Biological molecules

Importance of water having a High latent heat of vaporisation

Sweating acts as a cooling mechanism as high energy water molecules evaporate leaving the cooler water molecules behind

Importance of water having a high specific heat capacity

Hydrogen bonds absorb high amounts of energy preventing rapids swings in temperature in cells and aquatic habitats to prevent enzymes denaturing

Density of water as a solid (ice)

Ice less dense so floats and insulates water below ice allowing organisms to survive

Importance of Cohesion and surface tension in water molecules

Cohesion : Polar water molecules attracted to each other due to hydrogen bonds so a water column is created - pull water up xylem in plants

Surface Tension : Inward pulling forces at air-water interfaces creating a layer, skin like tension

Importances of water

• High Specific Heat Capacity

• High Latent Heat Of Vaporisation

• Density as a solid

• Dilutes Toxic substances - e.g urea

• Transport Medium - e.g sugars and amino acids in phloem or creating cohesive columns to pull up minerals

• Good Solvent

What bonds hold two monosaccharides to produce a disaccharide in a condensation reaction

Glycosidic bonds

Name examples of disaccharides and molecule breakdown

Maltose - 1 Glucose + 1 Glucose

Sucrose - 1 Glucose + 1 Fructose

Lactose - 1 Glucose + 1 Galactose

What are Monosaccarides?

Monomers of more complex carbohydrates

Properties of Monosaccarides

Soluble in water

Form Crystals

How is water a good transport medium/good solvent?

Polarity allows to dissolve many substances: Blood plasma carrying glucose and urea or Phloem dissolving sugars to be transported in plants

Water Polarity

Electrons not equally distributed through bonds due to oxygen being more electronegative so the oxygen atom is slightly more negative and the two hydrogen atoms slightly more positive

Glycogen

-Polysaccharide

-Main form of energy for animals

-Made up of lots of alpha glucose molecules

-Lots of side branches allowing rapid energy release.

- Molecule is large but compact to maximise energy storage

Examples of polysaccharides

Glycogen

Starch

Cellulose

Starch

Stores energy in plants

Mix of two polysaccharides - amylose and amylopectin

Starch can be quickly converted to glucose for respiration

Amylose

Component of Starch

Polysaccharide

Unbranched chain of glucose molecules with 1,4 glycosidic bonds

Compact and can coil up to maximise energy storage

Amylopectin

Component of starch

Polysaccharide

Has many side branches with 1,4 glycosidic bonds

Branches have 1,6 glycosidic bonds so glucose can be released at a faster rate

Cellulose

Constructed of many beta glucose molecules

Every other beta molecule flipped 180 degrees so OH groups match and a 1,4 glycosidic bond is formed

Component of cell walls in plant cells

What are the main uses of lipids in living organisms?

Lipids are used as an energy source, energy stores, membrane components, insulation, protection, and hormones.

How are lipids used as an energy source?

Lipids are broken down during respiration to release energy and generate ATP.

Where is lipid energy stored in animals?

Lipid energy is stored in adipose tissue.

How are lipids used in cell membranes?

Lipids, particularly phospholipids, form the basic structure of cell membranes.

How do lipids provide protection?

Lipid stores and adipose tissue can protect organs from physical damage.

What type of hormones are made from lipids?

Some hormones are lipid-based steroid hormones, such as testosterone.

Which elements are found in lipids?

Lipids contain carbon, hydrogen, and oxygen.

Why are fats energy-rich molecules?

Fats contain many carbon-carbon and carbon-hydrogen bonds, which store a large amount of chemical energy.

What does it mean if a molecule is non-polar?

It means that electrons are distributed relatively evenly, so the molecule has no significant partial charges.

Why are lipids non-polar?

Lipids are non-polar because their electrons are distributed relatively evenly.

Are lipids soluble in water?

No. Lipids are insoluble in water.

Why are lipids insoluble in water?

Lipids do not form hydrogen bonds with water because they are non-polar.

Why are lipids effective energy-storage molecules?

Lipids are insoluble in water, so they do not affect the water potential of cells.

What does the prefix in a lipid name indicate?

The prefix indicates the number of fatty acids in the lipid.

How many fatty acids are present in a triglyceride?

A triglyceride contains three fatty acids.

What type of bond joins components in a lipid?

An ester bond joins the components of a lipid.

What is a triglyceride made from?

A triglyceride is made from one glycerol molecule and three fatty acid molecules.

How are triglycerides formed?

Triglycerides are formed when glycerol and three fatty acids join in condensation reactions, forming ester bonds.

What is released during the formation of an ester bond?

Water is released during the condensation reaction that forms an ester bond.

How are triglycerides broken down?

Triglycerides are hydrolysed into glycerol and fatty acids.

What happens to the products of triglyceride hydrolysis during respiration?

Glycerol and fatty acids can be broken down in respiration to produce carbon dioxide, water, and ATP.

What are the products of completely respiring lipids?

Carbon dioxide, water, and ATP are produced.

Why does respiring a lipid release more water than respiring a carbohydrate?

Lipids contain proportionally more hydrogen, which combines with oxygen during respiration to form more water.

What is a monounsaturated fatty acid?

A monounsaturated fatty acid contains one carbon-carbon double bond.

What is a polyunsaturated fatty acid?

A polyunsaturated fatty acid contains more than one carbon-carbon double bond.

What type of fatty acids are commonly found in animal fats?

Animal fats commonly contain saturated fatty acids.

Why are animal fats often hard?

Saturated fatty acid chains are straight and pack closely together, making the fat denser and more likely to be solid.

How do saturated fatty acids affect animal fats?

They make animal fats harder, allowing them to provide effective protection and insulation.

What type of fatty acids are commonly found in plant oils?

Plant oils commonly contain unsaturated fatty acids.

Why are many plant oils liquid at room temperature?

Unsaturated fatty acids contain double bonds that create bends in the chains, preventing them from packing closely together.

How are saturated fatty acid chains shaped?

Saturated fatty acid chains are straight because they contain no carbon-carbon double bonds.

Why do saturated fatty acids pack closely together?

Their straight chains can align closely with one another.

What is a phospholipid?

A phospholipid is a lipid containing glycerol, fatty acid tails, and a phosphate group.

Where are phospholipids found?

Phospholipids are found in the plasma membranes of cells.

What structure do phospholipids form in cell membranes?

Phospholipids form a phospholipid bilayer.

What are the two main parts of a phospholipid?

A phospholipid has hydrophilic phosphate heads and hydrophobic fatty acid tails.

Why is the phosphate group of a phospholipid hydrophilic?

The phosphate group is polar, so it can interact with water.

Why are the fatty acid tails of a phospholipid hydrophobic?

The fatty acid tails are non-polar, so they do not interact with water.

What does hydrophilic mean?

Hydrophilic means water-attracting or able to interact with water.

What does hydrophobic mean?

Hydrophobic means water-repelling or unable to interact readily with water.

How are phospholipids arranged in a bilayer?

The hydrophilic heads face the watery cytoplasm and tissue fluid, while the hydrophobic tails face inwards away from water.

What is the function of the hydrophobic tails in a phospholipid bilayer?

The hydrophobic tails cluster together and help form the interior of the membrane bilayer.

What is the function of the hydrophilic heads in a phospholipid bilayer?

The hydrophilic heads interact with the cytoplasm and the fluid outside the cell.

Why do phospholipids form bilayers in water?

The hydrophilic heads face the water while the hydrophobic tails cluster away from it.

How can cholesterol be recognised in a structural diagram?

Cholesterol has four fused rings and a hydrocarbon chain.

What is the role of cholesterol in biological membranes?

Cholesterol helps stabilise biological membranes.

How does cholesterol stabilise cell membranes?

Cholesterol fits between phospholipids and helps regulate membrane stability and fluidity.

Why can cholesterol fit between phospholipids?

Cholesterol has a relatively flat structure that fits between phospholipid molecules.

What hormones can cholesterol help produce?

Cholesterol is used to produce steroid hormones.

What vitamins can cholesterol help produce?

Cholesterol is involved in the production of vitamin D.

What digestive substance is cholesterol involved in producing?

Cholesterol is involved in the production of bile.

What elements do proteins contain?

Carbon, hydrogen, oxygen, nitrogen and sulphur.

What are the monomers of proteins?

Amino acids.

What are proteins/polypeptides made from?

Many amino acids joined together by peptide bonds.

What bond joins amino acids together?

A peptide bond.

What is a dipeptide?

Two amino acids joined by a peptide bond.

What is a polypeptide?

More than two amino acids joined by peptide bonds.

What groups does every amino acid have?

An amino group, a carboxylic acid group, a hydrogen atom and a variable R group, all attached to a central carbon atom.

What is the R group of an amino acid?

The variable side chain that differs between the 20 amino acids.

How many different amino acids are commonly found in proteins?

20.

What determines the structure and function of a protein?

The number, sequence and order of its amino acids.

What is the primary structure of a protein?

The specific sequence and number of amino acids in a polypeptide chain.

Why does primary structure affect protein function?

The sequence determines where bonds form and how the protein folds, which determines its final 3D shape and function.

What is the secondary structure of a protein?

The first level of coiling or folding of the polypeptide chain, forming an alpha helix or beta pleated sheet.

What holds the secondary structure of a protein together?

Hydrogen bonds.

Where do hydrogen bonds form in protein secondary structure?

Between the C=O group of one peptide bond and the N-H group of another.

What are the two main types of secondary protein structure?

Alpha helix and beta pleated sheet.

What is the tertiary structure of a protein?

The overall 3D shape formed by further folding and coiling of the polypeptide chain.

What bonds hold tertiary structure together?

Hydrogen bonds, ionic bonds, disulfide bonds, and hydrophobic/hydrophilic interactions.

Which bonds in tertiary structure form between R groups?

Hydrogen bonds, ionic bonds and disulfide bonds.

What are disulfide bonds?

Strong covalent bonds formed between the R groups of cysteine amino acids.

Which amino acid forms disulfide bonds?

Cysteine.

Why is keratin strong?

It contains many cysteine amino acids, which form many strong disulfide bonds.

What are ionic bonds in proteins?

Attractions between oppositely charged R groups; their strength can depend on pH.

What are hydrogen bonds in protein tertiary structure?

Weak attractions between slightly positive and slightly negative parts of R groups.

What are hydrophobic interactions in proteins?

Hydrophobic R groups cluster together in the inside of the protein, excluding water.

What are hydrophilic interactions in proteins?

Hydrophilic R groups face outwards towards water, helping soluble proteins stay stable in aqueous environments.

What is a globular protein?

A compact, usually water-soluble protein with a roughly spherical 3D shape, such as an enzyme or haemoglobin.

What is a fibrous protein?

A long, strong, usually insoluble protein that forms fibres, such as collagen, keratin and elastin.

Give an example of a globular protein.

Haemoglobin, insulin or enzymes.

Give examples of fibrous proteins.

Collagen, keratin and elastin.

What is haemoglobin?

A water-soluble globular protein made of two alpha and two beta polypeptide chains, each containing a haem group.