Chapter 3 Biological Molecules Flashcards
What are the 4 key elements? (2 extra)
C (carbon)
H (hydrogen)
O (oxygen)
N (nitrogen)
++ phosphorus (P) and sulphur (S)
What are the KEY biological molecules?
CARBOHYDRATES (carbon, hydrogen, oxygen) - Cx(H2O)x usually
LIPIDS (carbon, hydrogen, oxygen)
PROTEINS (carbon, hydrogen oxygen, nitrogen, and sulfur)
NUCLEIC ACIDS (carbon, hydrogen, oxygen, nitrogen, phosphorus)
Why is water polar?
Covalent bond between O and H (electrons are NOT shared equally)
- oxygen is delta negative
- hydrogen is delta positive
Water = POLAR MOLECULE
Therefore water molecules interact with each other as the positive and negative regions of the molecule attract one another and form HYDROGEN BONDS.
What are the main characteristics of water?
Unusually HIGH boiling point
LESS dense in SOLID state (hydrogen bonds fix the positions of the molecules further apart = tetrahedral arrangement)
COHESIVE properties (molecules attracted to one another)
- moves as one mass
- capillary action
ADHESIVE properties (molecules attracted to other materials)
- capillary action
SURFACE TENSION (water more cohesive to itself than to air)
Acts as a SOLVENT
- as it is polar
Buffers temp. changes (coolant)
STABLE (does not change temp. easily)
What is a monomer of carbohydrate called? Examples?
MONOsaccharide = single sugar unit
- glucose (alpha and beta)
- fructose
- ribose
2 monosaccharides =?? Examples?
DIsaccharide
- lactose (glucose + galactose)
- sucrose (glucose and fructose)
- maltose (alpha and alpha condensation reaction)
Polymer of monosaccharides? Examples?
POLYsaccharide
- glycogen
- cellulose
- starch
Describe the structure of glucose?
C6H12O6
6 carbons = HEXOSE monosaccharide
- alpha
- beta
(in which the OH (hydroxyl) group on carbon 1 is in oppo positions)
Glucose molecules are POLAR and SOLUBLE in water due to the hydrogen bonds which form between the OH (hydroxyl) groups and water molecules.
- means that glucose is dissolved in the cytosol of the cell
Condensation reactions of glucose? (1)
When 2 ALPHA glucose molecules are side by side, 2 OH groups interact.
Water (H2O) is formed as a product.
Bond forms between carbon 1 and 4 = (covalent) GLYCOSIDIC BOND
- alpha + alpha —> maltose (disaccharide)
= condensation reaction, since water is formed as a product
What is sucrose made up of?
FRUCTOSE + GLUCOSE
What is lactose made up of?
GLUCOSE + GALACTOSE
What are pentose monosaccharides?
Sugars that contain 5 carbon atoms (ribose and deoxyribose)
- ribose present in RNA nucleotides
- deoxyribose present in DNA nucleotides
Explain delta charges?
Negative electrons are not always shared equally (in covalent bonds) by the atoms of different elements.
- the atom with the greater share of negative electrons will be delta (slightly) negative
Vice versa
E.g. O—H (hydroxyl group) = polar
What is STARCH?
Glucose made by photosynthesis in plant cells is stored as starch.
‘= a chemical energy store’
What are the two polysaccharides known collectively as STARCH?
AMYLOSE and AMYLOPECTIN
How is AMYLOSE formed?
Formed by alpha glucose molecules joined together ONLY by 1,4 glycosidic bonds.
- the angle of the BOND means that the long chain of glucose TWISTS to form a helix (shape)
- which is further stabilised by hydrogen bonding within the molecule
- making the polysaccharide (amylose) MORE COMPACT and LESS SOLUBLE
(Than the glucose molecules used to make it)
How is AMYLOPECTIN formed?
Also made by 1,4 glycosidic bonds between alpha glucose molecules.
But unlike in amylose…
- there are also some glycosidic bonds formed by condensation reactions between carbon 1 and carbon 6.
= BRANCHED structure
1-6 branching points occurring approximately once every 25 glucose subunits.
What is the equivalent energy storage molecule to starch in ANIMALS and fungi?
GLYCOGEN
Compare glycogen to amylopectin.
Glycogen forms more branches than amylopectin.
= MORE compact
= LESS space needed to be stored
Benefits of the branching?
Animals are mobile, unlike plants.
The COILING and BRANCHING of polysaccharides make them compact, which is ideal for storage.
Also means that there are many FREE ENDS where glucose molecules can be added or removed.
- speeds up processes of storing or releasing glucose molecules required by the cell.
Key properties of amylopectin and glycogen?
- (What makes them ideal for storage roles)??
INSOLUBLE
BRANCHED
COMPACT
How is glucose released for respiration (in animals)?
Starch (glycogen) undergoes HYDROLYSIS reactions.
- requiring the ADDITION of water molecules
Reaction can be catalysed by enzymes.
REVERSE of condensation reactions that form the glycosidic bonds initially.
Why are beta glucose molecules unable to join together in the same way as alpha molecules can?
The hydroxyl (OH) groups on carbon 1 and carbon 4 of two beta glucose molecules are TOO FAR from each other to react.
- the only way that beta glucose molecules can join together and form a polymer is if alternate beta glucose molecules are TURNED UPSIDE DOWN.
Cellulose??
When a polysaccharide is formed from beta glucose (in this alternating way) it is UNABLE to coil or form branches.
A STRAIGHT CHAIN MOLECULE = cellulose
What does cellulose do (cell walls)??
Cellulose molecules make HYDROGEN BONDS with each other forming MICROFIBRILS.
MICROFIBRILS join together forming MACROFIBRILS.
MACROFIBRILS combine to produce fibres.
- these fibres are strong and insoluble
- used to make CELL WALLS
What are REDUCING SUGARS?
Reduction is the GAIN of electrons.
Reducing sugars can donate electrons, or REDUCE another molecule or chemical.
ALL MONOsaccharides and some DIsaccharides (maltose and lactose) are REDUCING sugars.
How do you test for REDUCING SUGARS?
BENEDICT’S TEST using Benedict’s reagent
= an alkaline solution of COPPER (II) SULFATE
(1) Place the sample to be tested in a boiling tube.
(2) Add an equal volume of Benedict’s reagent.
(3) Heat the mixture gently in a boiling water bath for 5 minutes.
How does the Benedict’s test for reducing sugars work?
Reducing sugars will react with the copper ions in Benedict’s reagent.
- the addition of electrons to the Cu 2+ (blue) ions —> Cu + (brick red) ions.
- when a reducing sugar is mixed with Benedict’s reagent and warmed, a brick red precipitate is formed.
- the more reducing sugar present the more precipitate is formed and less Cu 2+ (blue) ions are left in solution.
What TYPE of test is Benedict’s test for reducing sugars?
QUALITATIVE
What will happen if you use Benedict’s test on non-reducing sugars?
Non-reducing sugars do NOT react with Benedict’s solution and the solution remains blue (after heating).
= NEGATIVE result
Most COMMON non-reducing sugar = sucrose.
How do you get a positive result from sucrose (non-reducing sugar) with Benedict’s test?
If sucrose if first BOILED with DILUTE HCl (hydrochloric acid), it will then give a positive result when warmed with Benedict’s solution.
- the sucrose has been HYDROLYSED —> glucose and fructose (reducing sugars)
How do you test for STARCH?
IODINE TEST
(1) A few drops of IODINE dissolved in POTASSIUM IODIDE solution are mixed with the sample.
(2) If the solution changes colour from yellow/brown —> purple/black STARCH IS PRESENT = positive result
Negative result of an iodine test for starch??
The iodine solution remains yellow/brown.
What do you test for with REAGENT STRIPS?
Can new used to test for the presence of REDUCING SUGARS (most commonly glucose).
What is the advantage of reagent strips?
With the use of a colour-coded chart, the concentration of the sugar can be determined.
Explain how COLORIMETRY works?
What elements do lipids contain?
Carbon, Hydrogen, and Oxygen
What are lipids?
NON-POLAR molecules
- as the electrons in the outer orbitals that form the bonds are more evenly distributed than in polar molecules.
- NO REGIONS of negativity and positivity and therefore lipids are INSOLUBLE in water.
(oil and water do not mix)
MACROMOLECULES = built from repeating units (monomers)
What is a triglyceride made up of?
1 GLYCEROL molecule and 3 FATTY ACIDS
- glycerol = a member of the alcohol group
- fatty acids belong to carboxylic acids
(consist of carboxyl group -COOH ++ a hydrocarbon chain)
How are triglycerides formed?
Both glycerol and fatty acid molecules contain a hydroxyl (OH) group.
These groups interact forming…
- 3 H2O molecules (condensation reaction - water removed)
- ESTER BONDS
REACTION = ESTERIFICATION (ester bonds are formed)
- esterification is an example of a condensation reaction
What is an ESTER bond?
— O —C == O
How do you break down a triglyceride?
Since the formation of a triglyceride is a condensation reaction (since 3 H2O molecules are removed)…
3 H2O molecules must be SUPPLIED to reverse this reaction.
= HYDROLYSIS reaction
Saturated??
Fatty acid chains that have NO DOUBLE BONDS present between the carbon atoms…
- since all the carbon atoms form the maximum number of bonds with hydrogen atoms.
Unsaturated??
A fatty acid WITH DOUBLE BONDS between some of the carbon atoms .
(1 double bond = MONOunsaturated)
(2 double bonds = POLYunsaturated)
Unsaturated??
(What does the presence of double bonds do to molecules?)
It causes the molecule to KINK or BEND.
Therefore they CANNOT pack so closely together.
= THEY ARE LIQUID AT ROOM TEMP. rather than solid.
(described as oils rather than fats).
Saturated/Unsaturated at ROOM TEMP. ?
Saturated = no kinks/bends = pack tightly = SOLID (fats)
(inconclusive evidence that it leads to heart disease)
Unsaturated - kinks/bends = can’t pack tight = LIQUID (oils)
(tend to be healthier in a human diet)
What are PHOSPHOLIPIDS?
Modified triglycerides… contain PHOSPHORUS as well as C, H, O.
Inorganic phosphate ions are found in every cell’s cytoplasm.
- contain extra electrons = negatively charged (SOLUBLE)
One of the fatty acid chains of a triglyceride molecule is REPLACED with a PHOSPHATE group = phospholipid.
Structure of phospholipid (DRAW).
-
Structure of triglyceride (DRAW).
-
Describe the structure of a phospholipid?
Non-polar (hydrophobic) TAILS = fatty acid chains
Charged/Polar (hydrophilic) HEAD = phosphate group
Due to their dual hydrophobic/hydrophilic structure, what are phospholipids also called?
SURFACTANTS (surface active agents)
What do phospholipids play a KEY role in?
The formation of CELL MEMBRANES as they can form structures such as, bilayer.
Can SEPARATE the aqueous environment in which cells usually exist from the aqueous cytosol within cells.
What are sterols?
Steroid alcohols.
- they are complex alcohol molecules, based on a 4 carbon ring structure with a hydroxyl (OH) group at one end.
NOT fats or oils.
= dual hydrophilic/hydrophobic
What is cholesterol?
a STEROL
- the body manufactures cholesterol in liver/ intestines.
Important role in cell membranes (positioned between phospholipids (with the OH group being at the periphery of membranes).
= adds STABILITY and regulates FLUIDITY
(By keeping membranes fluid at low temperatures and stopping them becoming too fluid at high temperatures.)
BIOLOGICAL roles of lipids (4)?
(1) membrane formation and (creation of) hydrophobic barriers
(2) hormone production
(3) electrical insulation (for impulse transmission)
(4) waterproofing
STORAGE roles of lipids (3)?
(1) thermal insulation to reduce heat loss
(2) cushioning to protect vital organs
(3) buoyancy for aquatic animals
How can you identify LIPIDS?
EMULSION test
(1) sample is mixed with ethanol
(2) mix solution with water and shake
(3) WHITE EMULSION appears indicating presence of a lipid
- (negative result if solution = remains clear)
What are PEPTIDES?
Polymers made up of amino acid molecules (monomers.)
What do PROTEINS consist of?
Proteins consist of one or more POLYpeptides arranged as complex macromolecules and they have specific biological functions.
- contain elements: C, H, O, and N
Describe the structure of amino acids.
Amino acids have the same basic structure.
Different R-GROUPS (variable groups) result in different amino acids.
Synthesis of peptides??
Amino acids join when the AMINE and CARBOXYLIC groups connected to the central carbon atoms react.
(R groups aren’t involved at this point.)
The HYDROXYL in the carboxylic acid group of one amino acid reacts with a HYDROGEN in the amine group of another amino acid.
= PEPTIDE BOND (condensation reaction - water formed)
How is a PEPTIDE bond formed?
The OH (hydroxyl) group in the carboxylic acid of one amino acid reacts with the H (hydrogen) in the amine of another amino acid.
What type of reaction is the synthesis of peptides?
CONDENSATION reaction (since water is produced)
How is a POLYpeptide formed?
ENZYME catalysed by??
When many amino acids are joined in together by peptide bonds.
This reaction is catalysed by the enzyme, PEPTIDYL TRANSFERASE (present in ribosomes.)
- ribosomes = site of protein synthesis
R group interactions??
The different R groups of the amino acids making up a protein are able to interact with each other forming different types of bonds.
= R GROUP INTERACTIONS
LEADING… to the long chains of amino acids (polypeptides) fading into complex structures (proteins).
- the presence of different sequences of amino acids leads to different structures with different shapes being produced.
SHAPES of proteins (importance)?
The very specific shapes of proteins are vital for the many functions proteins have within living organisms.
What are the different levels of protein structure (brief)?
(1) primary structure
- sequence of amino acids
- affects how polypeptide folds = final shape
- only peptide bonds involved
(2) secondary structure
- O, H, N atoms react (not R groups)
- hydrogens bonds form within aa. chain = coil = alpha helix
- hydrogen bonding causes polypeptide chains to lie parallel to one another = pleated = beta pleated sheet
(3) tertiary structure
- folding of protein into final shape
- secondary structure brings the R groups close enough to interact
- hydrophobic hydrophilic interactions (between polar and non-polar R groups)
- hydrogen bonds
- ionic bonds (between oppositely charges R groups)
- disulfide bonds (bridges) = covalent (between R groups containing sulphur atoms)
(4) quaternary structure
- association of 2 or more proteins (subunits)
- interactions (bonds) are the same as tertiary structure just between separate proteins molecules (not within the same chain)
Hydrophilic/ hydrophobic interactions within protein structure?
Proteins are assembled in the aqueous environment of the cytoplasm.
The way the protein folds will also depend on whether the R groups are phobic or philic.
- phlic on the OUTSIDE
- phobic on the INSIDE
(helps protein shield from the water in the cytoplasm).
Breakdown of PEPTIDES?
PROTEASE are enzymes which catalyse the reverse reaction.
(turn peptides back into amino acids).
= HYDROLYSIS reactions (water is added)
REFORMING the AMINE and CARBOXYLIC ACID groups.
What are GLOBULAR proteins?
- compact
- water soluble (see below)
- roughly spherical in shape
Form when the proteins fold in a way that the phobic R groups are kept away from the aqueous environment and philic R groups are on the outside of the protein.
- tertiary structure
SOLUBILITY of globular proteins is important…
- globular proteins are essential for regulating many vital life processes
INSULIN??
Is a GLOBULAR protein.
- hormone involved in the regulation of blood glucose concentration
