Lesson 2: Metabolism

Metabolism

sum of all chemical reactions in the body

Catabolism

breakdown (exergonic —> releases energy)

• Happens when you’re hungry and your body needs to break down stored energy

Anabolism

Building (endergonic —> consumes energy)

• Happens after you eat a large meal; you build new energy stories

Oxidation

the removal of electrons from an atom or molecule

Reduction

the addition of electrons to a molecule

Describe carbohydrate catabolic reactions

• Glycolysis

  • glucose breakdown to produce ATP and pyruvate

• Glycogenolysis

  • Breakdown of glycogen into glucose

Describe carbohydrate anabolic reactions

• Gluconeogenesis

  • Formation of glucose from lipid or protein (ex. lactic acid, certain amino acids, glycerol)

• Glycogenesis

  • Creating glycogen from glucose

Monosaccharide vs. disaccharide

Monosaccharide has one sugar unit while disaccharide is two sugar units joined together by a chemical bond (always contains a glucose molecule)

Dehydration synthesis

Builds large polymers from small monomers by removing H2O

Hydrolysis

Break large polymers by adding H2O

What is glycogen

• Storage form of glucose

• Main polysaccharide

• Found in liver and skeletal muscles

• Body’s preferred storage form of glucose

Describe glycolysis (where, process, yield, etc) and what enzymes help control it’s rate

• Where: cytosol

• Process: splits a 6-carbon glucose molecule into two 3-carbon molecules of pyruvic acid

• Yield: rapid rate, low yield of two net ATP

• Can occur with or without oxygen

• Enzymes: Hexokinase and PFK help regulate glycolysis

Describe the roles of hexokinase, PFK, LDH, and PDH enzymes

• Hexokinase

  • conversion of glucose to G-6-P (step 1) in glycolysis

• PFK

  • plays a major role in regulating the rate of glycolysis

• LDH

  • converts pyruvate to lactate (when oxygen is missing)

• PDH

  • converts pyruvate to acetyl CoA

Describe formation of acetyl CoA

Pyruvic acid from glycolysis is converted into acetyl CoA inside the mitochondria before entering the krebs cycle

Describe the Krebs Cycle (where, when, process, yield, etc)

• Where: mitochondria

• When: when you need ATP and O2 is present

• Beginning products

  • Acetyl CoA

  • NAD+ and FAD

  • ADP

• End products

  • CO2, NADH, FADH2, ATP (two molecules total)

• Slow rate, high yield of ATP

• Oxygen dependent

• Runs twice (one for each acetyl coA molecule)

Describe the ETC (where, when, process, yield, etc)

• What: series of electron carriers in the mitochondria

• Each carrier in the chain is reduced as it picks up electrons and oxidized as it gives up electrons

• The electrons release energy used to form ATP

• This mechanism links chemical reactions with the pumping of hydrogen ions (chemiosmosis)

What does complete aerobic respiration of a single glucose molecule yield?

36-38 ATP

Compare lipid metabolism to glucose metabolism

Lipid metabolism yields more ATP (~400 ATP) but it’s a much slower process than glucose metabolism

Energy stores: Where is ATP stored and how much is available to use

• Tissues

• 1 kcal

Energy stores: Where is PC stored and how much is available to use

• Tissues

• 4 kcal

Energy stores: Where is CHO (carbs) stored and how much is available to use

• Serum glucose

  • 20 kcal

• Liver glycogen

  • 400 kcal

• muscle glycogen

  • 1500 kcal

Energy stores: Where are fats stored and how much is available to use

• Serum FFA

  • 7 kcal

• Serum triglycerides

  • 75 kcal

• Muscle triglycerides

  • 2500 kcal

• Adipose tissue

  • 80,000 kcal

*Body prefers to burn fats

Energy stores: Where is protein stored and how much is available to use

• Muscle

  • 30,000 kcal

*Body doesn’t usually use muscles to get energy

What is a triglyceride made out of and what is it for

• glycerol (backbone) + 3 fatty acids (tails)

• how we store fat in the body

What are the implications of lipids being nonpolar (hydrophobic)

• They don’t dissolve in water

• Because blood plasma is over 90% water, lipids are packaged with specialized proteins to create water-soluble carriers called lipoproteins

  • the liver and intestines package the lipids

Describe chylomicrons (a class of lipoprotein)

Transport fats from your diet to adipose tissue

Describe very-low-density lipoproteins (VLDLs) (a class of lipoprotein)

Transport triglycerides from hepatocytes (in the liver) to adipocytes (the fat cells of adipose tissue)

Describe low-density lipoproteins (LDLs) (a class of lipoprotein)

carry around 75% of the total cholesterol in blood and deliver it to cells

Describe high-density lipoproteins (HDLs) (a class of lipoprotein)

remove extra cholesterol from body cells and the blood and transport it to the liver for elimination

• Helps get rid of excess cholesterol

• Carries more protein than fat —> that’s why it’s high density

Explain lipid metabolism (energy production, energy storage, structural roles)

• Lipids can be broken down and oxidized and create ATP, but requires oxygen to be present

• When the body already has enough energy and doesn’t need lipids, they get stored in adipose tissue (fat cells) to be used later

• Some lipids are used as structural molecules or to synthesize other essential substances

Describe lipid catabolism (lipolysis) and its steps

• the process of splitting triglycerides into fatty acids and glycerol

  • Step 1: Triglyceride hydrolysis (break triglycerides into its fatty acid tails and glycerol backbone)'

  • Step 2: Beta oxidation (turning fatty acids into acetyl CoA)

Describe lipid anabolism (lipogenesis) and its steps

• the process of synthesizing (creating) lipids from glucose or amino acids

  • Occurs when individuals consume more calories than needed, creating fats

Characteristics of lipid metabolism (yield, rate, etc)

• High yield

• Slow rate

• Oxygen dependent

Describe when lipogenesis occurs, what hormone stimulates it, and what did the hormone do during glucose metabolism?

• when

  • Occurs when energy/calorie intake exceeds the body’s needs

• What hormone stimulates it

  • Insulin - Helps lower blood glucose by taking glucose from your blood into cells

• What did that hormone do during glucose metabolism

  • Insulin lowers blood sugar levels by transporting glucose into cells

Describe ketone bodies

• Ketone bodies are alternative energy molecules produced when the body breaks down fats (lipid catabolism) for fuel

• Turn extra acetyl CoA into another form of energy (ketone bodies)

  • Happens when your body has low carbs and high fat

• Created through two acetyl CoA molecules combining to form acetoacetic acid which is converted to beta-hydroxybutyric acid and acetone

• Heart and kidney prefer to use acetoacetic acid for ATP production over glucose

What is ketoacidosis

• High levels of blood ketones

• Results in abnormally low blood pH

What does fasting, starving, high fat/low carb diet result in

• Large production of ketone bodies because more acetyl CoA is being produced through beta oxidation

• sweet smell of ketone body acetone on breath

• Also occurs in diabetics

Describe the difference between essential and non-essential amino acids

• Essential: have to eat the because your body doesn’t produce them

• Non-essential: your body makes them

What are proteins made of and what is their conformation (shape)

• Proteins are made of amino acids

• They have three main groups attached

  • amino group (NH2)

  • acidic carboxyl group (COOH)

  • side chain (R group)

what makes protein metabolism different from carbs and fats, and what are amino acids used for

• Digested proteins are broken into amino acids which ARE NOT stored

• Instead, amino acids are oxidized to produce ATP or used to synthesize new proteins

We use proteins for…

• enzymes

• transportation (lipoproteins)

• antibodies

• clotting blood

• hormones

• muscle fibers

Describe protein catabolism

• yields amino acids which are converted to other amino acids, fatty acids, ketone bodies, or glucose

  • Cells oxidize amino acids to generate ATP via the Krebs cycle

  • <5% of energy in most cases

Describe protein anabolism

creates new proteins by bonding together amino acids on ribosomes

Describe primary structure of proteins

order of amino acids, connected by peptide bonds

Describe secondary structure of proteins

twisting and folding of neighboring amino acids, stabilized by hydrogen bonds

• Alpha helix or beta pleated sheet

Describe tertiary structure of proteins

• 3-D shape of polypeptide chain

• can have helix and/or pleated sheets

Describe quaternary structure

• arrangement of two or more polypeptide chains

What part of cellular respiration does amino acids affect?

• Affects many steps in the Krebs cycle

• So…. if you’re deficient in these, you may have trouble breaking down your fats and carbs

Does the post-absorptive state mean you’re fasted (hungry) or fed (full)?

Hungry; you’re relying on stored energy

Does the absorptive state mean you’re fasted (hungry) or fed (full)?

Full; you’re actively absorbing nutrients from your last meal

During the postabsorptive state, energy needs are met by fuels already in the body. What are they and what organs are they stored in?

• Carbs are stored in glycogen (in skeletal muscles, liver, etc)

• Fats are stored in triglycerides (in adipose tissue)

What are the steps of the body’s response during the post-absorptive state?

1. There is a drop in blood sugar, along with rising amino acid levels

2. Low glucose levels stimulate the alpha cells of the pancreas islets

3. The stimulation results in the body releasing glucagon since glucose levels are low

4. Glucagon stimulates two main organs

• Liver: Glucagon causes glycogenolysis (breakdown of glycogen) and gluconeogenesis (stimulates production of glucose)

• Adipose tissue: Glucagon causes fat to be broken down. This increases levels of fatty acids in the blood, which is used by tissue cells (glucose sparing)

5. Leads to increased levels of glucose (and insulin) in the blood plasma

Where does glycogenolysis occur and what are its main stimulating hormone(s)

• Occurs in the liver (in hepatocytes) and skeletal muscle fibers

• Hormones: Glucagon and epinephrine

Where does lipolysis occur and what are its main stimulating hormone(s)

• Occurs in adipocytes (in adipose tissue)

• Hormones: Epinephrine, norepinephrine, cortisol, IFG, thyroid hormones

Where does protein breakdown occur and what are its main stimulating hormone(s)

• Most body cells, but especially skeletal muscle fibers

• Hormone: cortisol

Where does gluconeogenesis occur and what are its main stimulating hormone(s)

• Hepatocytes (liver) and kidney cortex cells

• Hormones: glucagon and cortisol

What are the steps of the body’s response during the absorptive state?

1. There is an increase in blood sugar

2. Increased blood glucose stimulates the beta cells of the pancreatic islets

3. This leads to increased insulin levels in the blood

4. Insulin targets tissue cells in two main ways

• Amino acid handling: enhances the active transport of AA into tissue cells which causes protein synthesis

• Glucose handling: Enhances the facilitated diffusion of glucose into tissue cells. Once inside cells, glucose is used for cellular respiration, stored as fatty acids and glycerol, or stored as glycogen.

Where does facilitated diffusion of glucose into cells occur and what are its main stimulating hormone(s)

• most cells

• hormone: always on

Where does active transport of amino acids into cells occur and what are its main stimulating hormone(s)

• most cells

• hormone: insulin

Where does glycogenesis occur and what are its main stimulating hormone(s)

• liver and muscle cells

• hormone: insulin

Where does protein synthesis occur and what are its main stimulating hormone(s)

• all body cells

• hormone: insulin, thyroid hormones, and IGFs

Where does lipogenesis occur and what are its main stimulating hormone(s)

• adipose cells and hepatocytes (in liver)

• hormone: insulin