Chapter 2 - Molecules and Membranes

Cells

Complex and diverse

Water

most abundant molecule in cells

Ions and polar molecules are hydrophilic or hydrophobic

• HYDROPHILIC

• inorganic ions constitute 1% or less of the cell mass

Nonpolar molecules are hydrophilic or hydrophobic

• HYDROPHOBIC

• cannot interact with water

List the 4 organic molecules

1. Carbohydrates

2. Lipids

3. Nucleic acids

4. Proteins

Carbohydrates

simple sugars and polysaccharides

Monosaccharides

• Major nutrients of cells

• the basic formula is (CH₂O)_n

  • Glucose (C₆H₁₂O₆)

Monosaccharides are joined together by dehydration reactions called….

glycosidic bonds

Oligosaccharides

polymers of a few sugars

Polysaccharides

macromolecules; polymers of hundred or thousands of sugars

Common polysaccharides

• Glycogen, starch, cellulose, chitin

Functions of carbohydrates

• Energy

• Cell surface markers

  • they are linked to other cellular components such as lipids or proteins

  • Example - the ABO blood group

Fatty Acids

Long hydrocarbon chains with a carboxyl group (COO-)

• Unsaturated fatty acids: one or more double bonds

• Saturated fatty acids: no double bonds

How are fatty acids stored?

triacylglycerols (triglycerides or fats)

Phospholipids

principal components of cell membranes

Glycerol phospholipids

the fatty acids are bound to glycerol bound to a phosphate group

Sphingomyelin

• only non glycerol phospholipid

• polar head group is formed from serine

All phospholipids have….

hydrophobic tails and hydrophilic head groups

Many cell membranes have…

glycolipids or cholesterol

Steriod hormones

derivatives of cholesterol

Examples - estrogens and testosterone

Nucleic acids

principal informational molecules

• Deoxyribonucleic acid (DNA)

• Ribonucleic acid (RNA)

  • Messenger RNA (mRNA)

  • Ribosomal RNA

  • Transfer RNA (tRNA)

DNA vs RNA

Both - consist of purine and pyrimidine bases linked to phosphorylated sugars

DNA - two purines (adenine and guanine) and two pyrimidines (cytosine and thymine)

RNA - uracil in place of thymine

Nucleotides

one or more phosphate groups

Nucleosides

based linked to sugars

DNA vs RNA sugar

DNA - sugar 2’-deoxyribose

RNA - sugar ribose

Polymerization of nucleotides

• Phosphodiester bonds

• Oligonucleotides

• Polynucleotides

  • Always synthesized 5’ to 3’ direction

DNA - two polynucleotide chains

• bases are on the inside, joined by H-bonds

• complementary base pairs (guanine with cytosine — adenine with thymine)

Proteins and Functions

• Most diverse

• several thousand different proteins

• direct almost all activities

Functions

• Structure

• Transport and storage

• Transmission

• Defense

• Enzyme

How many different amino acids are there

20 different AA

How are amino acids grouped?

By their side chains

• nonpolar

• polar

• charged basic groups

• acidic

How are amino acids joined and what are they called?

• Peptide bonds join AA

• Called polypeptides

X-Ray crystallography

laboratory method used to fine the 3D arrangement of atoms inside a crystal

What are the proteins structure levels?

• Primary

• Secondary (alpha and beta sheet)

• Tertiary

• Quaternary

Cell membranes - Phospholipids

• associated with proteins

• aggregate in water

• from phospholipid bilayer

Cell membranes are localized in different places

• Plasma membrane

• Subcellular organelles

  • Nucleus

  • mitochondria

  • many other organelles

True or False: Membranes do not have selective permeability.

False, they have do have have selective permeability

• Small, nonpolar molecules can diffuse across

• Ions and larger uncharged molecules cannot diffuse across

True or False: Molecules freely rotate and move.

True

Unsaturated fatty acids chains = double bonds create kinks

Cholesterol

• membrane fluidity

• rigidity

• maintains membrane fluidity

Fluid Mosaic Model

• Intergral membrane proteins - directly

• Peripheral membrane proteins - indirectly

• Transmembrane proteins - expose to both sides

β-barrel proteins

present in some bacteria, chloroplasts, and mitochondria

Channel proteins

open pores across membrane

• ion channels - pass inorganic ions

Carrier proteins

selective and transports small molecules

Passive transport

concentration and electrochemical gradient

Active transport

require energy to transport against concentration gradient