Higher Human Biology Unit 1 – Human Cells Section 8 – Energy Systems in Muscle Cells

What can you remember? What are the three types of muscle tissue? Skeletal, cardiac and smooth What are the three types of muscle tissue? What are the products of anaerobic respiration in animal cells. Where does glycolysis take place What molecule donates its phosphate so that phosphorylation can take place? What gas is produced when 3 carbon pyruvate is converted into 2 carbon Acetyl CoA Lactate Cytoplasm ATP Carbon dioxide

Energy for Exercise Food is the source of energy for the human body and it also provides nutrients for growth and repair. When food is eaten, this is what happens…. The food is broken into soluble chemicals (e.g. glucose) by digestion in the gut. The soluble chemicals pass through the gut wall into the blood. The blood carries the soluble food chemicals to all of the body’s cells, where they will be used for

Substrates for Respiration Carbohydrates Starch and glycogen are made up of chains of glucose. This means that they can act as respiratory substrates since they can be broken down into glucose. Sucrose and maltose – these can be converted to glucose or intermediates Fats - These are broken down into glycerol and fatty acids Glycerol – converted to a glycolytic intermediate Fatty Acids – these are metabolised into metabolic fragments that enter the pathways as acetyl coenzyme A. Proteins These are broken down into amino acids by enzymes. These undergo deamination forming urea and respiratory intermediates.

Carbohydrates Starch (plants) and glycogen (animals) are made up of chains of glucose molecules. They can be broken down into glucose and used as a respiratory substrate

Fats When required, fat can be broken down into fatty acids and glycerol and be used as a respiratory substrate

Proteins Protein are composed of amino acids and are broken down in our diet Excess amino acids can be lost as urea or used as a respiratory substrate

a – Lactate Metabolism We will be learning to… Describe the process of lactate metabolism when muscle cells do not get enough oxygen to support the electron transport chain during strenuous exercise. State that pyruvate is converted to lactate Describe how this conversion involves the transfer of hydrogen from the NADH produced during glycolysis to pyruvate in order to produce lactate. State that this regenerates the NAD needed to maintain ATP production through glycolysis. State that lactate builds up and muscle fatigue occurs Describe how the oxygen debt is repaid when exercise is complete State that this allows respiration to provide the energy to convert lactate back to pyruvate and glucose in the liver.

Lactate Metabolism During vigorous exercise, the muscle cells do not get enough oxygen and the ATP only lasts a few seconds. Oxygen is needed for the citric cycle and the electron transport chain. Without the oxygen these stages do not occur Under these conditions pyruvate is converted to lactate. Only glycolysis is able to provide more ATP. It generates 2 ATP and 2 NADH from each molecule of glucose.

Glucose 2 NAD+ 2ADP +Pi Glycolysis 2ATP 2 NADH (net) 2 Pyruvate 2 NADH This conversion involves the transfer of hydrogen from the NADH produced during glycolysis to pyruvate in order to produce lactate. This regenerates the NAD needed to maintain ATP production through glycolysis. Glucose 2 NAD+ 2ADP +Pi Glycolysis 2ATP (net) 2 NADH 2 Pyruvate 2 NADH NAD+ Regeneration 2 NAD+ 2 Lactate

Oxygen Debt Lactate accumulates and muscle fatigue occurs. The oxygen debt is repaid when exercise is complete. This allows respiration to provide the energy to convert lactate back to pyruvate and glucose in the liver.

Lactate Metabolism Only glycolysis produces ATP (2 instead of 38) The pyruvate is converted into lactate Lactate can build up and cause fatigue and an oxygen debt builds up This process is reversible when at rest and more oxygen becomes available. The lactate is transported to the liver to be converted back to pyruvate. They are often used interchangeably to indicate the reduced form of NAD +  NAD+ . The overall reaction when oxidizing some molecule RH  2  RH2 is: RH  2 +NAD + ⟶NADH+H + +R RH2+NAD+⟶NADH+H++R . The proper reduced NAD +  NAD+ is NADH NADH (it accepts two electrons and one proton), but sometimes NADH  2  NADH2 is used to account for that second hydrogen that gets removed from the substrate being oxidized. The notation NADH  2  NADH2 doesn't really take into account the fact that the second hydrogen is charged, and not bound to the NAD NAD in the same way that the first hydrogen is, so it is confusing. The notation: "NADH+H +  NADH+H+ " is more correct and is also sometimes used.

b – Types of Skeletal Muscle We will be learning to… State that there are two types of skeletal muscle fibres. Describe the properties of slow-twitch muscle fibres State that they are useful for endurance activities Describe the properties of fast-twitch muscles State that they are useful for short periods of activity Explain that most human muscle tissue contains a mixture of both types of skeletal muscle Describe how athletes patterns of muscle fibres match their sport

Control of Muscle Fibres Muscle tissues work by exerting a force when they contract. This can be controlled by involuntary movements e.g. smooth muscle contractions of the heart chambers or voluntary contractions when parts of the skeleton is moved.

Types of Skeletal Muscle There are two types of skeletal muscle fibres. Fast Twitch Slow Twitch

Slow-twitch Muscle Fibres Slow twitch muscle fibres contract relatively slowly, but can sustain contractions for longer. They are useful for endurance activities such as rowing, long distance running, cycling or cross-country skiing Slow twitch muscle fibres rely on aerobic respiration to generate ATP and have many mitochondria, a large blood supply and a high concentration of the oxygen storing protein myoglobin. The major storage fuel of slow twitch muscle fibres is fats.

Myoglobin Myoglobin is an oxygen-storing protein present in muscle cells. It has a stronger affinity for oxygen than haemoglobin. This means that the oxygen has a higher chance of binding with myoglobin than haemoglobin. Due to this high affinity myoglobin is able to extract oxygen from blood for use by muscle cells, especially those in slow-twitch muscle fibres

Fast-twitch Muscle Fibres Fast twitch muscle fibres contract relatively quickly, over short periods. They are useful for activities such as sprinting or weightlifting Fast twitch muscle fibres can generate ATP through glycolysis only and have fewer mitochondria and a lower blood supply compared to slow twitch muscle fibres. The major storage fuel of fast twitch muscle fibres is glycogen.

Most human muscle tissue contains a mixture of both slow and fast twitch muscle fibres. This is genetically determined. Athletes show distinct patterns of muscle fibres that reflect their sporting activities.

Skeletal Muscle Fibres Physical activity requires parts of the body to move and is brought about by skeletal muscle fibres (either slow-twitch or fast-twitch). Skeletal muscles contain a genetically determined mixture of slow-twitch and fast-twitch fibres. In most muscles the ratio is balanced. However in other muscles one will dominate For example the back contains mainly slow-twitch muscles and the eyes mainly fast-twitch muscles

Feature Type 1 Slow-Twitch Type 2 Fast-Twitch Muscle contraction speed Slow Fast Length of time for which contraction lasts Long Short Speed at which fibre becomes fatigued Respiratory Pathways to make ATP Aerobic Respiration Glycolysis Number of mitochondria Many Few Blood supply Large Small Concentration of myoglobin in cells High concentration Low concentration Storage fuels used Fats Glycogen/Creatine phosphate Activities Long distance running, skiing Sprints, Weightlifting

Now I can….. a – Lactate Metabolism Describe the process of lactate metabolism when muscle cells do not get enough oxygen to support the electron transport chain during strenuous exercise. State that pyruvate is converted to lactate Describe how this conversion involves the transfer of hydrogen from the NADH produced during glycolysis to pyruvate in order to produce lactate. State that this regenerates the NAD needed to maintain ATP production through glycolysis. State that lactate builds up and muscle fatigue occurs Describe how the oxygen debt is repaid when exercise is complete State that this allows respiration to provide the energy to convert lactate back to pyruvate and glucose in the liver.

Now I can….. State that there are two types of skeletal muscle fibres. b – Types of Skeletal Muscle State that there are two types of skeletal muscle fibres. Describe the properties of slow-twitch muscle fibres State that they are useful for endurance activities Describe the properties of fast-twitch muscles State that they are useful for short periods of activity Explain that most human muscle tissue contains a mixture of both types of skeletal muscle Describe how athletes patterns of muscle fibres match their sport

CfE HH Biology 2017 A Q7 C

CfE HH Biology 2016 A Q9 B

CfE HH Biology 2015 A Q8 D

Word Definition Fast-twitch fibre type of muscle fibre used in short bursts of activity Lactate produced by the fermentation of pyruvate in mammalian muscle cells Muscle Fatigue painful condition caused by the accumulation of lactic acid in the muscles Myoglobin protein in muscle tissue that can bind with oxygen Oxygen Debt builds up during fermentation in the muscle cells Skeletal Muscle muscle attached to the skeleton that brings about locomotion Slow-twitch fibre type of muscle fibre used in endurance activities