bio 20 ch6 - digestive system

Negative Feedback

Negative Feedback

mechanism by which the body keeps a variable stable, maintaining homeostasis

Homeostasis

A tendency to maintain a balanced or constant internal state

3 Components of Negative Feedback & Homeostasis

1) Sensor - detects change in internal environment
2) Effector - brings condition back to normal
3) Control center - activates effector based on sensory info

For example, if your body temperature is too high, a negative feedback loop will act to bring it back down towards the set point, or target value.

Working Out & Sweating...

Working out --> Excessive Heat production --> Sensor --> Control center (brain) --> Effector (dilated blood vessels, increase sweat) --> Heat released --> Cool down--> Back to sensor

The cycle repeats

Macromolecules

Foods can be grouped into 4 major macromolecules:
<b>Macromolecules</b> - large, complex organic molecules

1) Carbohydrates
2) Lipids
3) Proteins
4) Nucleic Acid

How are macromolecules assembled/disassembled?

2 processes:
1) Dehydration synthesis
2) Hydrolysis

Dehydration Synthesis (pg207)

chemical reaction that BUILDS macromolecules

-2 smaller molecules are joined together by <b>removing</b> an H₂O (water) molecule
-Requires enzymes to speed up reaction
-"Anabolic" reaction (smaller --> larger)

A + B --> AB + H₂O

Hydrolysis (pg207)

-Large macromolecules BROKEN into smaller units by <b>adding</b> H₂O (water) molecules
-Requires enzymes
-"Catabolic" reaction (larger --> smaller)

AB + H₂O --> A + B

Carbohydrates

-Contain carbon, hydrogen, and oxygen (C:H:O) in a 1:2:1 ratio
-Produced by photosynthesis
-Main function: <b>Energy storage</b>

Two types:
1) Simple sugars
- a) monosaccharides
- b) disaccharides
2) Polysaccharides

Monosaccharides

-Simple sugars (mono = 1)
-<b>glucose</b>, <b>fructose</b>, <b>galactose</b> - all C₆H₁₂O₆

-Can have 3-7 C's i.e. trioses (3 C) or pentoses (5 C) - ribose, deoxyribose

Isomers

same molecular formula, different structures, so different chemical properties

Disaccharides

-2 monosaccharides joined together by dehydration synthesis

3 important ones:
Malt sugar - 1) <b>glucose</b> + <b>glucose</b> --> <b>maltose</b> + H₂o
Table sugar - 2) <b>glucose</b> + <b>fructose</b> --> <b>sucrose</b> + H₂o
Milk sugar - 3) <b>glucose</b> + <b>galactose</b> --> lactose + H₂o

C₆H₁₂O₆ + C₆H₁₂O₆ --> C₁₂H₂₂O₁₁ + H₂o

Polysaccharides

-many simple sugars combine. Ex. glycogen, starch, cellulose
a) <b>Glycogen</b> - storage form of carbs in ANIMALS
- in liver and muscle cells
- ~700 glucoses, branched
b) <b>Starch</b> - storage form of carbs in PLANTS
- 2 forms - amylose, amylopectin
- ~1100 glucoses
c) <b>Cellulose</b> - in plants
- insoluble "fibre," in plant cell walls
- ~3000 glucoses. We cannot digest it, lack enzymes

Lipids

Energy-rich organic compounds, such as fats, oils, and waxes, that are made of carbon, hydrogen, and oxygen.

C-H-O compounds
- Have higher energy bonds than carbs
- Non polar --> equal sharing of electrons
Functions: membrane structure (phospholipids), insulation, energy storage after carbs, some hormones (steroids)

Lipids structure

Glycerol + 3 fatty acids = triglyceride (dehydration synthesis)

Fatty acids can be:
<b>Saturated</b> = only single C-C bonds, maximum amount of H's making it very stable
<b>Unsaturated</b> = has double (C=C) or triple bonds (C=C), easier to break down

Proteins

- C, H, O & N, S
- Produced by ribosomes
- Most abundant organic molecule
- Functions : structural - membrane, hormones, enzymes, muscle components
- Energy is NOT a main function

Protein structure

-Structure: made of <b>chains of Amino Acids</b>
-There are 20 amino acids
> 9 essential (must eat them)
> 11 non-essential (body produces)
-"Peptide bond" joins amino acids
-"Polypeptide" = proteins

What makes one amino acid differ from another?

Amino acids differ from each other with respect to their <b>side chains</b>, which are referred to as <b>R groups</b>.
The R group for each of the amino acids will differ in structure, electrical charge, and polarity.

Nucleic Acids

-Mixtures of 4 nucleotides --> nitrogenous base, 5-C sugar and a phosphate group
-Form <b>DNA</b> and <b>RNA</b>
-Function: provides the instructions for protein synthesis, cell function/activity

Benedict's solution

tests for "reducing sugars" = monosaccharides & some disaccharides
blue ------> cloudy green, yellow, orange, red
(-) (+)

Iodine

tests for starch
yellow -----> blue/black
(-) (+)

Biuret

tests for proteins, binds to peptide bonds
Blue ------> purple
(-) (+)

Sudan IV

tests for lipids
insoluble black powder ----> dissolves to make red
(-) (+)

Translucence test

tests for lipids
no grease spot ----> grease spot
(-) (+)

Summary

Dehydration Synthesis:
3 fatty acids + glycerol ---> triglyceride + H₂o
AA + AA ----> polypeptide + H₂o
glucose + fructose ----> sucrose + H₂o

Hydrolysis:
lipid + H₂o ---> 3 fatty acids + glycerol
protein + H₂o ----> AAs
sucrose + H₂o ----> glucose + fructose

Other substances

Vitamins - help chemical reactions in body
- only a small amount required
- our body can make a few
Can be:
Fat soluble - stored in fat tissue, too much can be toxic, Ex. Vit A, D, E, K
Water soluble - dissolve in water, not stored in body (washed out), Ex. Vit C and B Complex

Enzymes

-<b>Protein catalysts</b> (speed up reaction)
-Lowers the <b>activation energy</b> (energy needed for reaction to occur), reactions occur faster
-Have specific "<b>substrates</b>" = molecules on which an enzyme works i.e. lactose --> lactose
-Have an active site on which substrate attaches
-Are reusable!! (do NOT get consumed)
-May be assisted by coenzymes (metals, vitamins) to help build substrates OR cofactors (organic materials from inorganic minerals)

Substrate

-the reactants
-only the correct substrate will fit on the active site

Active Site

-Site of highest surface area
-reaction occurs here

Enzyme

-the reactants achieve a lower activation energy as a result of the enzyme
-the enzyme is restored to its previous form after the reaction is complete

Factors that affect Reaction Rate

1) Temperature
2) pH
3) Substrate concentration
4) Competitive inhibitors
5) Non-competitive inhibitors

Temperature & pH

-have optimums --> high temps and extreme pH causes <b>denaturation/coagulation</b>

Substrate Concentration

-reactions occur faster with more substrate until max speed and concentration is reached

Competitive inhibitors

-molecules compete with substrate for active sites on enzyme, prevents substrate from attaching
*competes/interferes with substrate
e.g. - poisons, penicillin, cyanide

Non-competitive inhibitors

-inhibitor does NOT attach on active site, but somewhere else called the "<b>allosteric site</b>", changing the shape of the enzyme... preventing the enzyme from working with substrate!

An inhibitor binds to a secondary site on the enzyme. This changes the shape of the active site and and prevents the substrate from binding

In biological systems, the <b>competitive inhibitor is often the</b>...

<b>end product of the enzymatic reaction</b>. As more end product is created and binds to the active site, enzyme activity is inhibited. That's a <b>negative feedback loop</b>!

The Digestive System

Breaks down food into absorbable units that enter the blood for distribution to body cells. A series of hollow organs joined in long twisting tube from the mouth to anus.

Ingestion

Intake of food

Digestion

Breakdown of food substances into simpler forms that can be absorbed and used

2 ways of Digestion

1) Physical breakdown - ex. teeth
2) Chemical breakdown - ex. saliva

Egestion

removal of undigested waste

Mouth & Esophagus

first step in digestion, with mechanical breakdown and breakdown of carbs with alpha-amylase

pH in mouth is

7

Tongue

-mechanical (physical) digestion
-Contains taste buds
-Mixes food into a <b>bolus</b>

Teeth

-mechanical (physical) digestion
-Creates greater surface area for enzymatic reactions

Salivary glands

-Chemical digestion
-<b>produces saliva</b> (~1L/day)
-Moistens food

Salivary amylase

Enzyme in saliva that breaks down starch into disaccharides

Pharynx

-where nasal and oral cavities meet
-last place where digestion is voluntarily

Epiglottis

-a flap of tissue that seals off the windpipe and prevents food from entering.

Uvula

-covers the sinuses
-pH around 7

Esophagus

-A muscular tube that connects the mouth to the stomach.
-pushes the bolus (food) towards the stomach using <b>peristalsis</b>

Peristalsis

Involuntary waves of <b>muscle contraction</b> that keep food moving along in one direction through the digestive system.

Sphincters

Control the passage of material with smooth circular muscle

Muscles arranged in circles that are able to decrease the diameter of tubes. Examples are found within the rectum, bladder, and blood vessels.

Esophageal Sphincter

a controlled opening to the <b>stomach</b> from the <b>esophagus</b>

Pyloric Sphincter

a controlled opening to the <b>small intestine</b> from the stomach

Stomach

-A muscular and elastic sac that serves mainly to store food, break it up mechanically, and begin chemical digestion of proteins and fat.
-Mechanical digestion - churns food
-Chemical digestion - releases enzymes
-Has <b>rugae</b>

Rugae

folds on inner stomach lining that increase surface area for reactions

Gastric juices

-Consists of H₂O, mucus, salt, enzymes, and hydrochloric acid.
-pH 1-3 (very acidic)! Helps kill bacteria, soften food

Enzymes & Hormones of gastric juices

Enzyme: Pepsinogen (inactive) --> Pepsin (active by HCl)
Hormone: Gastrin
Enzyme: Rennin

Pepsinogen/pepsin

-Enzyme

Pepsinogen (inactive) --> Pepsin (active) - becomes activated when in contact with HCl (hydrochloric acid). Breaks down <b>proteins</b> into <b>polypeptides</b>.

Gastrin

-Hormone

-hormone secreted in the stomach that stimulates secretion of HCl and increases gastric motility
-<b>increases acid production</b>. Stimulated by food production

Rennin

Coagulates milk protein. Can slow milk digestion so infants can get maximum nutrients

Small intestine

Digestive organ where most <b>chemical digestion</b> and absorption of food takes place

The substance produced from stomach, now called <b>chyme</b>, is pushed through via <b>peristalsis</b>.

Duodenum

First 25-30cm of the small intestine, where majority of <b>digestion takes place</b>. Enzyme secretions from the <b>pancreas</b> and <b>liver</b> travel through ducts to here.

Jejunum

Second part of the small intestine. ~2.5m, responsible for the <b>absorption of nutrients</b>.

Ileum

The third (last) and longest portion of the small intestine. ~4m. Also responsible for <b>absorption of nutrients</b>.

Duodenum completes ___________

digestion of food molecules. Enzymes include: Carbohydrases - (disaccharides) - maltase, sucrase, lactase.
<b>Enterokinase</b> - activates <b>trypsinogen</b> into <b>trypsin</b>.
<b>Peptidase</b> (erepsin) - turns peptides into smaller peptides and amino acids

Accessory organs

Organs that are not in the digestive tract, but secrete materials into tract.

Liver

makes bile salts

Bile

A substance produced by the liver that <b>breaks up fat</b> particles. (physical digestion)
Also stores excess glucose as glycogen & detoxifies blood (alcohol, medication)

Pancreas

Regulates the level of sugar in the blood

-Releases <b>bicarbonate</b> (base in duodenum) which deactivates pepsin back into pepsinogen.
-Releases enzymes into duodenum - peptidase, amylase, lipase. <b>Trypsinogen</b> (inactive) --> <b>Trypsin</b> (active). Activated by <b>enterokinases</b>. Trypsin digests partially digested proteins.

Absorption

Digested nutrients absorbed in the rest of the small intestine.

Villi

increase surface area of small intestine for more absorption

Microvilli

~130 billion per sq. inch in the small intestine

Blood capillaries

absorption through ACTIVE transport of amino acids and monosaccharides

Lacteals

absorption through PASSIVE transport of fatty acids and glycerols

Large intestine (colon)

reabsorption of water and salts (minerals). Has bacteria to produce B-12 and K vitamins.

Rectum

A short tube at the end of the large intestine where waste material is compressed into a solid form before being eliminated

Storage of feces. If full, can trigger a reflex

Anus

A muscular opening at the end of the rectum through which waste material is eliminated from the body

sphincter where waste is released from body