Biological Molecules

Describe covalent bonding.

Atoms share a pair of electrons in their outer shells. As a result the outer shell of both atoms is filled and a more stable compound is formed.

What is the test for starch?

Iodine black

Describe ionic bonding

Ions with opposite charges attract each other. This electrostatic attraction is known as an ionic bond. Ionic bonds are weaker than covalent bods.

Describe hydrogen bonding.

Electrons within a molecule tend to spend more time at one position. This region is more negatively charged than the rest of the molecule. This makes it polarised. The negative region of one polar molecule is attracted to the positive region of another, forming a weak electrostatic bond. Although individual bonds are weak, they can collectively form important forces that alter the physical properties of molecules, like in water.

What are monomers?

The smaller units from which larger molecules are made.

What are polymers?

Molecules made from lots of repeating units (monomers) joined together.

What is a condensation reaction?

A condensation reaction joins two molecules together with the formation of a covalent bond and involves the elimination of a water molecule.

What is a hydrolysis reaction?

Breaks the covalent bond between two molecules and involves the use of a water molecule.

What 3 elements make up all molecules of life?

Carbon, hydrogen, oxygen

What is metabolism?

All the chemical processes that take place in living organisms.

What are amino acids?

The monomer that makes up proteins. has a central carbon atom which is bonded to: a carboxylic acid group, an amino group, a hydrogen atom and a R group.

What are monosaccharides?

A single sugar e.g. glucose. The monomers of long chain carbohydrate polymers.

What are nucleotides?

A compound consisting of an organic base and ribose sugar linked to a phosphate group. Nucleotides form monomers of nucleic acids such as DNA.

What are polysaccharides?

Polymers of monosaccharides. Glycosidic bonds form between the monosaccharides. Examples are glycogen, cellulose and starch. Respiratory substrates and structure.

What are polynucleotides?

Monomers are nucleotides. Bonded with phosphodiester bonds. Examples are DNA and RNA.

What is an isomer?

compounds with the same formula but a different arrangement and, therefore, different properties.

Properties of monosaccharides

Sweet, soluble, reducing

What is maltose?

A disaccharide formed of glucose + glucose

What is lactose?

Glucose + galactose

What is sucrose?

glucose + fructose

Properties disaccharides

sweeter, soluble, may be reducing

Starch properties

Formed of alpha glucose monomers. mixture or amylose and amylopectin. Used by plants to store glucose as it is insoluble and too large tonleave cells.

What is amylose?

Coils to store more energy densely

What is amylopectin?

Has branches which increase surface area increasing enzyme activity allowing glucose to be released quickly. 1-4 straight thing 1-6 branches

What is glycogen?

Alpha glucose. Long, branched 1-4 and 1-6. Branches increase surface area for enzymes meaning glucose can be released quickly. It is also a compact molecule so stores densely. Used to store excessive glucose in liver and muscle cells.

What is cellulose?

Beta glucose. Long straight chains with 1-4 bonds. Right way up upside down right way up. chains linked by hydrogen bonds. Very strong, flexible. Provide support and turgidity. Used in cell walls.

What is a reducing sugar?

A sugar that serves as a reducing agent.

Hexose sugar

A sugar made up of 6 carbons

Describe benedicts test for reducing sugars

Add 2cm³ sample Add benedicts Heat at 90⁰c for 5 minutes Semi-quantitative result from green to brick red

Why is positive result brick red?

Copper oxide is formed from copper sulfate in the benedicts reagent

What is the test for non-reducing sugars?

Normal benedicts tes tAdd 2cm³ sample Heat with dilute hydrochloric acid at 90⁰c for 5 minutesNeutralise with sodium hydroxideBenedicts test

What are the two main lipids?

Triglycerides and Phospholipids

What are triglycerides

Formed by a condensation reaction between one molecule of glycerol and three molecules of fatty acid.

What two groups do the condensation reactions occur between to form ester bonds?

Hydroxyl groups of glycerol and the carboxyl group of the fatty acids.

What is the R group in fatty acids?

The variable hydrocarbon group, attached to a carboxyl group.

Saturated vs unsaturated fatty acids

Saturated: Contain no C=C double bonds. Unsaturated: Contain at least one C=C double bond.

How do the double bonds affect the properties of fatty acids?

Saturated fatty acids are usually solid at room temp as their straight shape allows them to pack closely together. Unsaturated fatty acids are usually liquid at room temp as their kinks mean they cannot pack tightly together, lowering their melting point.

What are phospholipids

Glyceride, two fatty acids and a phosphate group. They are polar and the phosphate head is hydrophilic, while the fatty acid tail is hydrophobic. Two ester bonds and one phosphoester bond.

What is a phospholipid bilayer?

Phospholipids spontaneously self-assemble to a bilayer in aqueous environments. Heads point outward toward the cytoplasm and extracellular fluid. Tails sandwich together on the inside, blocking water-soluble substances.

How does the structure of a triglyceride aid its function

The high ratio of energy storing C-H bonds to carbon atoms = efficient energy storage. Large non-polar and insoluble means they do not alter the water potential of the cell. High ratio of hydrogen to oxygen atoms: release metabolic water when oxidised.

How does the structure of a phospholipid aid its function?

Form bilayer as in an aqueous environment, hydrophilic heads face outward toward water, while hydrophobic tails point inward away from water. Kinks in unsaturated fatty acid tails prevent packed rigidity increasing fluidity and flexibility Combine with carbohydrates at the cell-surface membrane to create glycolipids, which are crucial for cell recognition

Describe the emulsion test for lipids.

1. Add ethanol to the test sample 2. Shake thoroughly to dissolve any lipid present 3. Add distilled water to the mixture and shake gently. 4. A cloudy white emulsion should form

Describe the structure of an amino acid.

Central carbon atom bonded to four distinct groups. 1. Amine group (-NH 2 ) basic 2. Carboxyl Group (-COOH) acidic group 3. Hydrogen atom (-H) 4. Variable side chain (-R group) determines the chemical properties and identity of the specific amino acid. R | H2N--C--COOH | H

How many amino acids are there?

20 (9 essential)

What are dipeptides?

Formed by the condensation of two amino acids (peptide bond)

What are polypeptides?

Formed by the condensation of more than two amino acids.

Which molecules react to form peptide bonds?

A hydroxyl group from the carboxyl group and the hydrogen from the amine group

Proteins are amphoteric. Why? What does it mean?

They can act as an acid or base (can be buffer) due to having a basic amine group and an acidic carboxyl group.

Essential amino acids vs non-essential amino acids

Essential - must get from diet (9) Non-essential - body can synthesize them.

What is primary structure of proteins

Determined by sequence of amino acids, which can affect shape and function

What is the secondary structure of proteins?

Determined by the hydrogen bonds. which cause it to fold into a β-pleated sheet or coil into a α helix

What is the tertiary structure of proteins?

The 3D shape, determined by sequence, hydrogen bonds, ionic bonds and disulphide bridges (covalent bonds)

What is the quaternary structure of proteins?

If proteins are made of more than one polypeptide chain.

What is the biuret test? Describe the method

A qualitative test designed to verify the presence of peptide bonds within a solution. 1. Add biuret reagent (NaOH and Cu(II)SO 4 . 2. Positive: blue to purple Test detects peptide bonds and will yield a negative result for free individual amino acids.

What is chromatography of amino acids? Describe the method

Used to isolate, separate, and identify components within an unknown mixture of amino acids, because different amino acids have a different Rf value. 1. Spot the sample onto a chromotography paper baseline and place it into a suitable solvent. The solvent migrates up the paper via capillary action. 2. Visualisation: amino acids are colourless. The chromatogram must be sprayed with ninhydrin reagent and heated to turn the amino acid spots purple. 3. Identification: the Rf value can be matched with the known Rf value of amino acids to work out which are present