Molecules of Life

Molecules of Life

Molecules of life are synthesized by living cells• Carbohydrates• Lipids • Proteins • Nucleic acids

Organic Compounds

Consist primarily of carbon and hydrogen atoms• Carbon atoms bond covalently with up to four

other atoms, often in long chains or rings

Functional groups attach to a carbon backbone • Influence organic compound’s properties

An Organic Compound: Glucose

Four models

Functional Groups: The Importance of Position

Processes of Metabolism

Cells use energy to grow and maintain themselves

Enzyme-driven reactions build, rearrange, and split organic molecules

Building Organic Compounds

Cells form complex organic molecules• Simple sugars → carbohydrates• Fatty acids → lipids• Amino acids → proteins• Nucleotides → nucleic acids

Dehydration synthesis combines monomers to form polymers

Dehydration synthesis and Hydrolysis

Carbohydrates – The Most Abundant Ones

Three main types of carbohydrates• Monosaccharides (simple sugars)• Oligosaccharides (short chains)• Polysaccharides (complex carbohydrates)

Carbohydrate functions• Instant energy sources • Transportable or storable forms of energy• Structural materials

Oligosaccharides: Sucrose

Complex Carbohydrates: Starch, Cellulose, and Glycogen

c Glycogen. In animals, thispolysaccharide is a storage form for excess glucose. It is especially abundant in the liver and muscles of highly active animals, including fishes and people.

Structure of cellulose

Greasy, Oily – Must Be Lipids

Lipids • Fats, phospholipids, waxes, and sterols• Don’t dissolve in water• Dissolve in nonpolar substances (other lipids)

Lipid functions• Major sources of energy• Structural materials• Used in cell membranes

Fats

Lipids with one, two, or three fatty acid tails• Saturated

Triglycerides (neutral fats )• Three fatty acid tails• Most abundant animal fat (body fat)• Major energy reserves

Triglyceride Formation

Phospholipids

Main component of cell membranes • Hydrophilic head,

hydrophobic tails

Waxes

Firm, pliable, water repelling, lubricating

Steroids: Cholesterol

Membrane components; precursors of other molecules (steroid hormones)

Protein Structure

Built from 20 kinds of amino acids

Four Levels of Protein Structure

1. Primary structure • Amino acids joined by peptide bonds form a

linear polypeptide chain

2. Secondary structure• Polypeptide chains form sheets and coils

3. Tertiary structure• Sheets and coils pack into functional domains

Four Levels of Protein Structure

4. Quaternary structure• Many proteins (e.g. enzymes) consist of two or

more chains

Levels of Protein Structure

Levels of Protein Structure

Levels of Protein Structure

Levels of Protein Structure

Why is Protein StructureSo Important?

Protein structure dictates function

Sometimes a mutation in DNA results in an amino acid substitution that alters a protein’s structure and compromises its function• Example: Hemoglobin and sickle-cell anemia

Normal Hemoglobin Structure

VALINE HISTIDINE LEUCINE GLUTAMATEVALINETHREONINE PROLINE

sickle cell

normal cell

b One amino acid substitution results in theabnormal beta chain in HbS molecules. Insteadof glutamate, valine was added at the sixthposition of the polypeptide chain.

c Glutamate has an overall negative charge; valine has no net charge. At low oxygen levels, this difference gives rise to a water-repellent, sticky patch on HbS molecules. They stick togetherbecause of that patch, forming rod shaped clumps that distort normally rounded red blood cells into sickle shapes. (A sickle is a farm tool that has a crescent-shaped blade.)

Clumping of cells in bloodstream

Circulatory problems, damage to brain, lungs, heart, skeletal muscles, gut, and kidneys

Heart failure, paralysis, pneumonia, rheumatism, gut pain, kidney failure

Spleen concentrates sickle cells

Spleen enlargement

Immune system compromised

Rapid destruction of sickle cells

Anemia, causing weakness,fatigue, impaired development,heart chamber dilation

Impaired brain function, heart failure

d Melba Moore, celebrity spokes-person for sickle-cell anemia organizations. Right, range of symptoms for a person with two mutated genes for hemoglobin’s beta chain.

Denatured Proteins

If a protein unfolds and loses its three-dimensional shape (denatures), it also loses its function

Caused by shifts in pH or temperature, or exposure to detergent or salts • Disrupts hydrogen bonds and other molecular

interactions responsible for protein’s shape

Nucleotides, DNA, and RNAs

Nucleotide structure, 3 parts:• Sugar• Phosphate group• Nitrogen-containing base

Nucleotide Functions: Reproduction, Metabolism, and Survival

DNA and RNAs are nucleic acids, each composed of four kinds of nucleotide subunits

ATP energizes many kinds of molecules by phosphate-group transfers

Nucleotides of DNA

DNA, RNAs, and Protein Synthesis

DNA (double-stranded)• Encodes information about the primary structure

of all cell proteins in its nucleotide sequence

RNA molecules (usually single stranded)• Different kinds interact with DNA and one another

during protein synthesis

covalentbonding incarbonbackbone

hydrogen bondingbetween bases