energy

Answer 4

-within living cells atoms, ions and molecules have kinetic energy and this allows them to move
-for example when molecules diffuse down concentration gradient, moving from one place to another, they use kinetic energy to do so

Question 5

Describe the structure of ATP

Answer 5

-ATP is standard intermediary between energy-releasing and energy-consuming metabolic reactions in both eukaryotic and prokaryotic cells
-structure of ATP is phosphorylated nucleotide
-each molecule of ATP consists of adenosine, which is the nitrogenous base adenine plus five-carbon sugar ribose and three phosphate (phosphoryl) groups

Question 6

Describe ATP in solution

Answer 6

-ATP is relatively stable (it does not break down ADP and Pi) when in solution but is readily hydrolysed by enzyme catalysis
-However, whilst in solution, it can easily be moved from place to place within a cell

Question 7

How efficient is the release of ATP

Answer 7

-energy-releasing hydrolysis of ATP is coupled with an energy-consuming metabolic reaction
-when ATP is hydrolysed to ADP and Pi a small quantity of energy is released for use in cells
-cells can therefore obtain energy they need for process in small manageable amounts that will not cause damage or be wasteful
-ATP is referred to as universal energy currency as it occurs in all living cells and is source of energy that can be used by cells in small amounts

Question 8

Describe the release of ATP as heat

Answer 8

-some energy is released from hydrolysis of ATP as heat
-the release of heat, both in respiration and during ATP hydrolysis, may appear to be inefficient and wasteful
-heat however helps keep living organisms ‘warm’ and enables their enzyme catalysed reactions to proceed at or near optimum rate

Question 9

What is glycolysis

Answer 9

-glycolysis is a biochemical pathway that occurs in cytoplasm of all living organisms that respire, including many prokaryotes
-the pathway involves a sequence of 10 reactions, each catalysed by a different enzyme, some with help of coenzyme NAD

Question 10

What are the three main stages of glycolysis

Answer 10

1) phosphorylation of glucose to hexose biphosphate
2)splitting each hexose biphosphate molecules into two triose phosphate molecules
3)
oxidation of triose phosphate to pyruvate

Question 11

What is NAD

Answer 11

-enzymes that catalyse oxidation and reduction reactions need help of coenzymes that accept hydrogen atoms removed during oxidation
-NAD is non protein molecule that helps dehydrogenase enzymes to carry out oxidation reactions
-NAD oxidises substrate molecules during glycolysis, the link reaction and Krebs cycle

Question 12

How is NAD made

Answer 12

-NAD is synthesised in living cells from nicotinamide (B3 vitamin) , the five-carbon sugar ribose, the nucleotide base adenine and two phosphoryl groups
-the nicotinamide ring can accept two hydrogen atoms, becoming reduced NAD

Question 13

Role of reduced NAD

Answer 13

-reduced NAD carries the protons and electrons to cristae of mitochondria and delivers them to be used in oxidative phosphorylation for generation of ATP from ADP and Pi
-when reduced NAD gives up the protons and electrons that it accepted during one of first three stages of respiration, it becomes oxidised and can be reused to oxidise more substrate, in process, becoming reduced again

Question 14

Describe the process of phosphorylation

Answer 14

-glucose is a hexose sugar which means it contains 6 carbon atoms
-it molecules are stable and need to be activated before they can be split into two three carbon compounds
1) one molecule of ATP is hydrolysed and released phosphoryl group is added to glucose to make hexose monophosphate
2) another molecule of ATP is hydrolysed and the phosphoryl group added to the hexose phosphate to form a molecules of hexose biphosphate. This sugar has one phosphate group at carbon atom number one and another at carbon atom six
-the energy from hydrolysed ATP molecules activates hexose sugar and prevents it from being transported out of cell

Question 15

Describe the splitting of the hexose biphosphate

Answer 15

-each molecule of hexose biphosphate is split into two three-carbon molecules, triose phosphate, each with a phosphate group attached

Question 16

Describe the oxidation of triose phosphate to pyruvate

Answer 16

-although this process is anaerobic, it involves oxidation, because it involves removal of hydrogen atoms from substrate molecules
1) dehydrogenase enzymes, added by coenzyme NAD, remove hydrogens from triose phosphate
2) two molecules of NAD accept hydrogen atoms and become reduced
3)at this stage of glycolysis, two molecules of NAD are reduced for every molecule of glucose undergoing this process. Also at this stage, four molecules of ATP are made for every two triose phosphate molecules undergoing oxidation

Question 17

What are the products of glycolysis

Answer 17

-from each molecule of glucose, at end of glycolysis there are
-two molecules of ATP: four have been made but two used to ‘kickstart’ process so net gain is two molecules of ATP
-two molecules of reduced NAD
-two molecules of pyruvate

Question 18

What are the four main stages of respiration

Answer 18

1)glycolysis
2)link reaction
3)Krebs cycle
4) oxidative phosphorylation
-the last three stages only take place under aerobic conditions
-under aerobic conditions pyruvate molecules from glycolysis are actively transported into mitochondria for link reaction
-in absence of oxygen pyruvate converted in the cytoplasm to lactate or ethanol
-in process, reduced NAD molecules are reoxidised so glycolysis can continue to run, generating two molecules of ATP for every glucose molecule metabolised