Carbohydrates

• Carbohydrates or sugars, are macromolecules that play an important role in energy, contribute to cell structure, and are involved with cell recognition and identity
• Carbohydrates include monosaccharide ("one-sugar") monomers, oligosaccharide ("few-sugars") small polymers, polysaccharide ("many-sugars") large polymers

Carbohydrate Formula

• Carbohydrates have the molecular formula (CH2O)n where "Carbo" refers to carbon, "Hydrate" refers to water, and "n" can vary from 3 to over a thousand
• Carbohydrates contain a carbonyl group (C=O), hydroxyl groups (O-H), and many carbon-hydrogen bonds (C-H)
• Since carbonyl and hydroxyl groups are polar, carbohydrates are hydrophilic

Monosaccharides

• Monosaccharide monomers are simple sugars that structurally vary in four primary ways:
• Location of the carbonyl group
• Location of the hydroxyl group
• Number of carbon atoms present
• Linear and alternative ring forms

Carbonyl Group

• Aldose: Carbonyl group is found at the end of the monosaccharide e.g. glucose
• Ketose: Carbonyl group is found in the middle of the monosaccharide e.g. fructose

Number of Carbons

• Triose: Three e.g. glyceraldehyde
• Pentose: Five e.g. ribose
• Hexose: Six e.g. glucose

Disaccharides

• Polysaccharides are complex carbohydrates; polymers of monosaccharide monomers
• The simplest polysaccharides are disaccharides, comprised of two monosaccharide monomers, that can be identical or different
• Sucrose is made of glucose and fructose
• Lactose is made of glucose and galactose
• Maltose is made of glucoses

Glycosidic Linkages

• Glycosidic Linkages linkages can form between any two hydroxyl groups, so the location and geometry of these bonds vary widely
• Two of most common linkages: α-1,4-glycosidic linkage and β-1,4- glycosidic linkage
• Both linkages are between the C-1 & C-4 carbons however, their geometry is different and C-1 hydroxyl groups are on opposite sides of the plane of the glucose rings

Plant Starches

• Plants store sugar as starch as polymers of monosaccharide monomers found in organisms today
• Composed of α-glucose monomers, it forms a helix
• Amylose is unbranched starch with only α-1,4-glycosidic linkages
• Amylopectin is branched starch with some α-1,6-glycosidic linkages
• Branches occur about once in every 30 monomers

Animal Starches

• Animals store sugar as glycogen, which is stored in liver and muscle cells
• Glycogen can be broken into α-glucose monomers for energy
• Glycogen is a highly branched α-glucose polymer, nearly identical to starch
• Branches occur in about 1 out of 10 monomers

Cellulose

• Cellulose is a structural polymer in plants that forms a protective layer around plant cells called the cell wall
• It is made of β-glucose monomers joined by β-1,4-glycosidic linkage and every other glucose is flipped
• This generates a linear molecule rather than a helix, which permits hydrogen bonds to form between adjacent, parallel strands

Chitin

• Chitin is a structural polymer found in cell walls of fungi, some algae and exoskeletons of insects and crustaceans
• The monomer is N-acetylglucosamine (NAG) with a structure similar to cellulose
• Made of ẞ-1,4-glycosidic linkages with every other monomer flipped producing linear strands with hydrogen bonds between them

Peptidoglycan

• Peptidoglycan is a structural polymer found in bacterial cell walls
• It has long backbones of alternating monosaccharides joined by β-1,4-glycosidic linkages
• Short amino acid chains form peptide bonds between adjacent strands

Carbohydrate Functions

• Carbohydrates have diverse functions in cells such as precursors to larger molecules, fibrous structural materials, indicate cell identity, and store chemical energy
• Sugars frequently are the raw “carbon skeletons" are used as building blocks in the synthesis of important molecules, like amino acids

Provide Structural Support:

• Cellulose, Chitin, and Peptidoglycan form long strands with bonds between adjacent strands that may be organized into fibres or layered in sheets
• These structures give cells and organisms great strength and elasticity
• β-1,4-glycosidic linkages are not easy to hydrolyze because most organisms lack enzymes to hydrolyze them and these fibres exclude water, making hydrolysis difficult
• Carbohydrates form dietary fibre- important for digestive health

Indicate Cell Identity:

• Although polysaccharides are unable to store information they do display information on the outer surface of cells like Glycoproteins -carbohydrates covalently attached to proteins and Glycolipids carbohydrates covalently attached to lipids
• Glycoproteins and glycolipids molecules are used in cell-cell recognition tasks, including:
  • Identify cells as "self"
  • Eg. A, B, O blood antigens
  • Eg. Major histocompatibility complex (MHC) antigens
  • Cell-cell signalling: Communication between cells

Store Chemical Energy:

• Carbohydrates store and provide chemical energy in cells
• In chemical evolution, the kinetic energy of sunlight and heat were converted into chemical energy stored in the bonds of formaldehyde (H₂CO) and hydrogen cyanide (HCN)
• In photosynthesis, plants harvest energy from sunlight and store it in the bonds of carbohydrates via the following reaction:. CO2 + H2O + sunlight → (CH₂O)n + O2
• Electrons in C–H and C–C bonds are shared more equally and have higher potential energy making them more energetic than Carbohydrates from CO2

Starch and Glycogen

• Starch and glycogen are easily hydrolyzed because they have α-glycosidic linkages
• The hydrolysis of α-glycosidic linkages in glycogen is catalyzed by the enzyme phosphorylase. Most animal cells contain phosphorylase to readily break down glycogen to provide glucose
• The α-glycosidic linkages in starch are hydrolyzed by amylase enzymes. Amylases play a key role in carbohydrate digestion

Energy Storage

• When a cell needs energy, carbohydrates participate in exergonic reactions that synthesize adenosine triphosphate (ATP):
• CH2O + O2 + ADP + Pi → CO2 + H2O + ATP
• The free energy in ATP can be used to drive endergonic reactions and perform cell work
• Carbohydrates contain a large number of C-H bonds, which have high free energy
• Fatty acids contain even more C-H bonds and consequently more free energy than carbohydrates

Natural Sweeteners

• Humans have taste receptors (TAS1R3) for sweetness telling us a food is high in energy
• A common sweetener, glucose-fructose (a.k.a. high fructose corn syrup) is often found in many processed foods
• High fructose corn syrup is manufactured by converting starch to glucose, then some glucose is converted to fructose because fructose is sweeter, so the mixture of glucose/fructose is both sweeter and cheaper that sucrose

Artificial Sweeteners

• Health issues have occurred with artificial sweeteners because they are excreted instead of metabolized except for Aspartame, that breaks down into methanol and aspartic acid, that are dangerous for individuals with PKU
• But generally, Health Canada has tested these sweeteners and determined they are safe for most people and do not help you lose weight, instead your health comes from eating a sensible diet

Membrane Importance

• The plasma membrane, or cell membrane, separates life from nonlife, seperates the cell's interior from the external environment and functions to keep damaging materials out, facilitates chemical reactions, and allow other molecules to enter

Lipids

• Lipids consist of carbon-containing compounds commonly found in organisms that are largely nonpolar and hydrophobic
• Hydrocarbons are molecules that contain primarily C and H that are nonpolar and hydrophobic; electrons are shared equally in C–H bonds
• A fatty acid is a hydrocarbon chain of containing 14-20 carbons atoms bonded to a carboxyl (-COOH) functional group and can be saturated or unsaturated

Lipid Structure

• Lipid structure is characterized by a physical property, their insolubility in water instead of a shared chemical structure
• This insolubility is based on the high proportion of nonpolar C-C and C-H bonds relative to polar functional groups

Important Lipids

• Fats: composed of three fatty acids linked to glycerol, also called triacylglycerols / triglycerides
• Steroids: a family of lipids with a distinctive fou ring structure, such as Cholesterol that is an important steroid in mammals
• Phospholipids: consist of a glycerol linked to a phosphate group and either consist of two chains of isoprene or two fatty acids

Fats/ Triacylglycerols

• Fats composed of 3 fatty acids linked to glycerol called triacylglycerols or triglycerides
• Fats that consist of polyunsaturated fatty acids are liquid and are called forms oils
• The primary role of fats is energy storage are formed by dehydration between the hydroxyl group of glycerol, and the carboxyl group of fatty acids (ester linkage)

Steroids

• Steroids are distinguished by a bulky, and bulky, four-ring structure
• They differs from one another by the functional groups attached to carbons in the rings,
• Some example include hormones such as estrogen and testosterone and cholesterol

Phospholipids

• Consist of a glycerol and a phosphate group bonded to a charged / polar molecule containing hydrocarbon chains
• They are amphipathic, "heads" consisting of a glycerol, phosphate, and a charged group containing highly polar covalent bonds
• They also consist of nonpolar fatty acid or isoprene chains; the "tail"
• The primary role of phospholipids is to form cell membranes

Phospholipid Placement in Water

• The hydrophilic phospholipid heads interact with water while the hydrophobic tails interact with each other

Phospholipid reactions to Water

• Phospholipids do not dissolve when they are placed in water
• When put into contact with water, phospholipids form either micelle or bilayer due to heads facing the water and tails facing each other and are formed spontaneously with no outside help
• Phospholipids tend to form phospholipid bilayers where two sheets align, hydrophilic "heads" face the water and hydrophobic "tails" face each other
• When lipid bilayers in water are agitated by shaking, the layers break and re-form as small, spherical structures called liposomes

Planar Blayers

• Researchers use them to conduct experinments on membran permeability
• Common questions include what happens when a known ion or molecule is added to one side of a lipid bilayer?

Lipid Permeability Factors

• Small molecules move across easily to allow passive transport
• The number of double bonds between the carbons in the phospholipid's hydrophobic tail: Double chain bonds can cause a kink, which makes it more permeable
• Unsaturated Hydrocarbons Have At Least 1 Double bond
• Saturated Hydrocarbons Does not contain any dounle bonds
• Length of the hydrocarbon tail: The longer the higher permeability
• The number of cholesterol molecules
• Temperature: Membrane fluidity decreases as temp drops

Affect of Double Bonds

• Membrane fluidity/ permeability increases with unsaturateds hydrocarbons with kinks in the tails
• Membrane fluidity/ permeability decreases with saturated hydrocarnons containing no kinks

Membrane Fluidity

• Individual phospholipids can move laterally throughout the lipid bilayer but rarely flip and is depended on temprature
• Quick molecule movement in membranes is a function of temperature/the structure of hydrocarbon tails and allows for membranes to:
  • Flexible - Cells can change shape
  • Repairable - Lipids move to reform a continuous surface
  • Expandable - Cells increase surface area by adding new membrane lipids

Lipids in Diet

• Most of the food we eat contains lipids that can come from
• cholesterol (essential for membrane fluidity and synthesis of hormones),
• Un- Saturated/monosaturated oil
• Saturated fats/processed food (trans fat/are the worst for you) in moderation

Substance Movement

• Small molecules/ions in solution called (solutes)
• They have thermal/kinetic energy
• The Random movement is called diffusion
• Active Transport & Passive Transport are the two ways materials come across a membrane

Diffusion

• A concentration gradient is created by a solute concentration
• Diffusion moves material from low to high
• Is spontanious w/ more antropy

Equilibrium

• Molecules ions are randomly distributed
• Molecules are still moving randomly
• There is no "net" movement

Osmosis

• Movement of water w/ unequal concentrations on membrane
• A selectivity permeable membrane moves more water to the other concentration
• Water moves from a low concentration to a high concentration
• This dilutes the higher concentration- balances the concentrations on both the sides of the layers

Tonicity

• Hypertonic: The concentration of a solution outside a cell contains a higher gradient
• Hypnotic: The concentration of a solution outside a cell contains a lower gradient
• Isotonic= The concentration of a solution where all cells are equal in gradient

Membrane Proteins

• Are amphipathic that can span membranes
• Some segments face both the interior/ exterior of the surfaces
• Are integral proteins that span through the membrane

Trans Membrane Proteins/ Functions

• Integral proteins that span
• Transport of selective ions/molecules in plasma membranes
• Effect membrane permeability

Peripheral Membrane Proteins

• Does not pass through it
• Interior/Exterior
• Often attached to integral proteins

Model of Membrane

• Sandwich: a. Hydrophilic proteins coat both sides of pure lipid membrane
• Fluid Mosaic: b. Some proteins are inserted with a lipid bilayer
• Best explanation is combination of both

Freeze Fracture Microscopy

• The surface of PM is visualized
• Images are consistent with fluid mosaic model

Methods to study membrane proteins

• Methods to Study: Detergent (amphipathic molecule)
• Detergent breaks up plasma membranes
• Coats hydrophobic in transmembrane
• Proteins are isolated by gel electrophoresis

Transport Proteins & Broad classes

• a. Channels b. Carrier proteins/transporters C. Pumps
• These are selective

Aquaporins

• Water pores
• Gate to open
• Open/Close in response to signal (Change in Electrical)
• Small molecules are carefully
• They are carefully controleld

Facilitated Diffusion

• facilitated diffusion. In that context, the movement of specific molecules from an area of high concentration to an area of low concentration through the help of a transport protein

Pumps Transport

• Transport molecule/energy against gradient
• Can also move gradient
• This gradient provides high concentration

Carbohydrates or sugars are macromolecules that play an important role in energy. They contribute to cell structure and are involved with cell recognition and identity. Carbohydrates include monosaccharide monomers, oligosaccharide small polymers, and polysaccharide large polymers.