Week 12 - Nutrition and Metabolilsm Flashcards
Metabolism
Sum of body’s chemical reactions. Series of enzyme-catalysed reactions, which include 4 basic processes
- Harnessing energy: in chemical bonds of molecules obtained from diet (nutrients); may be used to make adenosine triphosphate (ATP)
- Converting: one type of molecule into another for cell’s synthesis reactions
- Synthesising macromolecules: such as proteins, polysaccharides, nucleic acids, and lipids
- Breaking down macromolecules: into monomers or other smaller molecules
Catabolism
- group of reactions where one substance is broken down into smaller parts
- EXERGONIC reactions, which releases energy
- cells can harness the energy released to drive other processes
- energy released by catabolic processes in the form of ATP
Anabolism
- group of reactions which case smaller molecules to be combined to make a larger molecule
- ENDERGONIC reactions (USE energy)
Metabolic rate
- total amount of energy expended by body to power all of its processes
- sum of all anabolic and catabolic reactions occurring in the body
Basal metabolic rate (BMR)
- The body continues to use energy even when at rest. BMR is the minimal rate of metabolism for an awake individual at rest
Resting conditions:
- person has not eaten for the past 12 hours and has had a restful night of sleep
- person is not performing physical activity and has not performed strenuous physical activity for at least 1hr
- person is not under physical or emotional stress
- temp surrounding person is constant and comfortable
Factors affecting total Metabolic rate and BMR
- pregnancy, anxiety, fever, eating, thyroid hormones, depression
- BMr varies between individuals, depending on factors such as gender and muscle mass ( skeletal muscle is a highly metabolically active tissue)
Metabolic reactions - energy requirements
- energy is released from exergonic CATABOLIC REACTIONS
- this energy can be used to SYNTHESISE ATP
- when ATP is broken down, energy is released and is used to fuel endergonic ANABOLIC REACTIONS
NUTRIENTS
A molecule obtained from food that body requires for its metabolic processes
WATER- essential component for multiple metabolic processes in body. broken down by enzymes through HYDROLYSIS
MACRONUTRIENTS - carbohydrates, proteins, lipids.
MICRONUTRIENTS- vitamins and minerals
Carbohydrates
45-65%
humans cannot digest fibre
Polysaccharides:
- starch
- glycogen
- cellulose (fibre)
Disaccharides:
- lactose
- maltose
- sucrose
Monosaccharides:
- glucose
- galactose
- fructose
Lipids
in diet includes triglycerides, cholesterol, certain vitamins
- Fats, mostly unsaturated =30% daily intake
- saturated fatty acids: mostly animal-derived products
- unsaturated fatty acids: commonly found in plant- derived products
- essential fatty acids: body is unable to sunthesize → must come from diet
Proteins
Proteins & 20 amino acids
- 10-35% of daily intake is from protein-rich food
- 11 nonessential amino acids : can be synthesised
- 9 essential amino acids: must be obtained from dietary sources
Vitamins
Fat-soluble: hydrophobic compounds, structurally similar to cholesterol → Vit A, D, E & K
Water-soluble: hydrophilic compounds featuring polar covalent bonds → Vit C & B
Minerals
any element other than carbon, hydrogen, oxygen and nitrogen that is required by living organisms
- 7 major minerals are ions (in moderate amounts_ → calcium, chloride, magnesium, phosphorus, potassium, sodium and sulfur
10 trace minerals are ions (v small amounts) →iodine, iron & selenium
ATP synthesis
- cells harness ATP energy by removing the 3rd phosphate group in a HYDROLYSIS reaction, bond between 2nd and 3rd is broken w/ a water molecule, releasing free phosphate and ADP (adenosine diphosphate)
ATP phosphorylation
Process where released energy can by used by a cell
process where ATP donates a phosphate group to a reactant → reactant becomes more reactive →favours conversion of reactant to desired product
Nutrients and ATP synthesis
- carbohydrates (glucose and glycogen) is the preferred source for ATP production
- breaking down glucose is a catabolic process known as GLYCOLYSIS resulting in the product PYRUVATE
- if carbohydrates in the diet do not meet metabolic demands for glucose, the body can produce glucose through non-carn sources → amino acids (proteins) & fatty acids (lipids)
- pyruvate can be used in the CITRIC ACID CYCLE (Kreb cycle) and the ELECTRON TRANSPORT CHAIN to yield more ATP molecules
Stores and function of carbohydrates
- Stored in
1. muscle glycogen
2. liver glycogen
3. blood glucose - Most carbohydrate serves as FUEL for the body (ATP SYNTHESIS)
→Neurons, RBCs and kidneys depend on glucose - Sugars also serve as STRUCTURAL COMPONENTS
→ nucleic acids, glycoproteins and glycolipids, ATP
regulation of blood glucose levels - rise
Stimulus: BGL rises after carb rich meal
→beta cells of pancreas release insulin into the blood
→ body cells take up more glucose & liver takes up glucose and stores it as glycogen
→ BGL declines
→ Homeostasis: BGL (70-110 mg/100ml)
regulation of blood glucose levels- fall
Stimulus: BGL falls after skipping meal
→ alpha cells of pancreas release glucagon into blood
→ liver breaks down glycogen and releases glucose into blood
→BGL rises
Homeostasis: BGL (70/110mg/100ml)
Carbohydrates absorption
- starts in oral cavilty when SALIVARY AMYLASE until pH drops to <4.5 in stomach
- final steps in carbohydrate metabolism in the small intestine:
→secretion of PANCREATIC AMYLASE
→ a number of enzymes from brush border of the small intestine breakdown carbohydrate into monosaccharides - in the liver excess glucose is stored as GLYCOGEN
Glucose as a primary energy source
- glucose is a small, soluble molecule that is easily distributed through body fluids
- glycolysis provides a small amount of ATP ANAEROBICALLY
- unlike ATP, glucose can be efficiently stored as GLYCOGEN
- the break down of glycogen (GLYCOGENOLYSIS) occurs v quickly and involves only a single enzymatic step. mobilisation of other intracellular reserves involves much more complex pathways and takes considerable more time
Glycolysis
- GLYCOLYSIs glucose is broken down in a series of 10 enzyme-orchestrated reactions that takes place in cytosol of all cells
- glucose is SPLIT into two 3-carbon sugar molecules called PYRUVATE
- the 10 reactions which take place dyring glycolysis can be condensed into two phases
1, energy investment phase
2. energy pay off phase
Glycolysis - first phosphorylation
Reaction 1
glucose is phosphorylated by ATP, yielding glucose-6-phosphate and ADP
Glycolysis - second phosphorylation
Reaction 2&3
- the carbon atoms in glucose -6-phosphate are rearranged and the molecule is then phosphorylated by another ATP, yielding fructose-1,6-biphosphate and ADP
Glycolysis - Cleavage
Reactions 4&5
- the six carbon fructose-1,6-biphosphate is split, and two three-carbon molecules are formed
Glycolysis - oxidation
reaction 6&7
- Glyceraldehyde-3-phosphate is phosphorylated and oxidised by NAD+ to hield NADH and 1,3-byphosphoglycerate, which then donates a Pi to ADP, producing ATP
Glycolysis - ATP synthesis
Reaction 8-10
- the carbon atoms in 3-phosphoglycerate are rearranged to form phosphoenolpyruvate, which donates a Pi to ADP, yielding ATP and pyruvate
Citric acid cycle (krebs)
2nd part of glucose metabolism
- Citrate synthesis: Acetyl-CoA combines with oxaloacate to form citrate and CoA (reaction 1)
- First oxidation: citrate is rearranged, then oxidized by NAD+ generating CO2 and NADH (reactio 2-4)
- ATP synthesis: succinyl-Coa is converted to succinate and CoA, while forming ATP (reaction 5)
- Second oxidation: succinate is oxidised by FAD and NAD+, generatinf FADH2 and NADH, and is converted back to oxaloacetate (reaction 6-8)
Protein function
- muscle contraction:movement of body, cells, cell structures
- cell membranes (receptors, cell identity, pumps)
- fibrous proteins (collagen, keratin): structural
- globular proteins (antibodies, myoglobin, enzymes) : functional
- plasma proteins: blood osmolarity and viscosity
protein absorption
In stomach:
- HCL denatures and unfolds proteins preparing them for easier chemical digestion, PEPSIN breaks proteins into small peptides
In Duodenum:
- PANCREATIC ENZYMES (trypsin, chymotrypsin and carboxypeptidase) continue breaking proteins into small peptides
In jejunum and ileum of small intestine:
- various PEPTIDASE ENZYME in intestinal lining brush border finish digestio of peptides into amino acids
amino acid catbolism
Dietary proteins are broken down into amino acid subunits in digestive tract; absorbed into bloodstream and delivered to liver
- AA consist of a carbon skeleton bound to a nitrogen containing amino group
- nitrogen is not used for energy so amino group is removed by TRANSAMINATION and the remaining carbon skeleton can be oxidised for fuel
Lipids - sources and finctions
- adipose tissue: helps protect tissues and organs and also provides fuel source
- plasma membrane and myelin sheath: composed of phospholipids and cholesterol
- cholesterol: precursor of steroids, bile salts and VIT D
- fatty acids: precursor of prostaglandins and other eicosanoids
- fat-soluble vits (ADEK)
Lipid absorption
- Begins in mouth with inguale LIPASE breaking down triglycerides into monoglycerides and fatty acids. continues in the stomach
- BILE SALTS from gallbladder emulsifies the large lipid droplet into smaller ones → greater access of PANCREATIC LIPASE
- most fats exist as triglycerides which contain three long hydrocarbon chains (FATTY ACIDS) linked to a modified sugar, (GLYCEROL)
Cholesterol
lipid which is not oxidised for duel; important to many anabolic processes in body
- Modified to produce Vit D, steroid hormones and bile salts
- Important structural molecule in plasma membranes
Packaged along w/ other lipids and proteins into stucutres called lipoproteins → provide transportation for cholesterol and other lipids in bloodstream
lipoproteins
Hydrophobic so protein carriers needed for transport in blood; complexes of lipids and proteins in blood.
categorised into 4 groups by DENSITY. the more protein content to lipid = higher density
1. chylomicrons: used for transport of dietary lipids to adipose tissue
- v low-density (VLDLs): made in liver to transport triglycerides to all tissues; converted to LDLs after removal of some triglycerides
- Low-density (LDLs): remnants of VLDL; carry cholesterol to cells; after they give away cholesteral they are repackaged into VLDL in liver as they are rich in cholesteral ‘bad lipoproteins’
- High-density (HDLs): HDL remove excess cholesterol from peripheral tissues and transport to liver for disposal ‘good lipoproteins’
fatty acid catabolism, beta oxidation
LIPOLYSIS: enzyme-catalyzed process that liberates fatty acids and glycerol
- both fatty acids & glycerol can be used for energy generation, but overwhelming amount of energy is derived from fatty acid BETA OXIDATION
- glycerol is converted to clyceraldehyde-3-phosphate and enters glycolysis
- fatty acids are catabolides to acetyl-CoA by BETA OXIDATION and to KETONE BODIES by KETOGENESIS
Ketogenesis
- when body uses beta-oxidation of fats to make glucose, a by-product of incompletely oxidised fates is KETONES
- during extreme caloric restriction, carbohydrate restriction, or full starvation, liver begins to rapidly oxidise fatty acids for energy; leads to production of large quantities of ketone bodies
- ketone bodies cannot be further metabolised by liver cells to be appreciable amount enter bloodstream
- accumulation of ketone bodies in blood is cakked KETOSIS; can lead to a dangerous lowering of blood pH called KETOACIDOSIS
- people w/ diabetes who do not closely control BGL are at high risk of ketoacidosis. w/o insulin cells will switch fat oxidation for glucose production in order to meet metabolic demands
Metabolic absorptive state
occurs right after feeding and can last up to 4 hrs when ingested nutrients enter bloodstream
processes occur as nutrients are being absorbed from small intestine:
- OXIDATION: of nutrient molecules which provide energy to cells
- GLYCONEOGENESIS: stores excess glucose in skeletal muscle and hepatocytes
- LIPGENESIS: stores triglycerides in adipocytes and hepatocytes
- PROTEIN SYNTHESIS: provides structural materials for cells
Absorptive state regulation
pancreatic hormone INSULIN orchestrates many absorptive state processes
- Release of insulin is triggered by inc BGL
- oxidation of glucose, small amounts of AA & FA generates ATP for cells
- AA enter cells for protein synthesis; excess glucose enters muscle and liver cells and is stored by glycogenesis
- excess glucose, AA and FA are converted to triglycerides.
- lipgenesis stores triglycerides in adipocytes and hepatocytes
postabsorptive state
- body usually instate in late morning, late afternoon and most of night
- most body tissues switch from carbohydrate sources for energy to using FA ( stoed in adipose tissue)
processes in PAS:
- break down of proteins in muscle cells, releases glucogenic AA into blood
- KETOGENESIS in hepatocytes, converts fatty acids to ketone bodies and releases into blood
- GLUCONEOGENESIS & GLYCOGENOLYSIS in hepatocytes release glucose into blood → crucial for brain
- LIPOLYSIS in adipocytes releases fatty acids into blood
- oxidation of molecules such as Fa provides most cells w/ fuel
Pstabsorptive state regulation
Maintaining normal BGL is a challenge → gluvose enters blood from two major sources
- glycogen breakdown in liver
- gluconeogenesis using AA and glycerol
co-ordinated by:
- GLUCAGON: released from pancreas and stimulates glycogenolysis and gluconeogenesis in liver
- EPINEPHRINE: stimulates glycogenolysis in skeletal and cardiac muscle and liplysis in adipocytes
- GLUCOCORTICOIDS: stimulate mobilisation of lipid and protein reserves; enhanced by GH
- pancreatic hormone GLUCAGON released when BGL drops; triggers glycogenolysis & gluconeogenesis
neural regulation of feeding
Hypothalamus houses two nuclei that ontrol homeostatic variables associated w/ feeding
- SATIETY CENTRE: elicits feeling of fullness and inhibits desire to eat
- HUNGER CENTRE: (feeding centre)elicits feelings of hunger and stimulates desire to eat
endocrine regulation of feeding : long-term
primarily hormonal:
- LEPTIN: produced by adipocytes; stimulates satiety centre and inhibits neurons in hunger centre
- GHRELIN: produced by stomachl stimulates neurons in hunger centre to promote hunger
endocrine regulation of feeding: short term
can also inhibit or stimulate feeding
- INSULIN → decreases food intake
- feeding stretches stomach walls and initiates release of gastrointestinal hormones → both stimulate vagus nerve to indirectly suppress hunger centre
