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
- 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
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)
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 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
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
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
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.
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
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
Macromolecules are often too large to be moved by transport proteins, so vesicles are formed
(Use vesicles to transport substances)
• Endocytosis and Exocytosis
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
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
● 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.
• Also known as cell drinking
• This occurs when vesicles form around a liquid or around very small particles.
A form of endocytosis in which receptor proteins on the cell surface are used to capture a specific target molecule.
Compounds can be classified into two types:
- Organic (living, proteins carbs, lipids, nucleic acid)
- Inorganic (non living, water, acid, bases, salts, co2)
- 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
a substance composed of two or more elements that are chemically combined together
Compounds in Living Systems: Inorganic & Organic
• 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
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
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
• bitter, slippery in consistency
• turns litmus paper to blue
• i.e. sodium hydroxide, ammonium hydroxide, some antacids
used to describe the acidity and basicity of a solution. (6 and lower = more acidic, 7 - pure water, 8 and higher = more basic)
● 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
● plants : important for photosynthesis
● animals : waste product from the breakdown of glucose
● a by-product in ethanol production (fermentation)
● 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
• 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
Classes of Proteins: Transport proteins
- serves the function of moving other materials within an organism
Classes of Proteins: Signal proteins
- hormones, insulin, enkephalins
- communicates with the rest of the body w/o blood vessels
- found in the thalamus; help moderate pain by suppressing pain signals in the brain.
- produced by the pancreas; allows your body to use glucose for energy and store it for later use.
- important for the proper development of brain, skeleton, and organs.
- serves as chemical catalyst, changes rate of reaction
the substance on which an enzyme operates
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 ^
• 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
• 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
• 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
• arrangement of multiple folded protein or coiling protein molecules in a multi-subunit complex
• 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
• Simple sugars
• 1 sugar unit
• glucose, fructose, galactose
• serve as starting material for some organic molecules such as fat
• complex sugar
• made up of 2 molecules joined together
• sucrose (glucose fructose), maltose (glucose2), lactose (galactose glucose)
• complex sugar
• made up of chains/branches of monosaccharide
• storage and structure
• examples: starches
• 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
- liquid at room temperature
- found mostly in plants
- has a double bond
- solid at room temperature
- mostly found in animals
- no double bonds
Other examples of lipids
- solid of room temperature
- high melting point
• plants: protective structure
• animals: skin and fur maintenance
• humans: produced by glands in the outer ear canal
- a major component of cell membrane
- 2 fatty acids + 1 phosphate group
- responsible for the polar and non-polar characteristics of cell membrane
- hydrophobic and insoluble in water, don't resemble lipids since they have -
- a structure composed of four fused rings
- cholesterol most common steroid
- 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