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Biological Molecules Flashcards

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1
Q

Monosaccharide

A

A single sugar molecule.

  • The simplest carbohydrate which only contain carbon , hydrogen and oxygen.
  • Soluble in water ~ have a large number of OH (hydroxyl) groups which can form hydrogen bonds with water molecules.

Examples :
- Glucose
- Galactose
- Fructose

hexose sugar ~ six carbon atoms
pentose sugars ~ five carbon atoms
triose sugars ~ three carbon atoms

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2
Q

ISOMERS and the two forms of glucose

A

Isomer ~ molecules with the same formula , but whose atoms are arranged differently in space.

Glucose ~ C6H12O6

Beta glucose ~ Carbon 1 hydroxyl points ABOVE the ring.

Alpha glucose ~ Carbon 1 hydroxyl points BELOW the ring.

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3
Q

Disaccharides

A

Form when two monosaccharides chemically react together, contain TWO saccharide molecules.

Examples:
Maltose ~ (glucose + glucose)
Sucrose ~ (glucose + fructose)
Lactose ~ ( glucose + galactose)

Maltose:
- Disaccharide of two alpha glucose molecules.

  • forms a GLYCOSIDIC BOND between carbon 1 and carbon 4 .
  • This is because a molecule of water is formed from a hydrogen atom from one of the monosaccharides and a hydroxyl group from another ~ known as a CONDENSATION REACTION.
  • Leaves an oxygen atom acting as a link between the two monosaccharide units
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4
Q

Hydrolysis Reaction

A
  • if we add WATER to a disaccharide we BREAK the glycosidic bond.
  • The disaccharide converts back to original monosaccharide.
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5
Q

Polysaccharide

A
  • Polysaccharides are POLYMERS of monosaccharides.
  • made of hundreds or thousands of monosaccharide monomers bonded together.

HOMOpolysaccharide ~made solely of one kind of monosaccharide.

HETERpolysaccharide ~ made of more than one monomer.

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6
Q

The energy source : GLUCOSE

A
  • Produced in plant cells using light energy trapped during photosynthesis.
  • A store of chemical energy which can be released during respiration.
  • The energy released is used to make ATP , which is the energy currency of the cell.

SOLUBLE IN WATER:

  • contains hydroxyl groups which are polar due to the small negative charge on the oxygen atom and the small positive charge on the hydrogen atom.
  • This means hydroxyl groups can form hydrogen bonds with water molecules.

PROBLEM ~ allows water to move into the cell by osmosis.

SOLUTION ~ plant cells store glucose as STARCH in starch grains.

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7
Q

The energy store : STARCH

A

Consists of TWO types of polysaccharides:
- Amylose
- Amylopectin

Amylose and amylopectin are POLYMERS:
They are too large to diffuse through the cell membrane and pass out of the cell.

Insoluble in water :
Starch does not cause water to enter the cell by osmosis.

ENZYMES:
Used when the cell needs glucose to break the glycosidic bond in starch. Water is used as is known as a hydrolysis reaction.

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8
Q

Amylose

A

A polymer of alpha glucose molecules.

  • If we join together a large number of alpha glucose molecules , we make the polysaccharide amylose.
  • It has glycosidic bonds between 1 and 4.

Spiral / HELIX shape:
This makes starch COMPACT allowing a large amount of glucose molecules to be stored for its size.

HYDROGEN BONDS form between glucose molecules along the chain , hold the helix in place.

HYDROXYL GROUPS situated on carbon 2 are located on the inside of the coil making the molecule LESS soluble in water.

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9
Q

AMYLOPECTIN

A

A polymer of alpha glucose molecules.

BRANCHES:
- every 25-30 glucose molecules.

  • simply another chain of alpha glucose molecules joined by a 1, 4 glycosidic bond.
  • The branch is joined to the main chain by a 1, 6 glycosidic bond
  • Provide a large number of ends to allow ENZYMES to break down starch rapidly.
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10
Q

GLYCOGEN

A
  • In ANIMALS , the glucose storage molecule is glycogen.
  • Major stores are found in liver and muscle cells.
  • A polymer of ALPHA glucose molecules which are joined together by 1,4 glycosidic bonds.
  • Glycogen has BRANCHES which are joined to the main chain by 1,6 glycosidic bonds.

GLYCOGEN OR AMYLOPECTIN?
They have the same structure , but glycogen is MORE BRANCHED making it a very COMPACT molecule.

LARGE NUMBER OF BRANCHES:
- lots of free ends
- ENZYMES can convert glycogen back to glucose very rapidly .
- This is important for animals as:
- HIGH rate of respiration
- ENERGY NEEDS of animals can change very quickly.

INSOLUBLE IN WATER:
Does not allow water into cells by OSMOSIS preventing the cell from bursting.

LARGE MOLECULE:
Glycogen cannot DIFFUSE out of the cell.

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11
Q

CELLULOSE

A
  • A major part of the CELL WALL found in plant cells.
  • Polymer of BETA glucose.
  • Hydroxyl group on carbon 1 pints ABOVE the plane of the ring.
  • Every SECOND beta glucose rotates 180 degrees so a glycosidic bond can form between carbons 1 and 4.

STRAIGHT CHAINS WITH NO BRANCHES:
- Allows cellulose molecules to get close together.
- HYDROGEN BONDS can form between neighbouring chains.
- A huge number of hydrogen bonds form, making cellulose extremely STRONG.

MICROFIBRILS & MACROFIBRILS:
- When 60-70 cellulose chains group together they form MICROFIBRILS.
- These group together to form large structures called MACROFIBRILS.
- These group together to form a CELLULOSE FIBRE which forms the plant cell wall.

STRUCTURE:
- Macrofibrils and microfibrils have a very high TENSILE STRENGTH due to the glycosidic bonds and the hydrogen.
- Macrofibrils CRISS CROSS the wall for extra strength.
- Difficult to DIGEST ~ the glycosidic bonds are less easy to break.

PLANT CELL WALL FUNCTION:
- Strength and support ~ plants do not have a rigid skeleton.
- Permeable ~ SPACES between macrofibrils allow water and mineral ions to pass on their way in and out of the cell.

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12
Q

PROTEINS

A

Large polymers compromised of long chains of AMINO ACIDS.

Functions:
- blood clotting
- enzymes
- transport
- hormones
- motors
- toxins
- lubrication
- antibodies

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13
Q

AMINO ACIDS

A
  • There are TWENTY different amino acids found in biology.
  • Contain the elements carbon, hydrogen, nitrogen , oxygen and sometimes sulfur .

Consist of :
- Amine group NH2
- Carboxyl group COOH
- R group varies with each amino acid

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14
Q

Peptide bond

A
  • When we join two amino acids a HYDROXYL GROUP is lost from one amino acid and a HYDROGEN from the other.
  • This leads to the loss of water known as a CONDENSATION REACTION.
  • When two amino acids join together is is known as a DIPEPTIDE.
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15
Q

Polypeptide & hydrolysis reaction

A
  • When THREE or more amino acids are joined.
  • ONE molecule of water is form for EVERY peptide bond.
  • Polypeptides often consist of HUNDREDS of amino acids joined.

HYDROLYSIS REACTION:
If we add a molecule of water, we REVERSE the reaction and break the polypeptide bond.

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16
Q

Primary structure

A
  • The SPECIFC ORDER of amino acids in a polypeptide.
  • Helps determine the 3D shape of a protein.
  • The SHAPE of a protein is critical for its FUNCTION.
  • Even changing A SINGLE amino acid in the primary structure can change the final shape of the protein.
  • The primary structure is determined by the DNA SEQUENCE of the GENE which encodes that polypeptide.
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17
Q

SECONDARY STRUCTURE

A
  • This is formed due to the HYDROGEN BONDS that form between amino acids all along the polypeptide chain.
  • These bonds cause the polypeptide chain to TWIST and FOLD into shape known as the secondary structure.
  • Hydrogen bonds are form as a result of the small - charge of the oxygen atoms in C=O group and the small + charge of the nitrogen atoms in the N-H group which ATTRACT each other.
  • The type of secondary structure formed , depends on the primary structure in that region. It is either:

Alpha helix ~ helical shaped
Beta pleated sheet~ flat & sheet like
Both of these contain HYDROGEN BONDS that hold the shape in place.

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18
Q

Tertiary structure

A
  • the overall 3D shape of the polypeptide chain.
  • After the chain has folded into regions of secondary structure, the chains now CONTINUE FOLDING , forming the tertiary structure.
  • Critical for how a protein FUNCTIONS.
  • Different bonds form between the amino acids to hold the precise shape in place.
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18
Q

Quaternary structure

A
  • A large number of proteins consist of several polypeptide chains working together as a large molecule, known as SUBUNITS.
  • The quaternary structure shows how the individual subunits are ARRANGED to form a LARGER 3D SHAPE.
    (Quaternary structure only applies to proteins with TWO OR MORE subunits)
  • Some proteins contain other NON-PROTEIN molecules called PROSETHIC GROUPS which help the protein carry out its function.
  • Proteins with a prosethic group are called CONJUGATED PROTEINS.
  • The quaternary structure shows the POSITION of any prosethic groups.
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19
Q

Hydrogen bonding

A
  • Form sue to the slight + and - charges present on the hydroxyl
  • WEAK BONS ~ are easily broken by high temperature and PH changes
20
Q

Hydrophobic & Hydrophilic interactions

A

Hydrophobic:
- NOT attracted to water
- Located in the CENTRE of proteins

Hydrophilic:
- ATTRACTED to water
- Located on the SURFACE of proteins

21
Q

Ionic bonding

A
  • Found between amino acids with OPPOSITELY CHARGE R groups.
  • Broken with PH changes ~ why enzymes denature in acidic and alkaline conditions.
22
Q

Disulfide bonding

A
  • When two atoms form a covalent bond
  • Usually occurs in the sulfur containing amino acid CYSTEINE.
  • STRONG BOND ~ not broken by high temperatures or PH changes.
23
Q

GLOBULAR proteins

A
  • Approximate spherical shape
  • FUNCTIONAL proteins
  • SPECIFIC shape - helps them to take up roles as enzymes, hormones & haemoglobin.
  • More sensitive to changes in heat and PH.

SOLUBLE in water:
-Hydrophilic amino acids are on the outer surface.
- Hydrophobic amino acids are found deep in the centre , well away from any water molecules.
- This means the hydrophilic R group can INTERACT with water molecules.

24
Q

Globular protein : HAEMOGLOBIN

A
  • The quaternary structures is made up of FOUR polypeptide subunits, TWO alpha subunits & TWO beta subunits.
  • Found in RED BLOOD CELLS where it binds reversibly to OXYGEN.
  • Haemoglobin binds to oxygen in the LUNGS and then it releases the oxygen in the BODY TISSUES.
  • Each subunit contains the prosthetic group HAEM.
  • This means haemoglobin is a CONJUGATED protein.
  • Each haem group contains the Fe2+ ion , and this is where OXYGEN BINDS.
  • This means that ONE haemoglobin molecule can bind to FOUR oxygen molecules.
  • When oxygen attaches , the QUATERNARY STRUCTURE slightly changes, making it EASIER for oxygen to attach.
25
Q

Globular protein : INSULIN

A
  • A HORMONE carried in the bloodstream which plays a role in BLOOD GLUCOSE regulation.
  • Consists of TWO polypeptide chains, an alpha and beta, which FOLD into tertiary structure then linked by DISULFIDE BONDS.
  • Hormones carry out their functions by binding to SPECIFIC RECEPTOR molecules.
  • Receptors are PROTEINS found on the CELL MEMBRANE of target cells.
  • The SHAPES of protein hormones are CRITICAL for how they BIND to their receptors and carry out their EFFECTS.
26
Q

Globular proteins : ENZYMES

A
  • Only react with a SPECIFIC SUBSTRATE molecule.
  • This specificity is due to the STRUCTURE of the enzyme.
  • The ACTIVE SITE of an enzyme is perfectly shaped to fit the SUBSTRATE making them extremely SPECFIIC.

LYSOZYME:

  • Found in SALIVA and TEARS.
  • made up of a single polypeptide chain
  • the chain fold to form the active site.
  • the shape of the active site means that it
    fits perfectly to the substrate molecule in
    the BACTERIAL CELL WALL.

Some amino acids HOLD the substrate in place, whilst others CATALYSE the reaction

27
Q

Fibrous proteins

A
  • Have a REGULAR, repetitive sequence of amino acids
  • Play a STRUCTURAL role.
  • Form LONG, ROPE-LIKE molecules

INSOLUBLE in water:
- have a large proportion of amino acids with HYDROPHOBIC R groups

28
Q

Fibrous protein : COLLAGEN

A

FOUND IN:
Tendons ~ connecting muscles to bone
Ligaments ~ connect bones to each other
Artery walls ~ prevents bursting from high pressure of blood.

Provides MECHANICAL STRENGTH due to its STRUCTURE:

  • The polypeptide chains , wrap tightly together to form a TRIPLE HELIX.
  • Every THIRD amino acid is GLYCINE with the SMALLEST R group HYDROGEN , allowing the polypeptides to wrap tightly around each other.
  • HYDROGEN BONDS form between the polypeptide chains , STABILISING the quaternary structure of the protein.
  • STRONG CROSSLINKS join the polypeptide chains.
29
Q

Fibrous protein : KERATIN

A

FOUND IN:
- Hair
- Fingernails
- Outer surface of skin

  • Contains very HIGH proportion of the amino acid CYSTEINE .
  • These are used to form DISULFIDE BONDS which are STRONG COVALENT bonds.
  • This contributes to the STRENGTH of keratin molecules.
  • Provides and IMPERMEABLE BARRIER to infection .
  • WATERPROOF , preventing the entry of water-borne pollutants.
30
Q

Fibrous protein : ELASTIN

A

FOUND IN:
Skin ~ making it supple and elastic

Walls of arteries
lungs
bladder
This is because elastin can STRETCH and RECOIL allowing MOVEMENT or STORAGE.

ELASTIC:
- Elastin molecules molecules are stretched
- The strands move apart but remain
ATTACHED at the crosslinks.
- After stretching , the elastin molecules
REASSOCIATE springing back together.

31
Q

Hydrogen bonding in water

A
  • A molecule of water contains one atom of OXYGEN and two atoms of HYDROGEN.
  • The bonds between them are COVALENT bonds.
  • The oxygen atom has a SMALL NEGATIVE charge and the hydrogen atoms have a SMALL POSITIVE charge.
  • Because of these charges , water is a POLAR MOLECULE.
  • The opposite charges mean that water molecules are ATTRACTED to each other.
  • These forces of attraction are called HYDROGEN BONDS.
  • These are quite WEAK , however, even a SMALL volume of water contains a LARGE NUMBER of hydrogen bonds, so they have a large effect on the properties of water.
32
Q

Property 1 : HIGH SHC

A
  • We have to put in or take out a large amount of energy to change the temperature of water.
  • When we heat water , the heat energy goes towards WEAKENING or BREAKING the hydrogen bonds rather than increasing the kinetic energy of the water molecules.
  • This means the temperature of water tends not to change rapidly.
  • This allows water to act as a HABITAT for AQUATIC organisms.
33
Q

Property 2 : LESS DENSE IN SOLID FORM THAN LIQUID FORM

A
  • This allows ICE to FLOAT on water.
  • This can act as a HABITAT for a number of organisms such as POLAR BEARS.
  • This ice INSULATES the water below and PREVENTS it from freezing.
  • This means organisms can continue to live in the water under the ice.
34
Q

Property 3 : HIGH LATENT HEAT OF VAPOURISATION

A
  • Takes a LARGE amount of heat energy to EVPORATE water.

-This allows organisms to COOL themselves without losing a great deal of water.

  • SWEATING ~ heat energy is used to evaporate water from the surface of the skin and this transfer of heat energy allows organisms to cool down.
35
Q

Property 4 : SOLVENTS

A
  • Lots of substances can dissolve in water.
  • Both EUKARYOTIC and PROKARYOTIC cells contain a large amount of dissolved substances.
    EXAMPLES:
  • Chemicals involved in metabolic reactions such as respiration.
  • Enzymes needed to carry out these reactions.
  • Ponds and rivers contain dissolved OXYGEN and this is used by organisms living in the water to carry out respiration , making water an excellent HABITAT for organisms.

A GOOD TRANSPORT MEDIUM:

Blood plasma ~ contains a large number of dissolved substances such as CO2 and mineral ions.

Xylem vessels of plants ~ mineral ions pass into the plant roots from the soil and transported in the xylem to the leaves.

36
Q

Property 5 : COHESION

A
  • Water molecules tend to STICK together due to the HYDROGEN BONDS between water molecules.
  • Allows LONG COLUMNS of water to travel in the XYLEM TUBES.
  • This makes water an ideal transport medium in plants.
  • Also causes SURFACE TENSION where water meets air.
  • This is useful as it allows the surface of water to act as a HABITAT for organisms such as the insect PONDSKATERS.
37
Q

Property 6 : METABOLIC REACTIONS

A

REACTANT:
- Hydrolysis reactions
- Photosynthesis

PRODUCT:
- Condensation reactions
- Aerobic respiration

38
Q

Lipids & its uses

A
  • Fats and oils

Uses:
- Energy SOURCE e.g in human diet
- Energy STORE e.g Adipose tissue
- Protection e.g delicate organs
- Thermal and electrical INSULATOR
- Waterproofing
- Major part of the structure of membranes
e.g in cells and mitochondria

39
Q

Triglyceride

A
  • A type of LIPID

General formula:
- A molecule of GLYEROL C3H8O3
- Bonded to 3 FATTY ACIDS

NON POLAR :
- Means they are hydrophobic, do not dissolve in water.
- Explains why they are used for WATERPROOFING.

LARGE number of C and H atoms:
- A great deal of energy can be RELEASED from triglycerides.

40
Q

Fatty acids

A
  • Have a CARBOXYL GROUP at the end which plays an important role when forming triglycerides.
  • The rest of the molecule consists of a long chain of C atoms bonded to H atoms.

SATURATED fatty acids ~ contain SINGLE C-C bonds only.

UNSATURATED fatty acids ~ have at least one DOUBLE C=C bond.

MONO unsaturated ~ contains only ONE
double C=C bond.

POLY unsaturated ~ contains MORE THAN ONE double C=C bond.

41
Q

Formation of a triglyceride

A
  • OH is lost from the glycerol
  • H is lost from the fatty acid
  • An OXYGEN links the two molecules together forming and ESTER BOND.
  • This process is known as ESTERFICATION.
  • Forms WATER so is known as a CONDENSATION REACTION.
  • When THREE bonds are formed this is known as a TRIGLYCERIDE.
42
Q

HYDROLYSIS REACTION in triglycerides

A
  • In the digestive system, lipase breaks the ester bonds.
  • This releases the glycerol and fatty acids.
  • This reaction requires THREE water molecules.
43
Q

Phospholipids

A

-Has a similar structure to TRIGLYCERIDES:
- One glycerol molecule bonded to two
fatty acids.

The glycerol molecule is also bonded to a PHOSPHATE:
-Negatively charged making this part of the molecule POLAR.
-This means the phosphate group is HYDROPHILIC ( it attracts water molecules).

44
Q

The phospholipid bilayer

A

HEAD - the polar , hydrophilic part of the molecule.

TAIL - represents the two fatty acid molecules which are non-polar and hydrophobic.

This means phospholipids contain both a hydrophilic and a hydrophobic region.

IN WATER:
- position themselves so that the hydrophilic head groups can interact with the water molecules.
- The hydrophobic tails CLUSTER together, well away from water molecules.

This is known as a PHOSPHOLIPID BILAYER.

USEFUL ~ it allows phospholipids to form the membranes that we find both AROUND & WITHIN cells

45
Q

Cholesterol

A
  • Part of a family of lipids called STEROLS.
  • The HYDROXYL GROUP is hydrophilic where as the rest of the molecule is hydrophobic.
  • This means cholesterol can INSERT into CELL MEMBRANES.
46
Q

The interaction of cholesterol and phospholipids

A
  • The HYDROPHILIC hydroxyl group on the cholesterol molecule can interact with the HEAD groups of phospholipids.
  • The rest of the cholesterol molecule can interact with the HYDROPHOBIC fatty acid tails.
47
Q

ROLES of cholesterol

A
  • Controlling the FLUIDITY of cell membranes.
  • Used as the starting point of a range of
    HORMONES :
    Oestrogen and testosterone can pass
    through the cell membrane and interact
    with their RECEPTORS inside the cell
  • Used in the body to make VITAMIN D:
    This takes place in the SKIN in response to
    UV light .Vitamin D is important for the
    proper development of BONES.
  • Used in the LIVER to produce BILE which increases the rate of digestion of lipids by the enzyme lipase.

Biology (6 decks)

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