SA#3 Bio Reviewer Cycle 6-7

Prominence of Membranes

An essential feature of every cell is the presence of membranes that defines the boundary of the cells and any internal compartments

Functions of Membranes

Membranes not only define the cell and its organelles but important functions, including transports, signaling, and adhesion.

The Plasma Membrane

- In all cells, the plasma membrane consists of a phospholipid bilayer with numerous proteins embedded in it.
- Cholesterol provides support

Phospholipids

- Amphipathic because it is composed of
- Hydrophilic regions - polar
- Hydrophobic regions - non-polar
- Lipids are small nonpolar molecules (e.g O2 and CO2) pass freely across

Saturated Fat

At room temperature, the molecules of a saturated fat, such as the fat in butter, are packed closely together, forming a solid.

Structural formula of a saturated fat molecule (Each hydrocarbon chain is represented as a zigzag line, where each bend represents a carbon atom; are not hydrogens shown.)

Space-filling model of stearic acid, a saturated fatty acid (red oxygen, = black carbon, gray = hydrogen)

Unsaturated Fat

At room temperature, the molecules of an unsaturated fat such as olive oil cannot pack together closely enough to solidify because of the kinks in some of their fatty acid hydrocarbon chains.

Structural formula of an unsaturated fat molecule

Space-filling model of oleic acid, an unsaturated fatty acid

Due to the presence of double bonds in the hydrophobic tail of phospholipids, a kink (bend) is formed. This causes the membrane to be “fluid”

Fluid Mosaic Model

The membrane is a mosaic of protein molecules bobbing in a fluid bilayer of phospholipids.

Proteins bob around it which is the reason why it is called the Fluid Mosaic Model

Membrane Lipids - Fluid Part: Phospholipid

Responsible for the selective permeability of cell

Membrane Lipids - Fluid Part: Sterols

Maintain the membranes fluidity as the temperature fluctuates (Cholesterol in animal membranes)

Membrane Proteins - Mosaic Part: Integral Proteins

Proteins embedded within the membrane

Membrane Proteins - Mosaic Part: Peripheral proteins

Proteins bound to the surface of the membrane

Membrane Proteins - Mosaic Part: Lipid-Anchored Proteins

Proteins located on the surface of the cell membrane that are attached to the lipids within the cell membrane

Cell to Cell Recognition: Glycolipids

Carbohydrate groups attached to lipids

Cell to Cell Recognition: Glycoprotein

Carbohydrate groups attached to proteins for cell recognition

Membrane Proteins

Are classified according to their mode of attachment to the membrane as integral membrane proteins (a-d), peripheral membrane proteins (e), or lipid-anchored membrane proteins (f-g).

Functions of Membrane Proteins: Channel Proteins

Allows only one or a few types of specific molecules to move across
Ex: Aquaporins

Functions of Membrane Proteins: Carrier proteins

Moves substances across the membrane

changes shape as solutes pass through.

Functions of Membrane Proteins: Enzymatic Activity

Enzymatic proteins directly participate in metabolic reactions

Functions of Membrane Proteins: Adhesion Proteins

The junctions assist cell to cell adhesion and communication

Functions of Membrane Proteins: Glycoproteins

Enable our bodies to distinguish between our own cells and others

Functions of Membrane Proteins: Receptor Proteins

Has a shape that allows a specific molecule, called a signal molecule to bind to it.

Functions of Membrane Proteins: Attachment to the cytoskeleton and extracellular matrix (ECM)

Microfilaments of the cytoskeleton may be bound to membrane proteins to maintain cell shape and stabilize the location of certain membrane proteins.

Fluidity of Membrane

Membranes are not static sheets of molecules locked rigidly in place.

Do Membrane Proteins Move?

Movement of membrane proteins are slower compared to lipids and are restricted to a limited area of the membrane.

Factors Affecting Membrane Fluidity: Double Bonds

Because of the kinks in fatty acid chains where double bonds are located, unsaturated hydrocarbon tails cannot pack closely together, thus making the membrane more fluid

Factors Affecting Membrane Fluidity: Steroids

The steroid cholesterol, which is wedged between phospholipid molecules in the plasma membranes of animal cells, has different effects on membrane fluidity at different temperatures

Evolution of Differences in Membrane Lipid Composition

Extreme environments pose a challenge for life, resulting in evolutionary adaptations that include differences in membrane lipid composition.

Most Organisms can Regulate Membrane Fluidity

• Most organisms can regulate membrane fluidity, primarily by changing the lipid composition of their membranes.
• An ability that is important for "cold-blooded" organisms

Passive Transport

A substance moves across a membrane without the direct expenditure of energy.
• Diffusion, Facilitated Diffusion, and Osmosis

Facilitated diffusion is considered a passive transport because the solute is moving down its concentration gradient, a process that requires no energy.

Active Transport

A cell uses a transport protein to move a concentration substance against its gradient from where it is less concentrated to where it is more concentrated
• Sodium-Potassium Pump

Sodium-Potassium Pump

Cells must contain high concentrations of potassium (K+) and low concentrations of sodium (Na+) to perform many functions.

Other examples of active transport

In Plants :
● lons moving from soil into plant roots
● Minerals traveling through a stem to various parts of the plant
● Sugars from photosynthesis moving from leaves to fruit

In Animals :
● Amino acids moving along the human intestinal tract
● Glucose moving in or out of a cell
● Enzyme secretion
● Release of antibodies

Bulk Transport

Macromolecules are often too large to be moved by transport proteins, so vesicles are formed
(Use vesicles to transport substances)
• Endocytosis and Exocytosis

Simple Diffusion

Diffusion is the spontaneous movement of a substance from a region where it is more concentrated to a region where it is less concentrated.

Substances may enter or leave cells by simple diffusion only if they can pass freely through the membrane

Diffusion of one Solute

Diffusion also occurs across membranes.

Random movement of dye molecules will cause some to pass through the pores; this will happen more often on the side with more dye molecules.

Diffusion of two solutes

Note that each substance diffuses down its own concentration gradient, unaffected by the concentration gradients of other substances

Osmosis

Solvent molecules move from low to high solute concentration

Effects of Osmosis on Water Balance

Water diffuses across the membrane from the region of higher free water concentration (lower solute concentration) to that of lower free water concentration (higher solute concentration) until the solute concentrations on both sides of the membrane are more nearly equal.

Effects of Osmosis on Cells

Tonicity is the ability of a surrounding solution to cause a cell to gain or lose water.
● Hypo (less than)
● Iso (same as)
●Hyper (more than)

Effect of Osmosis on Animal Cells

There will be no net movement of water across the membrane
The cell is stable

The water inside the cell goes out.
The cell shrinks.

Water enters inside the cell faster than it leaves
The cell bursts.

Osmosis in Plant Cells

Hypo means less, meaning the solution outside the cell has LESSER solute than the one inside the cell

Iso means same, meaning the Hyper means more, meaning solution inside the cell is the solution outside the cell

similar or EQUAL to the has GREATER solute than the solution outside the cell one inside the cell

Phagocytosis

● Also known as cellular-eating
● Cell engulfs a particle by extending pseudopodia around it and packaging it within a membranous sac called a food vacuole.

Pinocytosis

• Also known as cell drinking
• This occurs when vesicles form around a liquid or around very small particles.

Receptor-Mediated Endocytosis

A form of endocytosis in which receptor proteins on the cell surface are used to capture a specific target molecule.

Biomolecules

Compounds can be classified into two types:
- Organic (living, proteins carbs, lipids, nucleic acid)
- Inorganic (non living, water, acid, bases, salts, co2)

Element

- the simplest form of substance that cannot be simplified into another form.
- Major elements that makeup living systems: Carbon, Hydrogen, Oxygen, Nitrogen, Phosphorus, Sulfur, Calcium

Compounds

a substance composed of two or more elements that are chemically combined together
Compounds in Living Systems: Inorganic & Organic

Inorganic Compounds

• any substance in which two or more chemical elements (usually other than carbon) are combined, nearly always in definite proportions
• water, acids, bases, electrolytes, carbon dioxide

Water

The Universal and Versatile Solvent
- Most common biological solvent, (dissolves an enormous variety of solutes necessary for living)
- Can exist in nature as solid, liquid, gaseous states

Characteristics of Water: Biological solvent

ability to dissolve many substances including essential molecules in the body

Characteristics of Water: High heat capacity

A large amount of heat is needed to increase the temperature. It helps in maintaining a constant body.

Characteristics of Water: High heat of vaporization

Helps in preventing dehydration in an organism

Characteristics of Water: High heat of fusion

helps organism from freezing at a low temperature

Characteristics of Water: Medium for chemical and physical processes

can serve as a place for exchanging gases and nutrients, and elimination of waste

Characteristics of Water: Means of transport

Can serve as a transporter/vehicle in the distribution of nutrients gases and collection of waste product all throughout the body

Acids

Taste sour, change the color of certain indicators
• react with some metals and bases
• promote chemical reactions (acid catalysis) in a water solution
• Ex: acetic acid, ascorbic acid, citric acid, carbonic acid, hydrochloric acid
• ptt: 2-4

Bases

• bitter, slippery in consistency
• turns litmus paper to blue
• i.e. sodium hydroxide, ammonium hydroxide, some antacids

pH Scale

used to describe the acidity and basicity of a solution. (6 and lower = more acidic, 7 - pure water, 8 and higher = more basic)

Electrolytes

● can conduct electricity within the body
● cations - positively charged
● anions – negatively charged
● important in maintaining voltages in cell membrane
• sends electrical impulses in nerve cells and muscle cells

Carbon Dioxide

● plants : important for photosynthesis
● animals : waste product from the breakdown of glucose
● a by-product in ethanol production (fermentation)

Organic Compounds

● contain carbon (except for carbon dioxide)
•● aka macromolecules - made up of hundreds or thousands of atoms
o individual units: monomers
● Types: proteins, carbohydrates, lipids, nucleic acid

Monomers of Biomolecules

Nucleic Acid, Carbohydrate, Lipid, & Protein

Proteins

• most abundant
• proteios (greek) - first place
• monomer: amino acids
• serve as gene activators, membrane receptors, transporter, clotting factors, etc.

Classes of Proteins: Structural proteins

- found in the hair of mammals
- makes up tendons and ligaments

Classes of Proteins: Contractile proteins

- provides muscular movement

Classes of Proteins: Storage proteins

- serve as biological reserves of metal ions & amino acids used by organisms

Classes of Proteins: Defensive proteins

- promote protection against foreign bodies
- antibodies

Classes of Proteins: Transport proteins

- serves the function of moving other materials within an organism
enzyme

Classes of Proteins: Signal proteins

- hormones, insulin, enkephalins
- communicates with the rest of the body w/o blood vessels

Enkephalins
- found in the thalamus; help moderate pain by suppressing pain signals in the brain.
Insulin
- produced by the pancreas; allows your body to use glucose for energy and store it for later use.
Thyroid hormones
- important for the proper development of brain, skeleton, and organs.

Enzyme

- serves as chemical catalyst, changes rate of reaction

Substrate

the substance on which an enzyme operates

Active site

proteins that help speed up metabolism, or the chemical reactions in our bodies

A GUIDE TO THE TWENTY COMMON AMINO ACIDS

Barone's Essential Amino Acid Mnemonic ^ PVT. TIM HALL ^

Primary structure

• shows the sequence of amino acids forming polypeptide chains
• attached together by covalent or peptide bonds done during translation
• one line of amino acids
• done via translation in protein synthesis

Secondary structure

• highly regular substructure
• can be alpha helix or beta strand
• defined by #/H bonds between the main chain peptide groups
• in a form of a helix

Tertiary structure

• overall 3D shape of polypeptide by a pattern of folding driven by hydrophobic interactions
• alpha helices and beta sheets are folded into a compact globule
• complicated

Quaternary structure

• arrangement of multiple folded protein or coiling protein molecules in a multi-subunit complex

Carbohydrates

• class molecules ranging from small sugar subunits to large polypeptides
• main source of energy for living organisms
• contains Carbon, Hydrogen, Oxygen
• groups : monosaccharide, disaccharide, polysaccharide

Monosaccharides

• Simple sugars
• 1 sugar unit
• glucose, fructose, galactose
• serve as starting material for some organic molecules such as fat

Disaccharide

• complex sugar
• made up of 2 molecules joined together
• sucrose (glucose fructose), maltose (glucose2), lactose (galactose glucose)

Polysaccharides

• complex sugar
• made up of chains/branches of monosaccharide
• storage and structure
• examples: starches

Lipids

• from lipos (greek) - fat
• includes fats and fat-like substances (phospholipid, wax, steroid, etc.)
• consists of Carbon, Hydrogen, & Oxygen

Functions of lipids

- store and produce energy
- serve as insulation to prevent heat loss
- protect against extreme cold
- serve as solvent for fat-soluble vitamins and hormones
- prevent water loss in skin

Types of fatty acid

• unsaturated
- liquid at room temperature
- found mostly in plants
- has a double bond
- healthier
•saturated
- solid at room temperature
- mostly found in animals
- no double bonds

Other examples of lipids

• Wax
• Phospholipids
• steroids

Wax

- solid of room temperature
- high melting point
- hydrophobic
• plants: protective structure
• animals: skin and fur maintenance
• humans: produced by glands in the outer ear canal

Phospholipids

- a major component of cell membrane
- 2 fatty acids + 1 phosphate group
- responsible for the polar and non-polar characteristics of cell membrane

Steroids

- hydrophobic and insoluble in water, don't resemble lipids since they have -
- a structure composed of four fused rings
- cholesterol most common steroid

Nucleic acid

- serves as genetic information storage molecule
- provide info to make proteins
- monomer: nucleotide
- types: RNA, DNA

When a phosphate group is broken off the tail of an ATP molecule
(by hydrolysis) the molecule becomes ADP (adenosine
diphosphate). That hydrolysis is an exergonic reaction and it yields
energy. The bonds holding the phosphate onto ATP are weak.

Difference of DNA & RNA

DNA is a double-stranded molecule that has a long chain
of nucleotides. RNA is a single-stranded molecule which
has a shorter chain of nucleotides. DNA replicates on its
own, it is self-replicating. RNA does not replicate on its
own.