Cell Membrane Proteins & Carbohydrates

Cell membranes - Protein Function

• Proteins within cell membranes perform multiple functions
• Transport of molecules across membrane
• Enzymes catalyze reactions
• Signaling involves proteins binding to chemicals, triggering changes on the inner surface
• Attachment points for cytoskeleton
• Some proteins recognize microbes for immune response

Integral Membrane Proteins

• Integral membrane proteins are embedded within the membrane
• At least one region is anchored in the hydrophobic core
• Some go part of the way through the membrane
• Transmembrane proteins span the entire membrane

Peripheral Membrane Proteins

• Found on either the inner or outer surface
• Do not touch the hydrophobic core
• Mainly located on the cytosol side
• Part of the cytoskeleton

Carbohydrates

• Carbohydrates are attached to the protein outer surface
• Glycoproteins are bound to a protein
• Glycolipids are bound to a lipid
• Cellular markers enable cell recognition, signaling and immune responses

Components of Cell Membranes:

• Phospholipids form the bilayer, and provide a semi-permeable barrier with the main structural component of the bilayer
• Cholesterol maintains membrane fluidity and stability, embedded within the phospholipid bilayer
• Integral proteins transport molecules, act as receptors, and catalyze enzyme activities. They span the entire membrane (transmembrane)
• Peripheral proteins provide structural support and signal transduction, attached to either membrane surface (inner or outer)
• Carbohydrates enable cell recognition and signaling, also aid adhension and are attached to proteins (glycoproteins) or lipids (glycolipids)

Functions of Membrane Proteins:

• Transport: Facilitate the movement of charged or large substances across the membrane
• Attachment and Recognition: intracellular surface attachment to cytoskeleton, extracellular attachment sites to enable cell to cell recognition)
• Receptor for Signaling: Binds hormones or growth factors, triggering cellular reactions upon binding
• Enzymatic Activities: Catalyzing biochemical reactions.

Cell Membrane Function:

• Responsible for regulating what enters and exits the cell
• Facilitates nutrient intake and waste removal
• Used for cellular communication

Cell Membrane Structure:

• Primarily composed of a phospholipid bilayer (two layers)
• Includes hydrophilic heads that attract and are soluble in water
• Includes hydrophobic tails that repel and are insoluble in water

Main Components of Cell Membranes:

• Lipids: The primary structural component
• Proteins: Facilitate transport across the membrane
• Carbohydrates: Involved in communication

Phospholipids:

• Have a hydrophilic head which is negatively charged
• A phosphate group makes the head polar
• The head faces outwards due to the presence of water

Reason for Structure:

• Water is present both inside and outside of the cell
• Only hydrophilic heads are in contact with water
• Hydrophobic tails avoid contact with water and block substances from passing through

Membrane Fluidity:

• Saturated fatty acid tails pack tightly together making the membrane more dense typically with cooler temperatures
• Unsaturated fatty acid tails have kinks from double bonds that prevent tight packing, keeping the membrane fluid even at room temperature

Cholesterol:

• Found alongside membrane phospholipids
• Acts as a membrane stabilizer
• Minimizes the effects of temperature, keeping phospholipids from packing at low temperatures

Types of Nucleic Acids:

• DNA (deoxyribonucleic acid) and RNA (ribonucleic acid)

Notes and Functions:

• Nucleic acids are the genetic material in cells that determine genes and heredity

Nucleic Acid Monomers:

• DNA is composed of repeating nucleotides
• Nucleotides contain a sugar, a nitrogenous base, and a phosphate group

Pentose Sugars:

• DNA contains deoxyribose
• Deoxyribose is missing an oxygen atom
• RNA contains ribose
• Ribose is not missing an oxygen atom

Nitrogenous Bases:

• Divided into purines (two rings) and pyrimidines (one ring)
• Purines: Adenine (DNA, RNA) and Guanine (DNA, RNA)
• Pyrimidines: Cytosine (DNA, RNA), Thymine (DNA), and Uracil (RNA)

DNA Building Blocks:

• Consist of a phosphate group, deoxyribose sugar, and a nitrogenous base (adenine, thymine, cytosine, or guanine)

Phosphate in DNA:

• Exists as phosphoric acid or phosphate ion in solution

Nitrogenous Bases and Bonds:

• Guanine (G) pairs with Cytosine (C)
• Adenine (A) pairs with Thymine (T) in DNA
• Adenine (A) pairs with Uracil (U) in RNA

Phospholipids:

• Characterized by a hydrophilic head and hydrophobic tails

Cell Membranes:

• Phosphate group of phospholipids is hydrophilic (water-loving and polar)
• Fatty acid tails of phospholipids are hydrophobic (water-hating and non-polar)

Steroids:

• Signaling molecules
• Contain four fused hydrocarbon rings and several different functional groups

Waxes:

• Long-chain fatty acids with the formula C25-31H51-63O-C30-32H61-65

Characteristics & Content of Proteins:

• Keratin, muscles, hormones, enzymes, channels, and oxygen transporters
• Contains carbon, hydrogen, oxygen, nitrogen, and sometimes sulfur/phosphorus
• Made of long chains of amino acids

Amino Acids:

• R group (radical) makes each amino acid different
• Depending on R, the amino acids will have different properties
• Humans need 20 amino acids
• Body cannot produce 9 essential amino acids so they must come from diet

Bonding:

Carboxyl group bonds with amino group of the other amino acid

• Dehydration (Condensation) reaction because water is released
• Peptide bond

Polypeptides:

• Building: Make larger proteins
• Two amino acids means dipeptide is formed
• Three or more amino acids means polypeptide is formed
• Breaking: Broken using a hydrolysis reaction (add water)

Protein Structure:

• Levels:
  • PRIMARY Sequence of amino acids to form a polypeptide
  • SECONDARY Polypeptides coil into alpha helices or loop into beta sheets
  • TERTIARY further coiling into specific shape
  • QUATERNARY multiple polypeptides interacting

Lipids:

• Fats
• Phospholipids
• Steroids and Waxes

Functions of Lipids:

• Storage
• Fats
• Insulation
• Blubber in animals in cold climates, penguins, and whales
• Energy
• More energy than carbs
• Cell Membranes
• Phospholipids

Fats and Oils:

• Generally made from triglycerides
• One glycerol molecule and three fatty acids make up a triglyceride

Triglyceride Synthesis:

• Condensation reaction where dehydration occurs as an ester linkage forms between glycerol hydroxyl and the carboxyl on fatty acid

Phospholipids:

• Main structural component of cell membranes
  • One glycerol
  • Two fatty acids
  • Phosphate group

Monosaccharides:

• Simple sugars such as sweet sugars
• Used for quick energy

Major Types:

• Pentose sugars (n=5) such as nucleic acids (DNA)
• Hexose sugars (n=6) such as C6H12O6 (glucose, fructose, galactose)

Structure:

• Every carbon is attached to an oxygen
• One carbon is double bonded to an oxygen (carbonyl)
• All other carbons are bonded to an alcohol (hydroxyl)
• Making them polar and soluble in water

Pentose Sugars:

• Glucose, fructose, galactose
• Linear when in a dry state
• Forms rings when dissolved into water

Glucose Isomers:

• Alpha: OH is below
• Beta: OH is above

Organic Compounds:

Carbohydrates, lipids, proteins, and nucleic acids

Macromolecules:

• Large molecules made of repeating units
  • Monomer = A single unit
  • Polymer = Large units made by bonded monomers

Functional Groups:

• Hydroxyl (-OH, carbohydrates)
• Carbonyl (>C=O, proteins)
• Carboxyl (-C=OOH amino)
• Amino (-N-H, proteins)
• Phosphate (O-P-O-O, DNA, ATP) H

Carbohydrates:

• Carbon
  • Bond creation
  • Tetrahedral bonds
  • Organic molecule of carbon, hydrogen, oxygen
  • 1:2:1 ratio
  • Three saccaride groups

Monosaccharides:

• Two monosaccharides that link Glucose + Glucose to make Maltose Glucose + fructose = sucrose
• Glucose + galactose = lactose

Polysaccharides:

• Many monosaccharides via condensation
• Easily broken down into glucose
• Starch, glycogen and cellulose

Carbohydrates Functionality:

• Carbon based, each carbon can make four bonds, typically making a tetrahedral
• Organic molecule of carbon, hydrogen, and oxygen
• Typically has a 1:2:1 ratio
• N = number of carbon atoms/molecules
• Exist as saccharides like monosaccharides, disaccharides and polysaccharide

Functional Groups:

• Are reactive portions of an organic molecule and give the molecule polarity
• Types include
  • Carbo (monosaccharides, disaccharides, polysaccharides)
  • Proteins (amino acids)
  • Lipids (fatty acids, glycerol, sterols, waxes)
  • Nucleic acid (nucleotides)

Review of Carbohydrates:

• Monomers are small and single units that are the building blocks
• Polymers are larger multiple units
  • Alpha glucose involves hydrogen ABOVE carbon
  • Beta glucose = hydrogen is BELOW carbon
• Glycosidic bonds form when two monomers bond, resulting in condensation through dehydration.
• If you add hydrolysis is when water is added and breaks the bonds to make smaller structures

Proteins:

• Are building blocks in 20 varieties of amino acids that make up amino acid monomers
• Amino, carboxyl and R groups determine the kind of an amino acid.
• Peptide bonds link amino acids releasing a water molecule and undergoing dehydration in a synthesis reaction

Enzymes: Activity and Functions

• Enzymes function within a narrow pH range and can denature when out of acceptable range
• Enzyme activity decreases and ionic bonding is disrupted and denatured because altering it can cause 3D changes
• Enzymes also function at certain substrate concentrations
• As substrate concentration increases at an initial rate, but when enzymes all occupy active sites they limit reaction rate
• Enzyme concentration can also effect the rate of reaction at high levels of substrate (the reaction rate increases linearly when enzymatic concentration rises)

Enzyme Mechanisms and Regulation:

• Lock and Key Model: Enzymes have a complementary shape to the substrate
• Induced Fit: enzymes mold during the substrate and regulation of activity with inhibitors, such as with competitive molecules
• Competitive Enzyme Inhibition: Resembles and Substrates compete for the active site and stops the reaction
• Non-Competitive Inhibition: An inhibitor that binds to and alters an enzymes non-active site to change its shape and can either be reversible or non-reversible and damaging it (denaturing)

Enzyme Feedback Inhibitors:

• Produce excessive product molecules that act as non-competitive inhibitors, stopping the reaction or pathway from proceeding and saving resources

Enzyme Notes and Functions:

• Enzymes speed up chemical reactions
• Allows reactions at lower temperatures
• Speeds up reactions, is not involved
• Enzymes are proteins
• Proteases (proteins),
• Lipases (fats), and amylases (carbs)

Metabolism:

• Anabolic reactions build new chemicals and Catatonic reactions break down substances and all come the metabolic chain
• Metabolic reactions:
  • Condensation: Small to big / synthesis/anabolic reaction

Reactions:

• Hydrolysis/Digestion/Catabolic breakdown: Big to small
• Metabolic : exergonic releases more energy than used/Digestion
• Endergonic reactions absorb more energy than released

Biochemical reactions and Energy:

• Activation energy needed to destabilize the bonds of a molecule and the amount from reactant to the maximum point

Enzymes:

• Enymes reduce the amount of activation energy
• Biological catalysts
• Consist of globular proteins (polymer of amino acides)
• Long chains that fold into unigue 3D structures
• Substrate is a reactant which binds to the enzyme and result that fits into the enzymes catalytic site
• Enzyme substrate complex complex formed

Properties:

• Enzymes are reaction specific due to bonds but remain unnaffacted/unaltered
• Cell conditions and temperature/pH can affect it
• Increased Temp = higher reaction rate due to kinetic enery and collisions with substrates
• Overheating is dangerous and results in losses of 2D/3D structures, breaking bonds and shape means you loose binding and cannot react