B1.1 Carbohydrates and Lipids

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Outline the number and type of bonds carbon can form with other atoms.

• Carbon can form 4 covalent bonds with other non-metals

• This allows its compounds stability and a large diversity

Outline the cause and consequence of covalent bonds between atoms.

• Covalent bonds form between non-metals in which the atoms of these elements share electrons

• They do this in order to obtain an octet, a full and stable outer shell

• This results in various, stable and diverse compounds

List the four major classes of carbon compounds used by living organisms.

• Nucleic Acids

• Lipids

• Carbohydrates

• Proteins

List examples of branched chain. unbranched chain, single chain, multiple chain

Branched Chain Carbohydrates

1. Glycogen:

   • Found in animals, particularly in liver and muscle cells.

   • Highly branched structure allows for rapid release of glucose when energy is needed.

2. Starch (Amylopectin):

   • A major storage polysaccharide in plants.

   • Composed of glucose units with a branched structure, making it more accessible for enzymatic breakdown.

Unbranched Chain Carbohydrates

1. Cellulose:

   • A structural polysaccharide found in plant cell walls.

   • Composed of long, unbranched chains of beta-glucose molecules linked by beta-1,4-glycosidic bonds.

   • Provides rigidity and strength to plant cell walls.

2. Starch (Amylose):

   • Another component of starch in plants.

   • Composed of unbranched chains of alpha-glucose molecules linked by alpha-1,4-glycosidic bonds.

   • Forms a helical structure, making it less accessible to enzymes compared to amylopectin.

Single Chain Carbohydrates

1. Maltose:

   • A disaccharide consisting of two glucose molecules linked by an alpha-1,4-glycosidic bond.

   • An intermediate in the digestion of starch.

2. Lactose:

   • A disaccharide composed of glucose and galactose linked by a beta-1,4-glycosidic bond.

   • Found in milk and dairy products.

3. Sucrose:

   • A disaccharide composed of glucose and fructose linked by an alpha-1,2-glycosidic bond.

   • Commonly known as table sugar, used by plants for transport and storage of energy.

Multiple Chain Carbohydrates

1. Glycoproteins:

   • Proteins with carbohydrate chains attached.

   • Multiple carbohydrate chains of varying lengths and branching patterns.

   • Involved in cell-cell recognition, signaling, and immune responses.

2. Proteoglycans:

   • Consist of a core protein with many long, linear carbohydrate chains (glycosaminoglycans) attached.

   • Found in the extracellular matrix, providing structural support and mediating cell signaling.

3. Hemagglutinin:

   • A glycoprotein found on the surface of the influenza virus.

   • Contains multiple carbohydrate chains that help in virus attachment to host cells.

Define monomer and polymer.

• smaller, recurring subunits that link together to form macromolecules

• polymers are larger structures made up of monomers by strong chemical bonds

Describe condensation reactions.

• a chemical reaction in which two molecules join, one molecule’s hydroxyl group (-OH) and the other’s hydrogen atom (-H) join as well, resulting in the formation of a new polymer, but the loss of an H2O molecule

• this is how most biological molecules form

What is crucial for condensation reactions to take place?

• two molecules with two different functional groups

Outline the condensation reactions that form polysaccharides, polypeptides and nucleic acids.

Polysaccharides:

1. Monosaccharide Subunits:

   • Polysaccharides are polymers composed of monosaccharide subunits, such as glucose, fructose, and galactose.

2. Condensation Reaction:

   • Condensation reactions, also known as dehydration synthesis, occur between two monosaccharide molecules.

   • During condensation, a hydroxyl (-OH) group from one monosaccharide and a hydrogen atom from the other are removed, forming a covalent bond called a glycosidic bond.

   • This process releases a molecule of water.

3. Polymerization:

   • The repeated condensation reactions result in the polymerization of monosaccharides into polysaccharides.

   • Examples include the formation of:

     • Glycogen from glucose monomers.

     • Starch from glucose monomers.

     • Cellulose from beta-glucose monomers.

Polypeptides:

1. Amino Acid Subunits:

   • Polypeptides are polymers composed of amino acid subunits.

2. Condensation Reaction:

   • Condensation reactions occur between the amino group (-NH2) of one amino acid and the carboxyl group (-COOH) of another amino acid.

   • During condensation, a water molecule is removed, and the amino and carboxyl groups combine to form a peptide bond.

   • This process releases a molecule of water.

3. Polymerization:

   • Sequential condensation reactions link amino acids together, forming a linear chain known as a polypeptide.

   • The sequence of amino acids is determined by the genetic code.

Nucleic Acids:

1. Nucleotide Subunits:

   • Nucleic acids, such as DNA and RNA, are polymers composed of nucleotide subunits.

2. Condensation Reaction:

   • Condensation reactions occur between the phosphate group of one nucleotide and the hydroxyl group of the sugar (ribose or deoxyribose) of another nucleotide.

   • During condensation, a water molecule is removed, and a phosphodiester bond forms between the phosphate and sugar groups.

   • This process releases a molecule of water.

3. Polymerization:

   • Sequential condensation reactions link nucleotides together, forming a linear chain.

   • In DNA, the sugar-phosphate backbone is formed by phosphodiester bonds between the 3' carbon of one sugar and the 5' carbon of the next.

   • The sequence of nucleotides carries genetic information.

Describe hydrolysis reactions.

• Hydrolysis is a chemical reaction in which water molecules are used to break the covalent bonds between the monomers that make a polymer

• Doing so the polymers are split into individual monomers which are ready for biological processes

Outline the hydrolysis reactions that digest polysaccharides, polypeptides and nucleic acids.

Polysaccharides:

1. Polysaccharide Substrate:

   • Polysaccharides such as glycogen, starch, and cellulose are complex carbohydrates composed of long chains of monosaccharide subunits.

2. Hydrolysis Reaction:

   • Hydrolysis reactions involve the cleavage of covalent bonds in a molecule using water.

   • In the digestion of polysaccharides, enzymes called glycosidases catalyze hydrolysis reactions.

   • Glycosidases break the glycosidic bonds between monosaccharide subunits by adding a water molecule.

   • The water molecule donates a hydroxyl group to one monosaccharide unit and a hydrogen ion to the adjacent unit, breaking the bond.

3. Product Formation:

   • The hydrolysis of polysaccharides results in the formation of monosaccharides or disaccharides, depending on the degree of polymerization.

   • For example, the hydrolysis of glycogen and starch yields glucose molecules, while the hydrolysis of cellulose yields glucose molecules or cellobiose (a disaccharide of glucose).

Polypeptides:

1. Polypeptide Substrate:

   • Polypeptides are long chains of amino acids linked by peptide bonds.

2. Hydrolysis Reaction:

   • Hydrolysis reactions in protein digestion are catalyzed by enzymes called proteases.

   • Proteases cleave peptide bonds between amino acids by adding a water molecule.

   • The water molecule donates a hydroxyl group to the carbonyl carbon of one amino acid and a hydrogen ion to the nitrogen of the adjacent amino acid, breaking the peptide bond.

3. Product Formation:

   • The hydrolysis of polypeptides results in the formation of shorter peptides, dipeptides, or free amino acids.

   • Further hydrolysis of peptides yields individual amino acids, which can be absorbed and utilized by cells for protein synthesis or energy.

Nucleic Acids:

1. Nucleic Acid Substrate:

   • Nucleic acids such as DNA and RNA are composed of nucleotide monomers.

2. Hydrolysis Reaction:

   • Hydrolysis reactions in nucleic acid digestion are catalyzed by enzymes called nucleases.

   • Nucleases cleave phosphodiester bonds between nucleotides by adding a water molecule.

   • The water molecule donates a hydroxyl group to one phosphate group and a hydrogen ion to the adjacent phosphate group, breaking the bond.

3. Product Formation:

   • The hydrolysis of nucleic acids results in the formation of nucleotide monomers.

   • For example, the hydrolysis of DNA yields deoxyribonucleotides, while the hydrolysis of RNA yields ribonucleotides.

Define monosaccharide.  

• a monosaccharide is the simplest form of a carbohydrate, consisting of a single sugar unit that cannot be broken down to anything simpler

Outline the properties of glucose in terms of solubility​

• Glucose is a polar molecule

• This is because it contains polar functional groups -OH groups

• Oxygen atom present in the ring has a partial negative charge, so the (C-H) group has partial positive charge

• This means glucose can dissolve in water by forming hydrogen bonds with water in blood plasma

Outline the properties of glucose in terms of transportability​

• Because glucose is polar and can dissolve in water, it can also be transported via the bloodstream

• This is essential because it allows cells to receive glucose for cellular respiration

Outline the properties of glucose in terms of stability​

• glucose is cyclic

• the -OH groups situated in the axial regions of the molecule

• Cyclic molecules are more energetically favoured

• This stability allows glucose to perform many roles (cellulose, storage)

Outline the properties of glucose in terms of energy yield from oxidation.

• the ability of glucose to oxidise allows for respiration to occur

• glucose a six carbon molecule is broken down by losing electrons to carbon dioxide and energy is used to generate ATP

• Glucose has many high energy electrons (between C–C and C–H bonds) which can be released via oxidation

• Glucose can by oxidised to produce a large yield of ATP via aerobic cell respiration

Define polysaccharide.  

• Polysaccharides are carbohydrate polymers comprised of many (hundreds to thousands) monosaccharide monomers

Compare the structure and function of amylose, amylopectin, and glycogen.

Amylose :

• linear polysaccharide

• made of alpha-1,4-glycosidic bonds

• a coiled structure

Amylopectin :

• highly branched polysaccharide

• alpha 1,4-glycosidic bonds and alpha 1,6-glycosidic bonds

• allows it to form more complex three dimensional structure → more efficient storage of glucose

• amylopectin is 80-85% of starch

→ starch is the main energy storage molecules in plants because of its coiling and branching allowing it to be compact in structure and stored in specialised plant structures like seeds

Glycogen :

• primary storage form of glucose in animals

• made of alpha glucose

• glycogen is a branched polymer of glucose molecules that form highly compact coiled structures

• glucose chains linked together through alpha 1.4-glycosidic bonds forming the backbone and 1,6-glycosidic bonds that occur every 8-12 glucose units

Discuss the benefit of polysaccharide coiling and branching during polymerization.

• Allows it to form highly compact structures, making it more efficient of an energy store.

Explain how condensation or hydrolysis of alpha-glucose monomers build or mobilize energy stores.​

• When energy is needed, glycogen can be quickly mobilised and broken down into glucose molecules by hydrolysis reaction which can then be used by the body for cellular respiration to release energy

Compare the structure of alpha-glucose and beta-glucose. 

• alpha and beta glucose are isomers of glucose

• Alpha glucose has its hydroxyl group oriented below while Beta glucose has its oriented above

Describe the structure of cellulose microfibrils. 

• Cellulose is made of beta-glucose molecules that form staright chains as beta glucose molecules alternate in orientation

• Form unbranched, long chains grouped into bundles called microfibrils

• Microfibrils are crosslinked

• Hydrogen bonds between create strong and stable lattic with tensile strength

Discuss the consequences of the strength of cellulose in the plant cell wall.

• Cell wall made up of cellulose, other polysaccharides, proteins and lipids

• Gives rigid and sturdy structure, maintaining shape and integrity

• Helps withstand force of osmosis and holds its own weight

• Cellulose provides structural support and protection due to its rigidity and tensile strength

State the function and describe the structure of glycoproteins in the cell membrane. 

• Glycoproteins are proteins that have one or more carbohydrates attached to them

• Either attached to specfific amino acid residues within protein or farm branched/linear chains that extend from protein surface

• Components of blood plasma membranes, positioned with attached carbs facing out

• having different glycoproteins on the surface, cells enable other cells to recognize them

• cell-cell recognition is important for organization, allowing foreign cells/infected cells to be identified or destroyed

Compare the structure of the A, B and O glycoproteins on the red blood cell membrane.

• ABO blood system is a consequence of different glycoproteins on the surface of red blood cells

• RBC either have A or B antigens

• Havin A means A blood group, B means B blood group, both means AB and none means O

Discuss the consequences of the presence of A, B and O glycoproteins during blood transfusion.

• If imcompatible blood types mix, the immune system will recognize these cells as foreign and attack them

• RBC clump up and may lead to organ failure

• Ab is universal recipient, O is universal donor

Explain why lipids are hydrophobic.

Lipids are non-polar and therefore only dissolve in non-polar substances

Outline the structure and function of fats, oils, waxes and steroids.

Fats come in two forms

Triglycerides :

• have one glycerol molecule linked to three fatty acids

Phospholipids :

• one glycerol molecule can link two fatty acid molecules and one phosphate group

Steroids :

• steroids are characterized by a four ring structure

• either hormones or influence membrane fluidity

  Waxes :

• esters made of an alcohol chain and a fatty acid chain

• plants have waxed covered leaves to prevent water loss

Explain the condensation reaction connecting fatty acids and glycerol to form a triglyceride.

• tryglycerides form three water molecules because three fatty acids link to one glycerol

• they are linked by ester bonds

Explain the  condensation reaction connecting fatty acids, glycerol and a phosphate group to form a phospholipid. 

• phospholipids also make three water molecules

• instead of three, two fatty acid molecules and a phosphate group link to one glycerol to form a amphipathic structure

Describe the structure of a generalized fatty acid.

• Generally, there are long linear chains of carbon and hydrogen atoms make up the backbone of a fatty acid molecule

Compare and contrast the structures and properties of saturated and unsaturated (mono- or poly-) fatty acids.

saturated :

• have straight linear shape because here are no double bonds

• each carbon bound to four atoms (usually hydrogen or an adjacent carbon)

• allows them to pack tightly together, forming a solid at room temperature

unsaturated :

• have one or more double bonds which make kinks in the structure

• prevent molecules from packing tightly together

• resulting in a liquid at room temperature

Distinguish between the structure and properties of cis- and trans-unsaturated fatty acids.

cis :

• hydrogen atoms attached to the carbon atom around the double bond are located one the same side of the molecule

• causes kinks, leading to a less linear structure

• occur naturally

trans :

• hydrogen atoms attached to the carbon atoms around the double bond are located on opposite sides of the molecules

• more linear, less flexible and more rigid

• made industrially

Outline properties of triglycerides that make them suitable for long-term energy storage. 

• chemically stable, so energy is not lost over time

• immiscible with water, naturally form droplets in the cytoplasm which do not osmic or else effects

• they release twice as much energy per gram as carbs

• poor conductors of heat, used as insulators

• liquid at room temperature, act as shock absorber

State the function of adipose tissue.

in animals, adipose tissues are where triglycerides are stored. help store energy and thermally insulate the body

Discuss the adaptation of a thick adipose tissue layer as a thermal insulator. 

The bowhead whale as well as others have blubber which is mainly composed of adipose tissues containing large amounts of triglycerides. it keeps the whales warm and acts as energy reserve too

Outline the amphipathic properties of a  phospholipid.

• consists of a negatively charged phosphate head that is also hydrophilic

• hydrocarbon tails consist of non-polar fatty acid chains that are hydrophobic

• this allows them to be amphipathic

Explain why phospholipids form bilayers in water, with reference to hydrophilic phosphate heads and two hydrophobic hydrocarbon tails.

• because phospholipids are amphipathic, when placed in an aqueous environment, the hydrophilic heads face the aquoues environment while the hydrophobic tails arient themselves towards each other

• phosholipids form bilayer spantenously in water

State why steroid hormones are able to pass directly through the phospholipid bilayer.

• as steroids are hydrophobic molecules, they are capable of passing through the phospholipid bilayer of cells, allowing cells to have a faster response to the presence of steroids - more efficient signal?

Outline the differences between steroids and waxes

Steroids:

1. Chemical Structure:

   • Steroids are a type of lipid characterized by a complex four-ring structure, consisting of three cyclohexane rings and one cyclopentane ring fused together.

   • The four rings are arranged in a specific configuration, giving steroids their characteristic shape.

2. Functional Groups:

   • Steroids typically have various functional groups attached to the carbon skeleton, such as hydroxyl (-OH) groups and carbonyl (C=O) groups.

   • Examples of steroids include cholesterol, testosterone, estrogen, and cortisol.

3. Biological Functions:

   • Steroids serve diverse physiological functions in organisms, including:

     • Regulation of metabolic processes (e.g., cholesterol is a precursor for the synthesis of steroid hormones).

     • Maintenance of membrane fluidity and stability.

     • Regulation of gene expression (e.g., steroid hormones act as signaling molecules).

4. Examples:

   • Cholesterol: Found in cell membranes, serves as a precursor for steroid hormones and bile acids.

   • Testosterone: Male sex hormone involved in the development of secondary sexual characteristics.

   • Estrogen: Female sex hormone involved in the regulation of the menstrual cycle and development of secondary sexual characteristics.

   • Cortisol: Steroid hormone involved in stress response and regulation of metabolism.

Waxes:

1. Chemical Structure:

   • Waxes are esters formed from a long-chain fatty acid and a long-chain alcohol (often a fatty alcohol).

   • The fatty acid typically contains 14-36 carbon atoms, while the alcohol portion contains 16-30 carbon atoms.

2. Functional Groups:

   • Waxes contain ester functional groups (-COO-) formed by the condensation reaction between the carboxyl group (-COOH) of the fatty acid and the hydroxyl group (-OH) of the alcohol.

3. Physical Properties:

   • Waxes are typically solid at room temperature but may become liquid at higher temperatures.

   • They are often water-repellent and have protective properties, making them suitable for coating surfaces to prevent water loss and protect against environmental factors.

4. Biological Functions:

   • Waxes serve various biological functions in organisms, including:

     • Water conservation: Waxes form protective coatings on the surfaces of leaves, fruits, and insect exoskeletons, reducing water loss.

     • Protection against pathogens: Waxes create barriers that prevent the entry of pathogens into plant tissues.

     • Protection against environmental stress: Waxes help plants and animals withstand extreme temperatures and UV radiation.

5. Examples:

   • Plant Cuticle: A waxy layer covering the epidermis of leaves and stems, reducing water loss and providing protection.

   • Beeswax: Produced by honeybees, used for constructing honeycomb cells and sealing the hive.

   • Carnauba Wax: Obtained from the leaves of the carnauba palm, used in various products such as cosmetics, polishes, and coatings.