cellular metabolism

1

Human AnatomyHuman Anatomy

CELLULAR METABOLISMCELLULAR METABOLISM

Pavemedicine.comPavemedicine.com

46

Processes of the Digestive SystemProcesses of the Digestive System

Figure 14.11

47a

Control of Digestive ActivityControl of Digestive Activity

Mostly by reflexes via the parasympathetic division

Chemical and mechanical receptors trigger reflexes

47b


Stimuli include: Stretch of the organ pH of the contents Presence of breakdown products

47b


Reflexes include: Activation or inhibition of glandular

secretions Smooth muscle activity

55

Digestion and Absorption in the Digestion and Absorption in the StomachStomach

Proteases act on:

Pepsin –protein digestion

Rennin –milk protein digestion

Absorption of:

Water, alcohol and aspirin

57a

Digestion in the Small IntestineDigestion in the Small Intestine

Pancreatic enzymes provide… Complete digestion of starch

Amylase Other carbohydrases

About half protein digestion (trypsin, etc.)

57b

Digestion in the Small IntestineDigestion in the Small Intestine

Pancreatic enzymes, cont…

Fat digestion (lipase)

Nucleic acid digestion (nucleases)

Alkaline content neutralizes acidic chyme

58

Stimulation of the Release of Pancreatic Stimulation of the Release of Pancreatic JuiceJuice

Vagus nerve

Local hormones

Secretin

Cholecystokinin

Figure 14.15

59

Absorption in the Small IntestineAbsorption in the Small Intestine

Water

Products of digestion

Most molecules absorbed by active transport

Lipids absorbed by diffusion

Nutrients transported to the liver

63

NutritionNutrition Nutrient – substance used by the body

for growth, maintenance, and repair Categories of nutrients

Carbohydrates Lipids Proteins Vitamins Mineral Water

67

Cellular MetabolismCellular Metabolism

“All the chemical reactions necessary to maintain life”

Anabolism: a constructive process during which larger molecules are built from smaller ones

Usually involves condensation

AKA dehydration synthesis

67

Cellular Metabolism, con’t…Cellular Metabolism, con’t…

•Carbohydrates

•Monosaccharides = simple sugars

•Glucose, fructose

•Disaccharides = Combinations of monosaccharides, removal of water

•Sucrose, lactose, maltose

• Polysaccharides: usually polymers of glucose

•Starch, cellulose, chitin

67

Cellular Metabolism, con’t…Cellular Metabolism, con’t…•Lipids

•1 glycerol + 3 fatty acids neutral fat + 3 H2O

•These are triglycerides

•Further modifications produce:

•Phospholipids (cell membrane)

•glycolipids (cell membrane)

•Lipoproteins (cell membrane, blood)

67

Cellular Metabolism, con’t…Cellular Metabolism, con’t…•Proteins

•Two amino acids a dipeptide + H2O

•Covalent bond formed is a peptide bond

•Unique to proteins

•Polypeptides: 2-100 amino acids

•Protein: >100 amino acids

•Require additional modification to become functional

67


•Modification occurs on four levels

•Primary: string of amino acids

•Secondary: helix or “pleat” structures

•Tertiary: 3-D folding

•Quarternary: two or more 3-D proteins that act as a functional unit

•i.e., hemoglobin, collagen

67


•Recall from Chemistry: •Proteins each have a unique 3-D shape

•Shape determines function

•Loss of shape leads to loss of function

•“denaturing” proteins with heat, pH changes

67


•May be structural or functional

•Structural:

•Play a role in cellular architecture

•Collagen, fibrin, actin, myosin, etc.

•Functional:

•Play a role in cell metabolism

•Enzymes, neurotransmitters, antibodies, etc.

67

Cellular Metabolism, con’t…Cellular Metabolism, con’t…•Enzymes:

•Biological catalysts

•Highly specific for a substrate

•Substrate: substance upon which an enzyme acts

• i.e., peptidases act only on peptide bonds in small polypeptides

•Produced only in presence of substrate

67

Cellular Metabolism, con’t…Cellular Metabolism, con’t…

•Enzymes:

•Huge protein molecules

•Alter shape to conform to shape of substrate (“wrap around” effect)

•Average 1500/cell (>5000 in liver cells)

•Most require co-enzymes

67

Cellular Metabolism, con’t…Cellular Metabolism, con’t…•Enzymes:

•Recognize substrate by shape of binding site

•Serve to lower energy required for reaction to occur (activation energy)

•therefore speed up reactions

•Not changed or used up during reaction

67

Cellular Metabolism, con’t…Cellular Metabolism, con’t…•Co-Enzymes:

•Required to activate enzymes

•Facilitate enzymatic reactions

•May be a metal ion (Zn++, Cu++, Fe++)

•May be a vitamin

•Vitamins are co-enzymes

•Only function if “their” enzyme is available

Cellular Metabolism Catabolism: substances are broken down into molecules

“destructive” process

Large molecules broken down into smaller molecules

Usually by hydrolysis

“splitting with water”

Adds H2O back into molecule

Breaks covalent bonds

Cellular Metabolism Catabolism

Energy is released when bonds break

Reverse of dehydration synthesis (condensation)

Hydrolysis = chemical digestion

Occurs simultaneously (and continuously) with anabolism

Processes controlled by enzymes

Cellular Energy Cellular energy is chemical energy

Derived from breaking chemical bonds

~ ½ Energy is stored as ATP

~ ½ Energy is released as heat

Helps maintain body temperature

Enzymes control in the process

Cellular EnergyAll nutrient molecules are ultimately

degraded or converted to glucoseOnly glucose can be used to make

ATPOxidation: cellular process of

chemically breaking apart a glucose molecule to release energy

Cellular EnergyGlucose oxidation occurs in 2 phases

Anerobic metabolismOccurs in cytoplasmWithout oxygenAKA glycolysisSplits glucose into two 3-Carbon

molecules: pyruvate

Cellular EnergyGlycolysis

Process also produces 2 ATPsIn yeast, plant cells:

Pyruvate can undergo alcoholic fermentation

In bacteria, animal cells:Pyruvate can produce lactic acid

Cellular EnergyAerobic metabolism

Uses oxygenAKA Kreb’s Cycle or Citric Acid

cycle or Tricarboxylic Acid (TCA) Cycle

Occurs in mitochondriaMakes more ATP than anerobic

processes


CO2 and H2O are waste products

CO2:

Diffuses out of cellsDissolves in plasmaProduces HCO3

- in blood

Exhaled from lungs


H2O:

“metabolic” waterExhaled from lungs

Final products of glucose oxidation:CO2, H2O, ATP


For each molecule of glucose:2 ATP formed in glycolysis36 ATP formed in TCA cycleEnergy stored in phosphate

bondsA reversible reaction

Metabolic Pathways“A particular sequence of enzymatic

reactions” Such as glycolysis, TCA cycle

Carbohydrate pathwaysCarbos should comprise most of

our diet (~ 50% complex carbs)Used as a primary energy sourceProduce 4kcal/gm

Metabolic PathwaysCarbohydrate pathways

Excess carbs converted to energy storage formsGlycogen (muscle, liver)Adipose tissue (hips)Process is anabolism

Metabolic PathwaysLipid pathways

Metabolism controlled by liverShould comprise <30% of calories

in dietGet 9 kcal/gm (more ATP!)Must be degraded into glycerol,

fatty acids, then pyruvateA reversible catabolic process

Metabolic PathwaysProtein pathways

Proteins should comprise ~30% of diet

Get 4 kcal/gmCatabolism is more complex

Proteins contain nitrogen


Deamination: removal of nitrogen from amino acidsOccurs in liverNitrogen is converted to urea

A nitrogenous waste product

Sent to kidneys for excretion


After deamination: amino acid “skeleton” is

processed in TCA cycleMay produce CO2, H2O, ATP

May form glucose or fat


Glucose formed from amino acid skeletons may be re-converted to amino acids

“Essential” amino acids: Body cannot make theseMust obtain in the diet

Regulation of Metabolic Pathways

Enzyme “saturation”Too much substrate for number of

enzyme moleculesReaction rate cannot increaseA single enzyme can control an

entire metabolic pathway“rate limiting” enzyme

92b

Digestive System: DisordersDigestive System: Disorders

Ulcers: bacterial infection with H. pylori

Vomiting: controlled by center in medulla oblongata

Activity of tract slows in old age Fewer digestive juices Peristalsis slows Diverticulosis and cancer more common

92b

Digestive System: DisordersDigestive System: Disorders

IBS: irritable bowel syndrome Crohn’s disease (autoimmune) Constipation Diarrhea Colitis Colon polyps/cancers

cellular metabolism

Health & Medicine