Chapter 3: Part II Biochemistry

• Water makes up between 60 and 70% of organisms’ bodies

• Polarity

• Molecules with partial charges on opposite ends are polar

• Oxygen atoms are larger than hydrogen,

so electrons spend more time near oxygen, giving it a slight negative charge, and hydrogen a slight positive charge.

Why is polarity important?•“Like dissolves like” – polar substances are good at dissolving other polar substances and substances that are ionic – hydrophilic•Ex: sugar and salt

•Polar substances DO NOT dissolve substances that are nonpolar (without charged ends) – hydrophobic•Ex: oil, grease, wax

•Polarity helps chemical reactions to take place.

Negative ends of water are attracted to Na+

Positive ends of water are attracted to Cl-

• Hydrogen bonds form when a covalently-bonded H+ is attracted to a negatively-charged atom in a neighboring molecule (such as oxygen in neighboring water molecule, or chlorine in NaCl).

• Hydrogen bonds are relatively weak bonds.

Properties of water•Ice floats•Water absorbs and retains heat•Water molecules stick to each other•Water molecules stick to other polar substances

•Ice floats:•When water freezes, hydrogen bonds lock water molecules into a structure that has empty spaces, making it less dense than liquid water

Liquid water Ice

Water absorbs and retains heat•Because of hydrogen bonds, water can absorb large amounts of energy•Absorbs lot of heat before it boils

•Helps keep cells at an even temperature despite changes in the environment – homeostasis again!!•Allows large bodies of water to maintain a relatively constant temperature.

Water molecules stick to each other•Cohesion – the attraction of water molecules to each other

•Cohesive forces are strong enough to cause water to act as though it has a thin “skin” on its surface – surface tension.

Jesus lizards walking on surface tension

Water molecules stick to other polar substances

•Adhesion - the attraction between particles of different substances.•Ex: Water sticks to the surface of your car after it rains, sticks to your skin after a shower

•Capillarity - adhesion and cohesion enable water molecules to move upward through narrow tubes •Ex: water moving through a stem of a plant, helps blood flow in blood vessels

Organic Molecules

• Examples: carbohydrates, lipids, proteins, nucleic acids

• Always contain carbon • Why carbon? Carbon has 4 electrons in

outer shell – can form covalent bonds with up to 4 other atoms.

•Carbon can share electrons with other carbon atoms to form a chain

•Hydrocarbon chain can turn back on itself to form a ring

CarbohydratesImportance:• Quick energy and short-term energy

storage• Make up cell wall in plants• Make up shells of crabs, lobsters and

insects• Help cells to recognize one another

•Monosaccharides (single sugar): •glucose – blood sugar•fructose – found in fruit•galactose – found in milk

•Glucose, fructose, and galactose all have the same molecular formula, C6H12O6, but different structural formulas

Fructose Galactose

Glucose

•Below are 3 ways to represent glucose:

• Disaccharide - made from linking two monosaccharides together.

• Examples of disaccharides:• Maltose = glucose + glucose• Sucrose = glucose + fructose• Lactose = glucose + galactose

Sucrose

•Polysaccharides – contain many glucose units

•Ex: starch, glycogen, & cellulose

•Starch -can be up to 4000 glucose units

•Ex: Glycogen – after eating starchy foods, the body converts glucose in the blood into glycogen – stored in liver and released as needed

•Ex: Cellulose – found in plant cell walls. •Glucose units joined in such a way that we can’t digest it – passes through as roughage – may help prevent colon cancer

•Foods they can be found in:•Simple sugars –Fruit, milk, sweets, sodas, juices

•Starches – Breads, pasta, rice, corn, wheat, cereal, leafy vegetables, carrots

Lipids

• Examples:

• Fats - solid at room temp. – animal origin

• Oils - liquid at room temp. – plant origin

• Waxes – protective covering on plants & animals

• Phospholipids and steroids

• Lipids do not dissolve in water - nonpolar

Importance:

•Long-term energy reserves

•Form membranes in cells

•Hormones such as testosterone and estrogen

•Insulation, nerve impulses

•Repel water – duck feathers

•Structure – 1 glycerol plus 3 fatty acid molecules

• Saturated vs. unsaturated fatty acids:

• Saturated – no double covalent bonds between carbon atoms – makes butter and lard solids

• Monounsaturated – has 1 double bond between carbon atoms

• Polyunsaturated – 2 or more double bonds – makes cooking oil liquid

• Unsaturated and polyunsaturated are better for you than saturated fats

•Foods they can be found in:•Butter, foods fried in oil, bacon, red meat, cheese

Proteins

Importance:

• Build living tissue – hair, nails, tendons, ligaments, muscle, bone, etc.

• Act as enzymes to speed reactions

• Act as antibodies to fight disease

Proteins are made of amino acids• Central carbon atom

• Hydrogen atom

• Amino group (-NH2)

• Carboxyl group (-COOH)

• “R” group – which differs between amino acids

Amino acids are joined by peptide bonds to form polypeptides.

•Foods they can be found in:•Meat, eggs, cheese, beans, nuts, soy

Levels of organization:

• Shape of protein is related to its function.• When exposed to extremes in heat or pH,

proteins change their shape – undergo denaturation – normal bonding between R groups is disturbed.

• Change cannot be reversed – protein no longer works.

Nucleic Acids

• Examples: DNA (deoxyribonucleic acid) and RNA (ribonucleic acid)

• Importance: molecules of inheritance – needed for cell reproduction and making proteins

•Structure – made of nucleotides.

DNA is double-stranded, with complementary base pairing – A and T, C and G always pair.