Unit 2: Cell Membrane Structure Vocabulary

Carbon Bonding

Carbon can form up to 4 (single or double) covalent bonds

Covalent bonds

Created by sharing electrons (strongest bond)

Six most common elements in life

Carbon, hydrogen, nitrogen, oxygen, phosphorous, sulfur (CHNOPS)

Tetrahedron

Shape that carbon takes on after making four single bonds

Metabolism

Sum of all chemical reactions that occur within an organism

Functions of metabolism (2)

Energy for cellular processes; synthesis and assimilation of new materials

Anabolism

Joining of simple molecules (monomers) to produce complex ones (polymers); condensation reaction; endergonic

Condensation

Removal of H20 to link bonds; water formed from OH (hydroxyl) from one monomer and H from another

Endergonic

Requires energy

Catabolism (digestion)

Breaking of complex molecules (polymers) to produce simple ones (monomers); hydrolysis; exergonic

Hydrolysis

Splitting of molecules by adding water

Exergonic

Releases energy

Carbohydrates

Monomer: Monosaccharide;

Polymer: Polysaccharide

Bond: Glycosidic

Glycosidic Bond

Covalent bond between two monosaccharides (C-O-C)

Carbohydrate Function

Short-term energy storage, structure

Glucose Characteristics

Soluble, chemically stable, yields energy when oxidized (lose electron)

Starch

Plant energy storage made of alpha glucose (amylose or amylopectin)

Amylose

Unbranched, helical (1-4 bonds), compact, more difficult to digest; type of starch

Amylopectin

Branched, 1-4 and 1-6 Bonds (1-6 bonds cause branching), easier to digest due to greater surface area; type of starch

Glycogen

Animal energy storage made of alpha glucose; unbranched (1-4) and branched (1-6); stored in liver in animals

Polysaccharide Characteristics

Large in size, but relatively compact due to coiling and branching; low solubility

Cellulose

Plant structure (cell wall) made of beta glucose; unbranched (1-4 bonds); indigestible for most (lack enzyme)

Alpha vs. Beta Glucose

structural isomers; position of hydroxyl on C1 is different

Beta-Glucose Bonding

Alternating OH groups allow additional hydrogen bonding; forms cross-link to provide tensile strength

Images of Glucose Polymers

Glycoproteins

Polypeptides with oligosaccharides, found in plasma membranes; used for cell recognition & tissue formation

Oligosaccharides

Short chain of sugar (3-10)

ABO Glycoproteins

Red blood cells have glycoproteins that are used for identification purposes and affect transfusion

Lipids

Include fats, oils, waxes, and steroids;

Hydrophobic (or lipophilic), more attracted to nonpolar (not necessarily repelled by H2O)

DOES NOT CONSIST OF MONOMERS AND POLYMERS

Lipid Function

Long-term energy storage

Triglycerides

One glycerol + three fatty acids form via ester bonds

Ester Bonds

Hydroxyl on glycerol loses H, carboxyl on fatty acid loses OH to form H2O; O-C=O

Phospholipids

Phosphate + two fatty acids; amphipathic

Lipophilic

Fat-loving, similar to hydrophobic

Fatty Acids Characteristics

Long hydrocarbons;

CH3 (methyl) at one end and COOH (carboxyl) on the other

Saturated Fatty Acids

No double bonds, "saturated" with hydrogens;

Linear, come from animal sources;

High melting point - solid at room temperature

Unsaturated Fatty Acids

Has double bonds, bent;

Come from plant sources;

Low melting point - liquid at room temp (typically)

Monounsaturated/Polyunsaturated Fatty Acids

Mono = 1 double bond;

Poly = more than 1 double bond

Cis Unsaturated Fatty Acids

Two H atoms adjacent to double bond are on same side, hydrogens repel one another, forming kinks

Trans Unsaturated Fatty Acid

Two H atoms adjacent to double bond are on opposite sides, produced in industrial process called hydrogenation (now banned);

Makes fats "spreadable" such as margarine;

Linear and solid at room temp, despite double bonds

Cis vs Trans Unsaturated Fatty Acids

Lipid Advantages over Carbohydrates (5)

Chemically stable, energy not lost over time;

Immiscible in H2O, no effect on osmotic pressure of cell;

Store 2x energy;

Poor heat conductors, used as thermal insulators such as blubber;

Act as shock absorbers

Proteins

Monomer: amino acid

Polymer: polypeptide

Bond: peptide

Amino Acid Structure (5)

alpha carbon;

NH2 (amino group), beginning;

COOH (carboxyl group), add to this end;

lone hydrogen;

R group (variable)

Amphiprotic

Molecule that has parts that can donate hydrogen and parts that can receive them (ex. amino acid)

R-Groups

Residue Group; define chemical characteristics of AAs by determining folds/bonding

Synthesis of Polypeptides

Formed by condensation;

Forms peptide bond (C-N) and H2O;

*COOH always loses the OH, NH2 loses H*

Catalyzed by Ribosomes;

Polypeptide Directionality

N-terminus: NH2 end;

C-terminus: COOH end

Results in repeated sequence of N-C-C-N-C-C in backbone

Dipeptide Image

Essential AAs

Cannot be made in sufficient amounts by ORG, must be obtained through food

Non-Essential AAs

Can be made by the body via metabolic pathways

Proteome

Total amount of proteins that can be synthesized in the organism (> genome) due to splicing and modification

Primary Structure

Linear sequence of AAs, determined by DNA, formed via only peptide bonds btwn amino acids (covalent)

Secondary Structure

Exists as alpha helices & beta pleated sheets;

hydrogen bonds btwn carboxyl & amines groups of nearby AAs (not interaction btwn R-groups)

Alpha Helices

Spiral arrangement w/ h-bonds btwn adjacent turns

Beta-pleated sheets

Parallel strand arrangement w/ H-bonds btwn them

Tertiary Structure

Polypeptides 3D conformation, determined by R-groups

Bonds found in Tertiary Structure

Covalent:

-strongest, disulfide bridge (S-S); occurs btwn cysteins

Ionic:

-bonds formed btwn positively/negatively charged R-groups

Hydrogen Bonds

Hydrophobic Interaction

Chaperone Proteins

Proteins that help other proteins fold correctly

Quaternary Structure

Consists of more than 1 polypeptide chain, doesn't always happen

Types: non-conjugated and conjugated

Non-conjugated proteins

Only polypeptide chains; chains are bonded using all bonds found in tertiary structure interactions

Conjugated proteins

Contains one or more non-polypeptide subunits (prosthetic)

Ex. Hemoglobin, 4 polypeptides, each w/ prosthetic group

Prosthetic Group

Non-protein component of a conjugated protein (ex. heme group of hemoglobin)

Protein Form and Function

Structure = Function

DNA sequence, leads to specific AA sequence, leads to Unique r-group interaction, leads to 3D shape, leads to Function

Fibrous Proteins

Elongated polypeptides that lack folding found in secondary & tertiary structures (ex. collagen

Globular Proteins

Rounded by shape created via foldings, stabilized via r-group interactions (ex. insulin)

Cell Membrane

Bilayer of phospholipids that form a continuous barrier

Cell Membrane Function

Separates cell from environment & controls passage of particles

Phospholipid bilayer

Hydrophobic tails attracted to each other, hydrophilic heads H-bond with cytosolic (inside cell) and extracellular (outside cell) fluids

In aqueous environment, phospholipids spontaneously arrange into _________ (sphere)

Fluid-Mosaic Model

Fluid - phospholipids move freely laterally;

Mosaic - has embedded different types of proteins (like tiles in a mosaic)

Fatty Acids in Cell Membrane

Sustained by hydrophobic interaction, drifts laterally but not transversely

Saturated fatty acids in membrane

Straight, packs tightly, increases density of membrane, decreases fluidity and permeability

Unsaturated fatty acids in membrane

Kinks, bent, packs loosely, decreases density, increases fluidity and permeability

*Ratio of saturated and unsaturated fatty acids are regulated, must be fluid but intact, must be permeable but not perforated*

Steroid

4 fused carbon rings, 3 cyclohexane rings, 1 cyclopentane ring

Cholesterol

Maintains membrane fluidity and stability in animal cells; located between saturated fatty acids to create gaps between phospholipids

Cholesterol Function

Controls membrane fluidity;

Buffers against temperature changes

in high temp - maintains impermeability

in low temp - stops crystallization;

Secures peripheral proteins

Glycoproteins and Glycolipids

Involved in Cell to cell recognition

Glycolipids

Lipid embedded in hydrophobic core w/ carbs projecting out (ex. antigen)

Glycocalyx

Used for cell adhesion & recognition;

formed w/ glycoproteins and glycolipids - carbohydrate-rich layer outside of membrane

Cell-adhesion Molecules (CAMs)

When same types of CAMs bind, leads to tissue; different types of CAMs or to extracellular matrix, leads to junction (usually more complex structure)

Semi-Permeable

Determined by size & polarity;

small or nonpolar will cross, large or polar will not;

different from selective, won't choose specific things to let cross like Cl- channels

Passive Transport

Particles are in continuous, random motion ******

move down their own [ ] gradient from high to low; no ATP; move towards equilibrium, once reached, no NET movement (but molecules keep moving)

Types of Passive Transport

simple diffusion, osmosis, facilitated diffusion (w/ channels)

Simple Diffusion

Particles move directly through membrane (if permeable; from high to low [ ]; until equilibrium is reached

Factors that affect Diffusion

temperature, size of particle, steepness of gradient

Solvation

Combination of solvent and solute

Reason for Osmosis

Solutes in H2O can move, but cannot separate from H2O, therefore they restrict H2O movement.

Some solutes cannot cross the cell membrane, resulting in movement of water, rather than solutes

Osmosis

Passive movement of H2O across membrane from low solute [ ] to high solute [ ] until dynamic equilibrium is reached

Solutions w/ greater concentrations have more osmotically active solutes, therefore more intermolecular interactions w/ H2O

Dynamic Equilibrium

State where there is continuous movement of particles but no overall (net) change in concentration

Concentration (Osmolarity)

solute per volume of solution (mol DM^-3) or (mol/L)

Hypertonic

high concentration of solute, therefore water moves towards it; both cell or solution can be hypertonic

Hypotonic

low concentration of solute, therefore water moves away from it; both cell or solution can be hypotonic

Isotonic

Same solute concentration, therefore no net water movement - at dynamic equilibrium

Tonicity

Ability of solution to cause a cell to gain/lose water

Tonicity of Animal Cells

isotonic - *optimal;

hypertonic - cell shrivels (crenation)

hypotonic - cell lysis

Crenation

When a cell shrinks and shrivels;

originated from describing RBCs

Contractile Vacuoles

Used in freshwater unicellular organisms to remove incoming water, typically needed when in hypotonic solution (ex. freshwater paramecium)

Tonicity of Plant Cells

isotonic - cells are flaccid, plants wilt;

hypertonic - cells plamolyze, platns die;

hypotonic - cells are turgid, *optimal

Turgor Pressure

pressure that water exert against cell wall

Plasmolysis

cytoplasm shrivels and plasma membrane detaches from cell wall; occurs in hypertonic environment