Lecture 18: Metabolism & Nutrition Flashcards
what is metabolism
the totality of biochemical reactions taking place in the body
what are the two types of metabolic reactions
catabolism & anabolism (both coupled by ATP)
Anabolic reactions are synthesis reactions, catabolic reactions are decomposition reactions
describe catabolism
-Converts large molecules into smaller ones
-Breakdown of organic substrates releases energy used to synthesize ATP
describe anabolism
-Converts small molecules into larger ones
-Synthesis of new organic compounds is an “uphill” process that forms new
chemical bonds
what are the functions of anabolism
-Perform structural maintenance or repairs
-Support growth
-Produce secretions
-Store nutrient reserves
what are bioenergetics
Study of the flow of energy and its transformation from one form to another in
a cell
what are oxidation-reduction (redox) reactions
important in energy transfer
-Oxidation – Gain of O2 or loss of hydrogen or electrons from an atom or molecule
-Oxidized substances – lose electrons and energy
review slide 5
-Two coenzymes act as hydrogen/electron acceptors in oxidative pathways
-Reduction – Gain of hydrogen or electrons by a molecule or loss of O2
-Reduced substances – Gain hydrogen or electrons and energy
-Oxidase – O2 transfer
what is phosphorylation
addition of phosphate group to a molecule
-forms ATP
what are the three mechanisms ATP generation
- Substrate level phosphorylation: cytosol, mitochondrial matrix
- Oxidative Phosphorylation: inner mitochondrial membrane
- Photophosphorylation: plants, bacteria
what is substrate-level phosphorylation
-Addition of phosphate group directly to ADP from a phosphorylated substrates
-Occurs:
* Twice in glycolysis
* Once in Krebs cycle
what is oxidative phosphorylation
-Generation of ATP through transfer of electrons from NADH and FADH2 to O2: By a sequence of electron carriers within mitochondria
-Generates most of ATP (~90%) used by the body cells
-It is the basis for formation of water – 2H2 + O2 → 2H2O
review slide 10
what is carbohydrate metabolism
-Body tissues use carbs in form of glucose
-Body’s use of glucose depends on the needs of cells
-These needs include:
❑ ATP production
❑ Amino acid synthesis
❑ Glycogenesis
❑ Lipogenesis
what is cellular respiration and the four sets of reactions
oxidation of glucose to produce ATP
1. glycolysis
2. pyruvate oxidation
3. citric acid cycle
4. oxidative phosphorylation
what is glycolysis
Glycolysis = “splitting of sugar”
-Breaks down glucose into two molecules of pyruvate in 10-step pathway
-Occurs in cytosol and has two major phases:
* Energy investment phase (1st 5 steps)
* Energy payoff phase (last 5 steps)
Occurs whether or not O2 is present
what are the two phases of glycolysis
energy investment phase, and energy payoff phase
review the ten steps in glycolysis on slides 14 &15
review the ten steps in glycolysis on slides 14 &15
review the ten steps in glycolysis on slides 14 &15
what is the fate of pyruvic acid
- deficiency of O2 (anaerobic conditions): pyruvate is reduced to lactic acid
-tissues poorly vascularized and/or lack mitochondrion: cornea, RBCs, leukocytes, kidney medulla, testes - presence of O2 (aerobic conditions): pyruvic acid is converted to acetyl coenzyme A (acetyl-CoA)
describe the formation of acetyl CoA
- CO2 leaves
- NAD+ -> NADH + H+ (acetyl group)
- coenzyme A enters (making acetate)
what is the krebs cycle (citric acid cycle)
-Occurs in mitochondrial matrix
-Acetyl group in acetyl-CoA enters Krebs cycle to complete the break down of pyruvate to CO2
-Involves eight reaction steps
what are the 8 reaction steps of the krebs cycle
Step 1 ( Citrate Formation)
Step 2 ( Citrate Isomers Formation)
Step 3 ( Isocitrate decarboxylation and oxidation)
Step 4 ( Succinyl-CoA Formation)
Step 5 ( GTP Production)
Step 6 (Fumarate Formation)
Step 7 ( Malate Formation)
Step 8 (Oxaloacetate Formation)
what are the fate of the products in the krebs cycle
- NADH and FADH2 → ETC
- GTP → ATP via ADP
- CO2 → lungs for excretion
describe the electron transport chain (ETC)
-Made up of protein complexes in inner mitochondrial membrane
*Where key reactions of oxidative phosphorylation occur
-Protein complexes act as series of electron carriers from NADH and FADH2
*Each carrier is reduced by picking up electrons, and oxidized as it gives up
electrons
-ETC does not generate ATP directly
*It breaks the large free-energy transferred from NADH and FADH2 to O2 into smaller steps that release energy in manageable amounts
what is chemiosmosis
-Chemiosmosis involves the use of energy in a proton (H+)gradient to drive cellular work
-Energy released through ETC is used to pump proton (H+) from the mitochondrial matrix to the intermembrane space, generating a gradient→ proton-motive force
-H+ then flow down their concentration gradient back across the inner membrane, through ATP Synthase synthase
-ATP is generated using kinetic energy of
passing hydrogen ions
what are the electron carriers in the ETC
-Flavin mononucleotide (FMN) – derivative of riboflavin (vit B2)
-Cytochromes – heme group. Include cyt b, cyt c1, cyt c, cyt a, cyt a3
-Iron-sulfur centers
-Copper atoms
-Coenzyme Q
what is the action of proton pumps & ATP synthase (ETC)
Inside the inner mitochondrial membrane, the carriers are clustered into 3 complexes, each acting as a proton pump that expels H+
review slide 22
review slide 22
review slide 22
what is glycogenesis
-formation of glycogen from glucose
-stored in skeletal muscle fibers and hepatocytes
-stimulated by insulin scereted by pancreatic β-cells
what is glycogenolysis
-Breakdown of glycogen to reform glucose
-In times of glucose deprivation – strenuous
exercise, etc.
-Stimulated by glucagon secreted by pancreatic alpha cells
what is gluconeogenesis
-Formation of glucose from non-CHO sources – proteins, triglycerides, lactic acid and some amino acids
-In time of glycogen depletion: prolonged starvation/fasting
-Stimulated by cortisol, glucagon, and thyroid hormones
describe lipids in lipid metabolism
-Contain carbon, hydrogen, and oxygen
-Triglycerides – most abundant lipid in the body
-Most are nonpolar and hydrophobic
-Blood plasma is > 90% H2O, thus, lipids must be transported combined with proteins produced by the liver and intestines → lipoproteins
function of lipoproteins and the structure
-Function: Deliver lipids to cells, and clearance from blood of lipids
-Inner core: mostly triglycerides
-Outer shell: proteins, phospholipids, cholesterol
-Outer shell proteins: apoproteins (A,B,C,D,E)
what are the 4 classes of lipoproteins
- chylomicrons
- very-low-density lipoproteins (VLDLs)
- low-density lipoproteins (LDLs)
- high-density lipoproteins (HDLs)
describe chylomicrons
transport dietary (ingested) lipids to adipose tissue
describe very-low-density lipoproteins
transport triglycerides from hepatocytes to adipocytes
describe low-density lipoproteins
carry about 75% of total cholesterol in blood, deliver it to cells
excessive LDL-> fatty plaque-> CAD; “LDL cholesterol = bad cholesterol”
describe high-density lipoproteins (HDLs)
remove excess cholesterol from body cells and blood, transport it to the liver for elimination
low risk of CAD-> “good cholesterol”
what are the dietary sources of lipids
- Triglycerides (neutral fats) – most abundant form; Found in:
* Saturated fats – meat, dairy foods, tropical oils, or hydrogenated oils (trans fats)
* Unsaturated fats – seeds, nuts, olive oil, and most vegetable oils - Cholesterol – found in egg yolk, meats, organ meats, shellfish, and milk products,
* Hepatocytes makes ~85% cholesterol.
* Increase in total cholesterol levels are associated with a greater risk of CAD
* Exercise, diet, and certain drugs are used to reduce high cholesterol levels
why do our bodies store lipids
if no immediate need, stored in adipose tissue
-oxidized to produce ATP when need arises
describe the lipid storages
-Provides important energy reserves
-Can provide large amounts of ATP, but slowly
-Difficult for water-soluble enzymes to reach
what does our body transport and distribute lipids
-Cells require lipids to maintain plasma membranes
-Steroid hormones must reach target cells in many different tissues
what are steps 1-5 in lipid transport and distribution
- michelles are absorbed into intestinal mucosa where they are converted to chylomicrons
- intestinal cells secrete chylomicrons, which are absorbed into lacteals
- from the lacteals, the chylomicrons proceed within the lymphatic vessels and into the thoracic duct, and from there are distributed throughout the body
- lipoprotein lipase in the capillary endothelium breaks down the chylomicrons and releases fatty acids and monoglycerides into the interstitial fluid
- resting skeletal muscles absorb fatty acids and break then down for ATP production or storage as glycogen. adipocytes absorb fatty acids and use them to synthesize triglycerides for storage
what are steps 6-12 in lipid and lipoprotein transport & distribution
- the liver absorbs chylomicrons and creates LDLs and VLDLs. to make LDLs, triglycerides are removed from the chylomicrons, cholesterol is added, and the surface proteins are altered. VLDLs contain triglycerides manufactured by the liver, plus small amounts of phospholipids and cholesterol. some of the cholesterol is used. by the liver to synthesize bile salts; excess cholesterol is excreted in the bile
- VLDLs transport triglycerides from the liver to muscle and adipose tissue
- the LDLs enter the bloodstream and are delivered to peripheral tissues
- once in peripheral tissues, the LDLs are absorbed
- the cells exract the cholesterol and uses it in various ways
- the cholesterol not used by the cells re-enters the bloodstream. there it gets absorbed by high-density lipoproteins (HDLs)
- the HDLs return ot cholesterol to the liver, where it is extracted and packaged in new LDLs or excreted with bile salts in bile
what is beta oxidation
-A sequence of reactions inside mitochondria that breaks fatty acid molecules into 2-carbon fragments that generates acetyl CoA
-FAD and NAD+ are reduced
-Each step:
* Generates molecules of acetyl-CoA, NADH, and FADH2
* Leaves a shorter carbon chain bound to CoA
what are the 4 main steps in beta oxidation
- lysosomal enzymes break down triglycerides molecules into 1 glycerol molecule and 3 fatty acids
- in the cytosol, the glycerol is converted to pyruvate through the glycolysis pathway
- fatty acids are absorbed into the mitochondria
- an enzyme reaction then breaks off the first 2 carbons as acetyl-CoA while leaving a shorter fatty acid bound to the second molecule of coenzyme A
what is lipogenesis
- Formation of lipids in the body (glucose, aa). Cells can:
1. Use almost any organic substrate - because lipids, amino acids, and CHOs can be converted to acetyl-CoA
2. Glycerol - Synthesized from dihydroxyacetone phosphate (DHAP)
- An intermediate product of glycolysis and gluconeogenesis
- Nonessential fatty acids and steroids – synthesized from acetyl-CoA
- Essential fatty acids – cannot be synthesized in the body
- Must be consumed
