Chemistry of the Cell

What is the layout of a eukaryotic cell?

• Cells are made up of chemicals, DNA, RNA, Protien

• DNA is in the nucleus

What is the most important atom in biological molecules?

Carbon

What are cells made up of?

Cells are made of carbon/hydrogen based compounds (“organic” molecules) – Proteins, carbohydrates, nucleic acids, lipids

What percentage of the cell weight is water?

75-85%

Where do most cells exist?

Most cells exist in a water-containing (aqueous) extracellular environment

What is the universal solvent?

Water is the universal solvent in biological systems and is indispensable for life on Earth

What are cells made of, filled with, and surrounded by?

Cells are made of organic chemicals, filled with ion-containing water, and (usually) surrounded by water

Skin cells not surrounded by water but have water underneath

What is the most critical attribute of water?

Its polarity

What does waters polarity account for?

waters polarity accounts for:

1. Cohesiveness -water sticks to water and other things

2.Temperature-stabilizing capacity-metabolism generates heat, cells make heat, water mediates temperature

3.Solvent properties

Why is water polar?

H2O is polar due to unequal distribution of electrons – O atom is electronegative (partial negative charge) – H atoms have a partial positive charge – Water molecules are bent, not linear

What makes water molecules cohesive?

Water molecules are attracted to each other

• The electronegative oxygen of one molecule is associated with the electropositive hydrogens of nearby molecules

• These “hydrogen bonds” are about 1/10th as strong as covalent bonds

• This makes water cohesive

How does water absorb heat energy?

Heat that would raise the temperature of other liquids is first used to break hydrogen bonds in water • Water therefore changes temperature relatively slowly, protecting living systems from extreme temperature changes

Without this characteristic of water, energy released in cell metabolism would cause overheating and death

Solvent

A solvent is a fluid in which another substance, the solute, can be dissolved

Why is water a great solvent?

• Because of its polarity, water is able to dissolve a large variety of solutes

• Many of the molecules in cells are also polar and so can form hydrogen bonds or ionic bonds with water

Hydrophilic

Solutes that have an affinity for water and dissolve in it easily are called hydrophilic (“water-loving”) – Examples: most salts and sugars; some proteins, DNA, salt

Hydrophobic

Molecules that are not easily soluble in water—such as lipids—are called hydrophobic (“water-fearing”) – Examples: lipids; some proteins / parts of proteins

Why is hydrophobicity is important for biological molecules?

Determines chemical structure and interactions

Water in nature contains what?

Solutes

• Water is such a good solvent that it is rarely found in its pure form in nature – Water in nature contains dissolved ions – Chloride, sodium, potassium, calcium, magnesium, etc.

What percent salt is freshwater vs sea water?

Fresh water: <0.05% salt; seawater: ~3.5% salt

Most human cells have adapted to function in what percent salt?

0.9% salt (blood)

– Saline for intravenous injection: 0.9% NaCl

Explain water/solute interactions using NaCl

NaCl consists of Na+ cations and Cl− anions – To dissolve in a liquid, the attraction of anions and cations must be overcome • In water, anions and cations separate by taking part in electrostatic interactions with the water molecules – The polar water molecules form spheres of hydration around the ions, decreasing their chances of reassociation

small ions and cohesiveness of water make salt ions dissolve easily

What is an example of hydrophobicity?

oil

• Oil contains nonpolar (hydrophobic) lipids

Oil and water do not mix because nonpolar lipid tails are hydrophobic

What are cells surrounded by?

Membranes

Outside of the cell: extracellular • Inside of the cell: intracellular • Barrier separating these spaces: membrane – Principle component: lipid bi-layer

Membranes

• Proteins needs to be in membranes

• Membranes are made largely of Phospholipids

What does it mean by membranes being selectively permeable?

Most cell components are charged or polar, so the membrane keeps them from entering or escaping

• The internal layer is hydrophobic, large, polar, charged molecules cannot get through (Cl-, K+, Na+)

• Large uncharged molecules such as Glucose and sucrose have a very small ability to get in but not quickly or effectively

• Small uncharged polar molecules like H20 and ethanol can somewhat get in

• Small, non polar molecules like O2 and CO2 can easily get in

What are most cellular structures are made of?

Ordered arrays of linear polymers called macromolecules

Polymer

Long compound built from one or moire types of monomeric subunits

What are Important macromolecules in the cell?

proteins, nucleic acids, and polysaccharides

Protein general functions?

Various

Proteins examples?

Enzymes, hormones, antibodies, carriers, ion channels

Proteins type of monomer/ number of monomers?

Amino acids, 20

Nucleic acid general functions?

Informational

Nucleic acid examples?

DNA, RNA

Nucleic acid type of monomer/ number of monomers?

Nucleotides, 4

Polysaccharides functions

Structural, Storage

Storage Polysaccharides Example

Starch, Glycogen

Storage Polysaccharides type of monomer/ number of monomers?

Monosaccharides, one or a few

Structural Polysaccharides Examples?

Cellulose, Chitin (lobster shell)

Structural Polysaccharides type of monomer/ number of monomers?

Monosaccharides, one or a few

Lipids share some features of macromolecules but

are synthesized somewhat differently

Level 1 to 5 of the celll

LEVEL 1: Small organic molecules

LEVEL 2: Macromolecules

LEVEL 3: Supramolecular structures

LEVEL 4: Organelles

LEVEL 5: The Cell

Small organic molecules examples

Glucose Amino acids Nucleotides

Macromolecules examples

Cellulose Proteins DNA

Supramolecular structures examples

Cell wall Membrane Chromosome

Organelles examples

Chloroplast Mitochondria Nucleus

Level 5 example

A plant cell

Making polymers from building blocks

• First need a free monomer (e.g amino acid, or nucleotide) M1 is first monomer in the polymer

• Step1: Activate the monomer. The Monomer is activated by a coupling carrier C. Activation requires energy(e.g from atp)

• Step two: Condensation of activated monomers • Two active monomers undergo condensation • This produces H2O byproduct and releases one carrier (C)

• Step 3: Polymerization (elongation of the polymer) The next activated monomer (n+1) is added to a polymer that already has n monomer units

Hypertonic solution

Shriveled Cell

Isotonic solution

Normal animal cell

Hypotonic solution

Lysed animal cell

What happens if we just replace the water in cells?

Water can be replaced by intravenous delivery, but the water in our bodies contains ions (~0.9%) • Too much water will dilute these ions… hypotonic blood

Need fluids containing water and electrolytes (ions)