Nutrition and metabolism

Question 1

What is a nutrient

Answer 1

A nutrient is a substance in our food that our body’s able to use to help with cellular function. Also, maintenance and growth repair. This often occurs through providing energy like ATP or the building blocks needed in a cell to perform these processes.

Question 2

Glucose as a nutrient

Answer 2

Glucose (from carbohydrates) is used with the addition of oxygen to produce ATP in the mitochondria.

Primary energy source. Nervous system and red blood cells uses only glucose, some cells can use other sources if needed.

Question 3

Amino acids

Answer 3

Come from proteins, and are used to create new proteins needed in cells and create enzymes for catalysing chemical reactions within the body.

Amino acids can be used in numerous ways, such as creating new muscle tissue or the haemoglobin used in red blood cells, to carry oxygen around our body, in the bloodstream, to our cells. Iron is also a mineral used in the production of haemoglobin in red blood cells.

Used for structural materials such as keratin, collagen and elastin, and muscles. Also used for enzymes and hormones.

Question 4

Fats as a nutrient

Answer 4

Fats are the other major nutrient, and these can be used to form cell membranes. Which phospholipid bilayer stabilised by cholesterol, which is also a type of lipid. Fats and cholesterol can be used to create new substances as well, such as lipid-based hormones.

They are used to form the phospholipid membranes and myelin sheaths surrounding insulating neurons. Lipids are used in adipose tissues as fatty deposits that have multiple uses including providing a cushioning protective layer for organs, as insulation for the body against cold temperatures, and also as a store of readily available energy when needed. Lipids are used to create prostaglandins, which are immune regulatory molecules formed with linoleic acid and arachidonic acid. Prostaglandins play important roles in smooth muscle contraction and the inflammatory pathway. Lipids also help to absorb fat soluble vitamins from the digestive tract, including vitamins A, D and E. Cholesterol has two forms; low-density lipoproteins, or LDLs, and high density lipoproteins, or HDLs. HDLs are considered to be the good cholesterol and LDLs the bad cholesterol, with excesses increasing risk of heart attack and stroke. Balance is important as LDLs help deliver cholesterol to cells to perform vital functions such as stabilizing cell membranes or producing steroid hormones. It is important to note that cholesterol consumption should be kept to a minimum as the liver can produce 85% of what we actually require.

Question 5

Vitamins and minerals

Answer 5

In addition to these major nutrients, we also consume and absorb many vitamins and minerals. B vitamins such as folic acid or vitamin B9 are vital in the process of DNA and RNA replication and other functions. Vitamins A, C and E all function as antioxidants, which means they help prevent oxidation in cells, which is associated with cellular stress and free radical formation.

We rely on ingesting them through food and dietary sources to maintain homeostatic processes.

Question 6

Sodium and potassium

Answer 6

Vital for the production of nerve signals.

Question 7

Vitamin D and mineral calcium

Answer 7

Vital for the formation and maintenance of bones. Calcium is also vital for muscle contractions.

Question 8

Water

Answer 8

Water forms 70 percent of vessels (each cell) and it makes up the bulk of our blood volume with three out of five and a half litres of our blood being plasma, which is 92 percent water and interstitial fluid, which is the fluid surrounding cells.

Question 9

Minimum average of nutrients

Answer 9

To have enough glucose we need to consume at least 130 grams of carbohydrates per day. Carbohydrates make up 45 to 65% of our total daily nutrients.

Lipids, or fats, should make up 20% of the total nutrients we consume each day. We average more than 40%. Anything above what we actually need is converted to adipose tissue and stored, adding body volume and mass.

Protein requirements are variable, depending on factors such as age, size and metabolic rate. As a general rule of thumb we should be consuming about 0.8 grams of complete proteins per kilogram of body weight. So in a 70 kilogram adult that would be about 56 grams of complete protein.

Question 10

Dietary sources for carbohydrates

Answer 10

Dietary sources include starch, which are complex carbohydrates found in grains and vegetables, sugars which are found in fruits, sugar cane, honey and milk, carbohydrates also come in the form of fibre which helps to maintain good health. Insoluble fibre, like cellulose is found in many vegetables. Soluble fiber comes in the forms of things like pectins which are found in fruits like apples and citrus. The primary use for glucose and other monosaccharides is to make cellular energy in the form of ATP. Other monosaccharides, fructose and galactose, get converted into glucose by the liver.

Question 11

Dietary sources of protein

Answer 11

Complete proteins refers to meats, fish, eggs or dairy, or milk products, which individually contain all of the required amino acids. Legumes, soy, nuts and cereals do not contain all of the required amino acids individually but eaten together they will provide all of the amino acids needed. Dietary sources of protein includes eggs, meat, milk, fish and meats, all complete proteins, and legumes, nuts, and cereals.

Question 12

What are vitamins

Answer 12

Vitamins are organic compounds needed in very small amounts for growth and well-being. Unlike other nutrients, vitamins do not serve as an energy source or building blocks. Instead, they are important for helping the body use the other nutrients, meaning without vitamins all the carbohydrates, fats, proteins that we eat would be useless. Many vitamins work as coenzymes, or enzyme helpers, which act with an enzyme to accomplish a particular chemical task. Many B vitamins are used as coenzymes for glucose oxidation into energy.

Question 13

Sources of vitamins

Answer 13

Most of our vitamins are not made in the body so we must ingest them in food or vitamin supplements. The exceptions to this are vitamin D, some B vitamins, vitamin K and vitamin A. Vitamin D is made in the skin upon exposure to sunlight. Some B vitamins, in particular B12, and vitamin K are synthesized by the intestinal bacteria in the large intestine. We can also convert beta-carotene, the orange pigment found in carrots and other foods, into vitamin A.

Question 14

Water soluble vitamins

Answer 14

Water soluble vitamins, which are the B complex vitamins and vitamin C, are able to be absorbed along with water from the GI tract. The exception to this is vitamin B12, which to be absorbed must be bound to intrinsic factor which is produced and released by cells in the stomach. Water soluble vitamins are not stored in the body for later use as cells take up what is required from the absorbed vitamins and whatever is left over will be excreted an hour or so later.

Question 15

Fat soluble vitamins

Answer 15

Fat soluble vitamins include vitamins A, D, E and K and bind to lipids in the gastrointestinal tract. They are absorbed with lipids. Anything that interferes with lipid absorption will interfere with the level of these vitamins, so it is important to be aware of this particularly using substances that prevent fat absorption. Fat soluble vitamins are stored in the body, except for vitamin K. An excess of these vitamins can be dangerous, in particular vitamin A overdoses have been well documented.

Question 16

Minerals in the body

Answer 16

The body requires moderate amounts of 7 minerals. These are calcium, phosphorus, potassium, sulfur, sodium, chlorine and magnesium. All other minerals are required in trace amounts. Some important ones include chromium, copper, zinc, manganese, iodine, selenium and molybdenum. Minerals, like vitamins, are not used to fuel the body but work with other nutrients to ensure homeostasis. Mineral uptake and excretion needs to be balanced to prevent toxicity. Minerals make up 4 percent of the body by weight, and calcium and phosphorus make up three-quarters of the total amount of minerals in the body. These minerals, along with magnesium salts, are responsible for hardening bones and teeth. Another important mineral is iron which is essential for haemoglobin function. It is required to move oxygen around the body.

Question 17

What is metabolism

Answer 17

All chemical reactions that occur in living organisms in order to maintain life.

Anabolic: synthesising, building, storing

Catabolic: decomposition, breaking

Question 18

Three stages of metabolism

Answer 18

1 Digestion:
dietary nutrients are digested and absorbed into the body

2 Storage and energy production:
Anabolism and catabolism occurring within the cell

3 Catabolism of energy:
Making ATP occurring in the mitochondria and requires oxygen to complete the breakdown of nutrients. Carbon dioxide and water are produced as by-products.

Question 19

Cellular respiration

Answer 19

Harvesting energy from nutrients, occurs in the cell (cytoplasm and mitochondria).

Completes process of catabolism of glucose.

Energy can be released by the oxidation of multiple fuel molecules and is stored as high energy carriers (NAD+ and FADH). These molecules store the energy released by the oxidation of fuel molecules. The energy released is in the form of electrons, which are negatively charged particles on atoms.

The reaction involved in respiration are catabolic reactions in metabolism.

Question 20

Glycolysis

Answer 20

Occurs in the cytoplasm of the cell.

Converts glucose (6 carbon molecule) into two 3 carbon molecules called pyruvate.

Conversion occurs over series of separate reactions/steps.

For each molecule of glucose that is converted into pyruvate, two ATP molecules are created.

The conversion of ADP, or adenosine diphosphate, to ATP involves phosphorylation, or addition of a phosphate molecule.

Question 21

The citric acid cycle

Answer 21

Citric Acid Cycle (CAC) = Tricarboxylic Acid Cycle (TAC)= Krebs cycle

Occurs in the mitochondria

It consists of a series of eight reactions that require enzymes

Oxidation of organic molecules derived from pyruvate

Acetyle CoA enters the cycle

Carbon from Acetyle CoA exits the cycle as CO2

Generates NADH and FADH2, very little ATP

Question 22

The electron transport chain

Answer 22

You may have noticed at this point that we haven’t generated much ATP. This figure represents how we generate more ATP in the electron transport chain, which is the next step in cellular respiration. The NADH and FADH2, which are the high energy electron carriers, pass through a series of proteins on the inner mitochondrial membrane, known as the electron transport chain which is part of the electron transport system. As they do this they are going to lose energy and will pump protons into the intermembrane space, which is the space between the inner and outer membranes of the mitochondria. The inner membrane is folded into cristae which houses the enzymes and coenzymes required for these reactions to occur. The hydrogen ions that are produced diffuse to ATP synthase where ATP is produced. Basically our electrons go from being high energy to low energy and oxygen accepts the low energy electrons. This is where we start to use the oxygen in the reaction shown earlier. The hydrogen and oxygen will form water and this is what drives aerobic respiration. You can see the complex process of the electron transport chain here, with the proton pumps embedded in the inner mitochondrial membrane. The breakdown of NADH and FADH2 to NAD+ and FAD, respectively, allows the movement of hydrogen ions or protons through the pumps in the membrane into the inner membrane space. At the same time the electrons from these high-energy electron carriers are transferred from complex to complex in the membrane with the result being more hydrogen ions being pumped into the space.

At the end you can see that the build-up of hydrogen ions in the inner membrane space increases the proton gradient on one side. This gradient is used by ATP synthase which harnesses the energy of the hydrogen ions as they move down the gradient back into the mitochondrial matrix. ATP synthase creates new ATP by joining an inorganic phosphate to an ADP molecule creating ATP. Overall the process of cellular respiration that utilizes glucose and oxygen and produces water, carbon dioxide and ATP can be summarized by this equation. The final outcome from cellular respiration, which is glycolysis, citric acid cycle and electron transport chain is the production of approximately 36 ATP from one glucose molecule.

Question 23

Summary

Answer 23

ATP is made in the cell’s mitochondria. Lots of ATP is made in the presence of O2 and glucose, and this process is known as aerobic respiration.

The waste products in the process are CO2 and H2O, which are removed from the body via the lungs and kidneys.

If O2 gas levels in the body are insufficient, anaerobic respiration commences. This process produces very little ATP, but produces the waste lactic acid.

This causes the muscles to cramp, and the lack of ATP results in the person feeling tired and lethargic.

Question 24

Aerobic vs Anaerobic

Answer 24

Complete catabolism of glucose needs O2, is aerobic

When there is insufficient oxygen present for complete catabolism of glucose, cells will undergo anaerobic respiration. Without oxygen, glycolysis occurs but pyruvic acid cannot enter the citric acid cycle or generate ATP from the electron transport chain. Glycolysis alone produces a small amount of ATP, net two molecules, and will still produce NADH and two pyruvic acid molecules. Without oxygen the pyruvate accepting the hydrogen ions from the NADH to create NAD+ is the only source of NAD+, which allows the glycolysis process to occur repeatedly to generate a small amount of ATP which is enough to keep us going until oxygen becomes available again. Pyruvate that doesn’t enter the citric acid cycle undergoes fermentation which results in the production of lactate, also known as lactic acid, which results in a buildup of lactic acid in the cells using this process.

Question 25

Glucose anabolism and blood glucose levels

Answer 25

ATP cannot be stored When glucose is available an oxygen present for it to be oxidized and catabolized fully then our cells will create as much ATP as possible. Glucose that is surplus to requirements will be stored as glycogen. Once glycogen storage capacity is reached any extra glucose is then stored as fat. The generation of glycogen from glucose is called glycogenesis. The use and storage of glucose is regulated by the endocrine system and the release of insulin and glucagon from the pancreas. Normal blood glucose is four to six millimoles per litre, but this will fluctuate throughout the day depending on the intake of glucose or level of activity. These fluctuations stimulate the release of insulin when blood glucose increases and glucagon when blood glucose decreases.

Question 26

Fed state

Answer 26

In a fed state, for example following consumption of food, blood glucose will increase from normal or homeostatic level. In this case we may have consumed a delicious Mars bar and absorbed all of the glucose from it. The glucose enters our bloodstream causing a spike in blood glucose levels signalling the pancreatic islet cells to release insulin. Insulin works like a key for glucose uptake in cells and without it cells would not be able to access the glucose and use it to make energy. Insulin also works to promote the storage of glucose as glycogen and also as fat in adipose tissue. In response to insulin blood glucose levels will decrease back towards normal, reducing the levels of circulating insulin. Negative feedback is used to stop the release of insulin from the pancreas.

Question 27

Fasted state

Answer 27

In a fasted state, such as between meals, during exercise or after sleep, blood glucose levels will decrease. A decrease in blood glucose will trigger the release of glucagon from the pancreatic islet cells, or alpha cells. Glucagon stimulates the release of glucose from glycogen stores into the blood to increase blood glucose. It also mobilizes fats from adipose tissue as well allowing glucose to be generated from fat through a process called gluconeogenesis, allowing conservation of glucose for organs that need it most such as neural organs. Amino acids can also be used to produce energy in the cells but this is only in extreme situations such as longer periods of fasting or some diseased states. It is preferable not to break down protein stores such as muscle into amino acids to be utilized for energy production. These processes contribute to increasing the blood glucose back into homeostatic range and through negative feedback again glucose levels will decrease.

Question 28

Glycogenolysis

Answer 28

Glycogenolysis is the release of glucose from glycogen and is the reverse process of glycogenesis. The enzyme glycogen phosphorylase acts to split the glycogen molecule back into glucose and phosphorylates these glucose molecules back into glucose one phosphate and then glucose 6-phosphate which can then undergo glycolysis.

Question 29

Gluconeogenesis

Answer 29

The other main process is gluconeogenesis which is a synthesis of glucose from fats and proteins, specifically amino acids. Gluconeogenesis occurs when too little glucose is available from other sources. This process is quite complicated with more steps and more waste products so it's not the ideal way to generate energy.

Question 30

Lipid metabolism

Answer 30

Lipid metabolism whilst it does produce waste products is a good source of energy for cells and is able to be stored in large quantities. In the fed state, or following a meal, lipogenesis occurs, which is the storage of lipids. Both unused fats from the diet and excess glucose will be stored in this way in our adipose tissue. In the fasting state lipolysis occurs, which is the breakdown of stored fats into glycerol and fatty acids and the use of these products in glycolysis to form ATP.

Question 31

Protein metabolism

Answer 31

Protein metabolism involves the use of amino acids, usually for synthesis of new proteins including enzymes. If essential amino acids are missing, meaning a specific protein can't be made and there are no amino acids available, or cells don't have enough glucose available, then amino acids can be used as an energy source. Cells can catabolize the amino acids in the process of gluconeogenesis allowing some glycolysis and ATP synthesis. The process involves the conversion of amino acids into pyruvic acid and then acetyl CoA, which can all enter the citric acid cycle and create some ATP. Ammonia is a waste product of amino acid catabolism however the liver is able to metabolize ammonia into urea that is excreted by the kidneys.

Question 32

Lipolysis

Answer 32

Lipid breakdown

Question 33

Nutrient that plays a role in metabolism by serving as a coenzyme

Answer 33

Vitamins

Question 34

Lipogenesis

Answer 34

Lipid synthesis

Question 35

Molecular fuel that cells need to make ATP

Answer 35

Glucose

Question 36

If glucose energy is not needed immediately it can be stored as what in muscles or liver?

Answer 36

Glycogen

Question 37

The molecule that cells use to drive anabolic reactions

Answer 37

ATP

Question 38

Anabolism includes reactions in which

Answer 38

larger molecules or structures are built from smaller ones.

Question 39

Catabolism involves processes that

Answer 39

break down complex structures to simpler ones.

Question 40

It is important to ensure that your diet is adequately rich in vitamins because:

Answer 40

most vitamins are coenzymes needed to help the body utilize essential nutrients.

Question 41

The molecule that serves as the major source of readily available body fuel is

Answer 41

Glucose

Question 42

The primary function of cellular respiration is to

Answer 42

generate ATP, which traps some of the chemical energy of food molecules in its high-energy bonds.

Question 43

Complete process

Answer 43

The nutrient pool within a cell includes all of the substrates in the cytoplasm that are available for anabolism catabolism. This pool includes Fatty acids, glucose and amino acids. Fatty acids can be anabolised to be stored as triglycerides. The breakdown of fatty acid releases glycerol and acetyl-CoA suitable for use by the mitochondria. Glucose can be anabolised via glycogenesis to be stored as glycogen. The release of glucose from glycogen is called glycogenolysis. When glucose is broken down into two three-carbon chains, this is called glycolysis. This is then further broken down to be used in the citric acid cycle in the mitochondria. In the process, organic molecules are broken down, carbon dioxide molecules are released, and hydrogen atoms are transferred to coenzymes that deliver them to the electron transport system. The primary use of amino acids is the synthesis of proteins, and so are seldom broken down if other energy sources are available.

Question 44

Energy consumption at rest can be estimated by monitoring oxygen utilisation. Explain why.

Answer 44

Energy use at rest is powered by mitochondrial energy production, and mitochondrial energy production is proportional to oxygen consumption.

Question 45

How does the body maintain stable blood glucose levels in fed (absorptive) and starved (post absorptive) states?

Answer 45

The fed or absorptive state, is approximately 4 hours in duration following a meal, when nutrient absorption is occurring. The starved, or post absorptive state, is when the body is not absorbing nutrients and so it relies on internal energy reserves to meet demands. During the absorptive state, insulin prevents a large surge in blood glucose after a meal by stimulating the liver to remove glucose from the circulation. During the post absorptive state, blood glucose begins to decline, triggering the release of glucose into the circulation.

Question 46

The nervous system needs a constant supply of glucose. What changes occur in cellular metabolism during the starved body state to meet this need?

Answer 46

During the starved state, other tissues shift to fatty acid or amino acid catabolism, conserving glucose for neural tissues.