Biology 20 - Chapter I

Digestion and Human Health

Nutrition

the process of taking and assimilating nutrients; the branch of science concerned with this process

Nutrients

a substance that provides nourishment essential for life and growth

Macromolecules

large, complex organic molecules. Made up of smaller subunits linked together by covalent bonds.

Organic molecules that make up living organisms

Carbohydrates, Proteins, Lipids, Nucleic Acids, and VItamins and Nutrients

Assembling Macromolecules

Dehydration Synthesis - a molecule of water is removed by taking the -OH (hydroxyl) group of one subunit and a -H (hydrogen) atom from another subunit. This leaves the subunits bonded together.

DIsassembling Macromolecules

Hydrolysis - a molecule of water is added to the bonds between subunits breaking them apart.

Carbohydrates

The most important energy source for the body; produced by plants during photosynthesis.

Provide short or long term energy storage and are classified by the amount of sugars they contain.

Three types: monosaccharides, disaccharides, and polysaccharides

Simple sugars

1 carbon, 2 hydrogen, 1 oxygen.

Often end in “-ose”

Monosaccharides

Contain 3-6 carbons

Examples: Glucose, galactose, fructose

Disaccharides

Two monosaccharides

Formed by dehydration synthesis

Examples:

Sucrose = glucose + fructose

Maltose = glucose + glucose

Lactose = glucose + galactose

Polysaccharides

More than 2 monosaccharides

Formed by dehydration synthesis

Starch

Polysaccharide that acts as energy storage in plants, made up of 100 - 1000 glucose units

Glycogen

Stored by animals as a carbohydrate, made up of 16 - 24 glucose units joined by dehydration synthesis

What happens to excess glucose?

Converted into glycogen by insulin and is stored in liver and muscles.

What happens if glucose concentration in blood decreases?

Glycogen can be converted back into glucose

Cellulose

Polysaccharide that makes up the cell wall of plant cells.

Made up of thousands of glucose units combined by dehydration synthesis in long chains.

The most abundant carbohydrate in nature.

Can’t be digested and used for food by humans but is an important source of fibre in our diet.

Benedict’s Test

Blue reagent turns red/orange when exposed to heat if sugars are present.

Test for Carbohydrates

Iodine Test

Iodine (yellowish/red/brown) turns blue/black in the presence of starch.

Test for Carbohydrates

Lipids

Composed of carbon, hydrogen, and oxygen.

Large, insoluble molecules which are ideal for their primary role in the body.

Major component of cell membrane and many hormones.

Body’s insulation from cold.

Cushioning agent for many organs.

Carrier of vitamins A, D, E, and K.

Composed of glycerol and fatty and chain

Triglycerides

Lipid composed of glycerol and 3 fatty acids.

Dehydration synthesis!

Three water molecules are formed in this process

Unsaturated triglycerides

double bonds, more easily broken down (oils), from plant sources

Saturated triglycerides

no double bonds, not easily broken down (fats), from animal sources, solids at room temperature, fats accumulate on arteries

Phospholipids

Lipid composed of a phosphate group attached to glycerol.

Major component of cell membranes.

Twice the energy as carbohydrates or proteins.

Waxes

Composed of many fatty acids attached to alcohols or carbon rings.

Insoluble in water

Not readily used as energy food but as a waterproofing covering of leaves, feathers, and fur.

Also used in the structuring of storage units in beehives

Translucence test

Greasy, translucent spot produced on paper.

Test for Lipids

Emulsions test

Milky emulsion (tiny droplets) produced by alcohol dissolved fat added to water.

Test for Lipids

Sudan IV

Red droplets of fat produced.

Test for Lipids

Steroids

Altered lipids that are produced by the body and act as chemical messengers known as hormones.

Can have many unwanted effects

Cholesterol

Type of steroid

Found in the body and made in the liver

An important component of cell membranes and used to manufacture certain hormones

LDL Cholesterol (Low Density Lipoprotein)

Bad cholesterol

The build up of cholesterol and fats forming plaque along the inside lining of the arteries

Can cause high blood pressure or a stroke, if the blockage is in the brain or a heart attack, if the plaque blocks thee coronary artery.

HDL Cholesterol (High Density Lipoprotein)

Good cholesterol

Can cover the blood’s bad cholesterol

Exercise can raise it

Protein

Composed by carbon, hydrogen, oxygen, and nitrogen. sometimes contain sulfur.

Built by combining amino acids using dehydration synthesis

amino acids → polypeptides →proteins

Polypeptide

Chain of 3 or more amino acids

Protein

Longer amino acid chains consisting of one or more polypeptide changes folded into complex 3D structures

Peptide bond

Formed when amino acids are joined

Place where the protein and later be broken down by hydrolysis and digestion

What happens when there is too much protein?

Kidney failure (clogs kidney with wastes)

What happens when there is too little protein?

Kwashiorkor (bellies swell because of water retention)

What do proteins do?

building and repairing cell structures

muscle fibres

enzymes

antibodies

some hormones

markers and receptors

active transport molecules

Primary Structure

Amino Acids are organized in linear arrangements.

Determined by DNA in the nucleus of the cell

Secondary Structure

Primary structure coils or pleated sheets

Tertiary Structure

Spiral chains folded upon themselves to give a globular appearance.

Quaternary Structure

Several globular proteins bonded together

Denaturation

Occurs when the bonds holding the protein molecule together are disrupted. Causes a temporary change in the protein’s shape and properties

Coagulation

Permanent change in protein shape

Biuret test

blue reagent turns violet when peptide bonds (proteins) are present

Nucleic Acids

Found in hereditary materials of a cell

Two main types: DNA and RNA

Made up of Nucleotides joined by dehydration synthesis

Nucleotides

Made up of a five carbon sugar (ribose or deoxyribose), a phosphate, and a nitrogen base

Vitamins

Group of organic substances that help in enzyme actions

Made up by plants

Animals need them but can’t make them; thus they need to be taken in as food.

Vitamin A

beauty vitamin (skin/hair/nails) and visual pigment (at night)

Vitamin B

energy metabolism

Vitamin C

bones/teeth, immune system, connective tissue

Vitamin D

calcium absorption (bones/teeth)

Minerals

Group of inorganic substances that have various functions:

Maintain electrolyte balance in body fluids

Act in the nerve and muscle cells

Form structures such as teeth and bones

Help in enzyme actions in other macromolecules

Example: calcium, iron, iodine, potassium/sodium

Calcium

Growth of bones/teeth (rickets)

Iron

Blood hemoglobin (anemia)

Iodine

Part of a hormone called thyroxin (goiter)

Potassium/Sodium

Nerve impulse (nerve disorders)

Enzymes

Functional 3-D proteins that act as biological catalyst

Often end with -ase and are named for their substrates

Activation energy

Needed to start a chemical reaction, usually heat.

Problem: for cells to start reactions they need to put in energy; but temperature increase can coagulate their proteins and the cells die

Solution: enzymes lower the necessary energy of activation

Substrate

Molecule to which the enzyme attaches itself

Active site

Area of an enzyme that attaches wit the substrate molecule

Enzyme helpers

cofactors and co-enzymes

Cofactors

inorganic molecules, atoms, or ions that can help enzymes bind to substrate molecules

made up from minerals

Co-enzymes

organic molecules that help enzymes bind to substrate molecules

made up from vitamins

Factors affecting enzyme activity

Temperature, pH, Concentration of Substrate, Concentration of Enzyme, Inhibitors

Temperature

More = faster reaction

Having a higher _____ can denature the enzyme stopping it from working - active site an no longer bind substrate molecules

Enzymes work at an optimum _____

pH

Enzymes work at its optimum _____

Change in acidity or basicity an alter enzyme shape

Active site can no longer bind substrate molecules

Concentration of Substrate

Enzymes work slowly with low _____

Usually more substrate increases reaction rate

When the enzyme is working as fast as it can, more substrate will not make it work faster, the enzyme has reached maximum velocity.

Concentration of Enzyme

Increases the reaction rate, providing there is an unlimited supply of substrate

Inhibitors

Competitive and Non-Competitive

Competitive Inhibitors

Compete with the substrate for the active site on the enzyme. If they bond to the enzyme they stop the reaction.

Loosely bound to the active site though and can be replaced by the substrate, therefore the effect is irreversible.

Its degree depends on the relative concentrations of it and the substrate

Non-Competitive Inhibitors

Attaches to the enzyme changing the shape of the active site = the substrate cannot bind.

This is an irreversible event. Adding more substrate will not reactivate the enzyme

Regulation of Enzyme Activity

(Negative Feedback/Feedback Inhibition)

Enzymes participate in a metabolic pathway where the substrate is modified by a number of enzymes before producing a final product.

As the final product accumulates within the cell, it binds to the regulatory site of an enzyme in the pathway, changing its shape, and thus preventing the substrate from binding.

The final product is no longer produced until concentrations are reduced.

Precursor

Accumulation of substrate molecules causes these molecules to attach to the regulatory site of one of the enzymes in a pathway, which improves fit between enzyme and substrate - increases reaction rate

Digestion

Breaking down of food into materials needed by the body:

polymers → monomers → absorbed into mitochondria → ATP

Materials needed by the cells

Monosaccharides

Amino Acids

Fatty Acids and Glycerol

The Process of Digestion

Ingestion, Digestion, Absorption, Assimilation, and Elimination

Ingestion

The intake of the nutrients

Digestion

Breaking down of large organic compounds into smaller ones

Absorption

Transferring the small useful compounds from the digestive system into the circulatory system

Happens in the stomach, the small intestine, and the large intestine

Assimilation

Use of nutrients by the cells of the body

Elimination (egestion)

Passing left over wastes out of the digestive tract

Physical or Mechanical Digestion

Physically breaking down ingested food

Chewing (mouth) and churning and mixing (stomach)

Chemical Digestion

Breaking down ingested food by enzymes and other digestive secretions

Alimentary Canal

A continuous, coiled, and hollow muscular tube that food passes through

Accessory Organs

Makes chemicals needed for digestion and send them into the alimentary canal: Salivary glands, liver, gallbladder, pancreas

The Mouth

Site of ingestion of food

Chemical and Physical Digestions

Saliva

Contains salivary amylase enzyme

Breaks down starch ( a polysaccharide ) → maltose (disaccharide)

Allows for the formation of a bolus (ball of food) for ease of swallowing

Secreted by the salivary gland

Composed by water, mucus, salt, and salivary amylase

Water

Lubricates food, makes it easier to swallow

Dissolves food, so it can be tasted

Moistens lips and tongue for speech

Cleans mouth of debris

Mucus

Lubricates food and protects wall of the stomach

Salts

Provides basic pH, approx 7.6, for action of amylase

Salivary amylase

Digestion of starch → maltose

Pharynx

Swallowing moves materials to the throat

Intersection that leads to the trachea (respiratory) and the esophagus (digestive).

The epiglottis prevents food from entering the trachea

Esophagus

Muscular tube that moves food from the mouth to the stomach

Not a digestive organ

Peristalsis

Waves of muscular contraction moves food down the esophagus to the stomach

Stomach

Site of both chemical and mechanical digestion

Can hold food for 30 minutes to several hours depending on the type of food

Physical Digestion of the Stomach

Churning (breaks up food)

Chemical Digestion of the Stomach

proteins → polypeptides-milk proteins → coagulation

What is absorbed by the stomach?

Water

Salts

Aspirin

Alcohol

Sphincter muscles

It seals the stomach by both ends

Regulates the flow of food

Two types:

esophageal (esophagus to stomach)

pyloric (stomach to duodenum)