Biology Chapter on Lipids and Carbohydrates

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Questions and Answers

What is a major function of lipids in the human body?

Enhancement of enzymatic reactions

Formation of structural proteins

Thermal insulation against cold (correct)

Stimulation of metabolic rates

Which of the following statements about lipids is correct?

Lipids are insoluble in nonpolar solvents.

Lipids are primarily polymers of fatty acids.

Lipids can be both polar and nonpolar. (correct)

Lipids are only found in animals.

Which lipid is primarily involved in energy storage?

Cholesterol

Glycerophosphatides

Triacylglycerols (correct)

Fatty acids

Which compound does NOT belong to the group of polar lipids?

Triacylglycerols Signup and view all the answers

What role do nonpolar lipids specifically serve in the body?

Storage and transport forms of lipids Signup and view all the answers

Which lipids are known to be readily soluble in water?

Very short chain fatty acids Signup and view all the answers

What nutrient can interfere with the absorption of other nutrients if consumed in excess?

Fiber Signup and view all the answers

Which of the following does NOT classify as a lipid?

Nucleic acids Signup and view all the answers

What is a key function of carbohydrates in living organisms?

Source and storage of energy Signup and view all the answers

Which of the following statements about metabolic alkalosis is true?

It can result from excess vomiting. Signup and view all the answers

What role do glycoproteins play in Antarctic fish?

They act as anti-freeze in blood. Signup and view all the answers

Which acid-base imbalance is most commonly associated with hyperventilation?

Respiratory alkalosis Signup and view all the answers

Which of the following best defines glycomics?

Comprehensive study of glycomes Signup and view all the answers

What is a characteristic of mixed acid-base disorders?

Both HCO3- and H2CO3 are altered. Signup and view all the answers

Which of the following best describes the function of carbohydrates in cell-cell interactions?

They act as signaling molecules. Signup and view all the answers

What causes hypercapnia?

Depression of the respiratory center Signup and view all the answers

What is the primary role of glucose in the human body?

To serve as a preferred fuel for nervous tissue Signup and view all the answers

How does an adequate supply of carbohydrates affect body protein?

It spares body proteins from being used for glucose production. Signup and view all the answers

What is one of the primary physiological effects of soluble fiber?

It delays gastric emptying. Signup and view all the answers

Which type of fiber is primarily associated with promoting intestinal health?

Insoluble fiber Signup and view all the answers

Which of the following types of carbohydrates helps lower blood cholesterol levels?

Soluble fibers Signup and view all the answers

What happens when carbohydrate intake falls below 50-100 grams per day?

The body may begin to metabolize fat incompletely. Signup and view all the answers

Which type of fiber is typically found in food sources like fruits and oats?

Pectin Signup and view all the answers

How do soluble fibers benefit cardiovascular health?

By reducing blood cholesterol levels Signup and view all the answers

What are oligosaccharides classified as?

Dietary fibers Signup and view all the answers

What is the role of dietary fiber in weight control?

It contributes to satiety and delays gastric emptying. Signup and view all the answers

Study Notes

Biochemistry

Biochemistry is the study of life at the molecular level.
It uses the laws of chemistry, biology, and physics to explain processes in living cells.
Biochemistry has become the basic language of all life sciences, because life depends on biochemical reactions.

Why study biochemistry?

Biochemistry leads to a fundamental understanding of life.
It helps understand issues in medicine, health, and nutrition.
It has led to greater molecular understanding of diseases like diabetes, sickle cell anemia, and cystic fibrosis.
Future research directions in biochemistry include AIDS, cancer, and Alzheimer's Disease.
Biochemistry advances biotechnology industries. Biotechnology uses biological cells, components and properties for technologically and industrially useful operations.

Major objective of biochemistry

Complete understanding of all the chemical processes associated with living cells at the molecular level.
It isolates the numerous molecules found in cells and determines their structures.
It analyzes how these molecules function.

Further objective of biochemistry

Attempt to understand how life began.
Understanding the biochemistry of less complex life forms has direct relevance to human biochemistry.

Major chemical constituents of cells

Elements are single substances that cannot be broken down any further.
There are 110 different elements known to man.
The living matter is composed mainly of six elements: Carbon, Hydrogen, Oxygen, Nitrogen, Phosphorus, and Sulphur (CHONPS).
These elements constitute about 90% of the dry weight of the human body.
Other functionally important elements found in cells include Ca, K, Na, Cl, Mg, Fe, Cu, Co, Zn, Mo and Se.

Carbon - a unique element of life

Carbon is the most predominant and versatile element of life.
It has the unique property of forming infinite amounts of compounds due to its ability to form stable covalent bonds and C-C chains of unlimited length.
About 90% of compounds in living systems contain carbon.

Carbon can form immensely diverse compounds

Compounds are two or more elements combined and bonded together.
Carbon can form simple to complex compounds. Methane, with one carbon atom, is an example of a simple molecule. DNA, with tens of billions of carbon atoms, is an example of a complex molecule.

Organization of Life

Life is composed of lifeless chemical molecules.
This organization includes: elements, simple organic compounds (monomers), macromolecules (polymers), supramolecular structures, organelles, cells, tissues, and organisms.

Complex Biomolecules

Lipids are not biopolymers in a strict sense, though many contain fatty acids.
Major functions and building blocks of biomolecules include: Protein (amino acids), Deoxyribonucleic acid (DNA) (deoxyribonucleotides), Ribonucleic acid (RNA) (ribonucleotides), Polysaccharides (glycogen) (monosaccharides), and Lipids (fatty acids, glycerol).

Composition of the body and major classes of molecules

The human body is composed of a few elements that combine to form a great variety of biomolecules.
Biomolecules are compounds of carbon with a variety of functional groups.
Elements are the simplest kind of matter and cannot be split into two or more simpler substances by chemical reactions.

Chemical composition of a normal man (65 kg)

Constituent	Percent (%)	Weight (kg)
Water	61.6	40
Protein	17.0	11
Lipid	13.8	9
Carbohydrate	1.5	1
Minerals	6.1	4

Acid, Base and Buffer systems

Acids are H+ donors, whereas bases are H+ acceptors.
Acids and bases can be strong (dissociate completely in solution, e.g., HCl, NaOH) or weak (dissociate only partially in solution, e.g., lactic acid, carbonic acid).
A weak acid has a characteristic dissociation constant (Ka). The relationship between the pH of a solution, the Ka of an acid, and the extent of its dissociation is given by the Henderson-Hasselbalch equation.
A buffer is a mixture of an undissociated acid and its conjugate base. It resists changes in pH when H+ or OH- is added.
A buffer has its greatest buffering capacity near its pKa (the negative log of its Ka).
Two factors determine buffer effectiveness: pKa relative to the pH of the solution and its concentration.

Acid/conjugate base pairs

The general reaction is HA + H₂O ↔ A⁻ + H₃O⁺
HA represents an acid (donates an H+)
A⁻ is the conjugate base (accepts an H⁺)
The Kₐ = [H⁺][A⁻]/[HA]
pKa is a measure of the acid's strength. A large Kₐ = stronger acid; a small Kₐ = weaker acid.

Buffer systems

Buffers take up H⁺ or release H⁺ as conditions change.
Buffer pairs comprise a weak acid and a base.
They exchange strong acids or bases for weaker ones. This results in a much smaller pH change.
Principal buffers in blood are H₂CO₃/HCO₃⁻, HHb/Hb⁻, H₂PO₄⁻/HPO₄²⁻.

Bicarbonate buffer

The predominant buffer system in extracellular fluid (ECF) is the bicarbonate buffer.
It is composed of sodium bicarbonate (NaHCO₃) and carbonic acid (H₂CO₃).
The ratio of HCO₃⁻ to H₂CO₃ is maintained at 20:1.
The equation that relates pH to the components of this buffer is: pH = pKa + log[HCO₃⁻]/[H₂CO₃]

Phosphate buffer

The major intracellular buffer is the phosphate buffer. It is composed of NaH₂PO₄ and Na₂HPO₄.
The general reaction is H⁺ + HPO₄²⁻ ↔ H₂PO₄⁻

OH⁻ + H₂PO₄⁻ ↔ H₂O + HPO₄²⁻

Protein buffers

Plasma proteins and hemoglobin are protein buffers.
The carboxyl group of proteins releases H⁺, and the amino group accepts H⁺.

Respiratory mechanisms

Exhalation of CO₂ helps regulate pH. This works with volatile acids.
CO2 + H2O ↔ H2CO3 ↔ H+ + HCO3-
This does not affect fixed acids like lactic acid.
Adjustment to a changing pH occurs through the adjustment of breathing rate and depth.

Kidney excretion

The kidneys are the most effective regulator of pH.
Urine is normally acidic (~6.0).
Collected H⁺ ions are eliminated by acidified urine.
Large amounts of acid can be eliminated by the kidneys with the following processes:
Reabsorption of bicarbonate (HCO₃⁻)
Excretion of ammonium ions (NH₄⁺)
If kidneys fail, pH balance fails.

Rates of correction

Buffers function almost instantaneously.
Respiratory mechanisms take several minutes to hours.
Renal mechanisms may take several hours to days.

First and second lines of defense against pH shift

The first line of defense against pH shift is the chemical buffer system. This includes bicarbonate, phosphate, and protein buffers.
The second line of defense is the physiological buffer system. This includes the respiratory and renal mechanisms.

Acid-Base Imbalances

pH < 7.35: acidosis
pH > 7.45: alkalosis
The body responds to acid-base imbalances with compensation. The body gears up its homeostasis mechanism and makes all attempts to bring the pH back to normal.
Complete compensation brings pH back within the normal range. Partial compensation occurs when pH remains outside the normal range.

Acid-Base Imbalances (Examples)

Acidosis is a decline in blood pH.
- Metabolic acidosis- due to a decrease in bicarbonate
- Respiratory acidosis- due to an increase in carbonic acid
Alkalosis is a rise in blood pH.
- Metabolic alkalosis- due to an increase in bicarbonate
- Respiratory alkalosis- due to a decrease in carbonic acid

Compensation

If an underlying problem is metabolic, hyperventilation or hypoventilation can help with respiratory compensation.
If the problem is respiratory, renal mechanisms can bring about metabolic compensation.

Metabolic acidosis

A bicarbonate deficit (↓) – blood bicarbonate levels are below 22 mEq/L.
Causes: loss of bicarbonate through diarrhea or renal dysfunction, accumulation of acids (lactic acid or ketones), or kidneys failing to excrete H⁺.
Seen in uncontrolled diabetes (ketoacidosis).

Respiratory acidosis

Carbonic acid excess caused by blood CO₂ levels above 45 mm Hg.
Hypercapnia— high levels of CO2 in the blood.
Causes: depression of the respiratory center in the brain (e.g., drugs or head trauma), paralysis of respiratory or chest muscles, and emphysema.

Metabolic alkalosis

Bicarbonate excess — blood concentration of bicarbonate is greater than 26 mEq/L.
Causes: excessive vomiting (loss of stomach acid), excessive use of alkaline drugs, certain diuretics, endocrine disorders (e.g., aldosterone elevation), and heavy ingestion of antacids.

Respiratory alkalosis

Carbonic acid deficit — pCO₂ less than 35 mm Hg (hypocapnea).
Most common acid-base imbalance.
Primary cause is hyperventilation, e.g., hysteria, hypoxia, increased intracranial pressure, excessive artificial ventilation, or the action of drugs (e.g., salicylates) that stimulate the respiratory center.

Mixed acid-base disorders

These occur when the patient has two or more acid-base disturbances occurring simultaneously.
Both HCO₃⁻ and H₂CO₃ are altered in these cases.

Reading Assignment

Biological importance of water
Types of chemical bonds

Carbohydrates

Learning Objectives - to be able to explain what monosaccharide, disaccharide, oligosaccharide, and polysaccharide mean, describe the formation of glycosides and structures of disaccharides and polysaccharides, and explain carbohydrate roles.
Definitions - glycobiology (study of sugar functions in health and disease), glycome (all sugars in an organism), and glycomics (study of glycomes).
Sources of Carbohydrates- various food types (cereals, bread, vegetables, fruits).
Biomedical Importance (functions)- Source/storage of energy (glucose, glycogen), Structural components of cells (skin, bones, cell membranes). Involved in cell-cell interactions. Derivatives are drugs (e.g., erythromycin). Survival of Antarctic fish. Ascorbic acid is a water-soluble vitamin.
Carbohydrate functions (Metabolic/Nutritional) -- main energy component, help in bowel function, improve taste and appearance of food, used in flavors and sweeteners, regulate blood glucose. Help break down fatty acids, preventing ketosis.
Chemical Nature of Carbohydrates -- polyhydroxy alcohols with aldehyde or keto groups. Classification based on number of carbon chains (monosaccharides, disaccharides, oligosaccharides, polysaccharides).
Types of Carbohydrates -- simple carbohydrates (monosaccharides, disaccharides). Complex Carbohydrates (oligosaccharides, polysaccharides -glycogen, starches, fibers).
Monosaccharides (Glucose, Fructose, Galactose) Definitions and characteristics, Functions and structural formulas of each.
Monosaccharides - characteristics and properties -- optical isomerism, D and L designations.
Optical Activity-- Dextrorotatory and levorotatory, sign (+/-) for sugars.
Aldotetroses - structural formulas for D and L-erythrose, D and L-threose.
Aldopentoses and Aldohexoses- formulas and isomers.
Isomers and epimers - definitions and examples of each.
Functional Isomers-- definitions and examples.
Joining of monosaccharides (glycosidic bonds) – formation, enzymes glycosyltransferases.
Joining and Cleaving Sugar Molecules - condensation and hydrolysis reactions.
Disaccharides - Characteristics and functions of Maltose, Lactose, and Sucrose, structural formulas and examples.
Oligosaccharides -- characteristics and functions.
Complex Carbohydrates: Classification -- Homopolysaccharides (starch, glycogen, cellulose - structural formulas/examples); Heteropolysaccharides (e.g., glycosaminoglycans such as heparin).
Functions of carbohydrates- functions of starch, glycogen, cellulose.
Function of Glycogen- major storage polysaccharide (carbohydrate) in human body, located in liver and muscle.
Functions of Cellulose -- structural component of plant cell walls; rigid structural support.
Fiber definition, types (soluble, insoluble)- examples and functions.
Fiber- problems with too much fiber.

Lipids

Introduction - heterogeneous group of organic compounds defined by their solubility in nonpolar solvents (chloroform, ether, and benzene) and poor solubility in water; not polymers (unlike polysaccharides, proteins, and nucleic acids). Lipids are typically small molecules; may be polar or nonpolar (amphipathic). Major types are fatty acids, cholesterol, glycerophosphatides, and glycosphingolipids. Very short chain fatty acids and ketone bodies are readily soluble in water.
Occurrence -- found in humans, animals, plants, and microorganisms.
Functional uses -- thermal insulator against cold, padding against injury, energy source for cells (like carbohydrates); ideal for storing energy in the human body (higher energy content than carbohydrates and proteins, can be stored in a water-free form which is not possible with carbohydrates and proteins). Structural components of cell membranes and nervous tissue; precursors for synthesis of complex molecules (e.g., acetyl-CoA is used for the synthesis of cholesterol). Part of lipoproteins which are involved in lipid transport in blood; some lipids serve as hormones and fat-soluble vitamins. Fats essential for the absorption of fat-soluble vitamins; surfactants (reduce surface tension). Also, eicosanoids (biological actions) are derived from essential fatty acids.
Classification -- simple (fats/oils, waxes), complex (phospholipids, glycolipids, lipoproteins), derived (fatty acids, monoglycerides, diglycerides, cholesterol, ketone bodies,), and miscellaneous (carotenoids; squalene; hydrocarbons, such as pentacosane (in bees wax); terpenes).
Fatty Acids -- carboxylic acid with hydrocarbon side chain, simplest form of lipids; anionic group -- affinity for water (amphipathic nature), hydrophilic and hydrophobic regions.
Types of fatty acids -- saturated (no double bonds; solid at room temperature; contribute to cardiovascular disease [atherosclerosis]), unsaturated (one or more double bonds -- cis-isomers; liquid at room temperature), and trans fats (hydrogenated unsaturated fats; raise "bad" cholesterol; lower "good" cholesterol).
Shorthand for fatty acids -- total number of carbons, number of double bonds; position of the double bonds from the carboxyl end (Δⁿ).
Essential fatty acids (linoleic, linolenic, arachidonic acids) (cannot be synthesized, required for growth and development).
Structural uses --lipids in myelinated nerves (insulators), saturated fatty acids (microbial and anti-fungal agents), lipids (important group of parasite antigens causing filariasis, cysticercosis, leishmaniasis, schistosomiasis).
Storage lipids - fats/oils (triacylglycerols), waxes.
Steroids - complex molecules containing fused rings, steroids, sterols. Examples include cholesterol.
Compound lipids -- includes element/moieties in addition to fatty acids and alcohols. Examples: glycerophospholipids, sphingophospholipids (sphingolipids), and glycolipids (cerebrosides, gangliosides, sulfatides).
Function of glycerophospholipid -- general structure.
Function of cardiolipin -- description and function.
Function of plasmalogens.
Platelet-activating factor (PAF) -- function and description.
Function of sphingomyelin -- important component of nerve fibers and myelin sheath, provides insulation and protects the central nervous system. Description and function of sphingolipids and general structure.
Role of glycolipids -- formation of insulation for nerve system electrical activity.
Lipoproteins -- description, function as transport forms of lipids, different types (chylomicrons, VLDL, IDL, LDL, HDL), their composition, transport roles in blood plasma.

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Test your knowledge on the roles and functions of lipids and carbohydrates in the human body. This quiz covers important concepts such as energy storage, nutrient absorption, and acid-base balance. Challenge yourself with questions about glycoproteins, metabolic alkalosis, and more!