Biological Molecules Flashcards
Polysaccharides
Polysaccharides
Polysaccharides contain monosaccharides. They are formed by condensation reactions linked by glycosidic bonds.
Mainly used as energy stores and structual components of cells.
Major polysaccharides include starch and cellulose in plants and glycogen in animals.
Starch
Starch is a polymer of the monomer alpha glucose. It is insoluble making it non affecting water potential. It is in a helical shape because as polymers form they twist and become compact.
What does starch contain
Starch has different relative amounts of AMYLOSE and AMYLOPECTIN.
However the amount of amylopectin in starch is generally about 70/80 percent.
Amylose features
Amylose
• 1-4 glycosidic bonds
• Unbranched chains
• Helical structure \
Amylopectin
Amylopectin
• 1-4 and 1-6 glycosidic bonds
• Highly branched chains
Amylopectin
Amylopectin
• 1-4 and 1-6 glycosidic bonds
• Highly branched chains
Where is starch stored
Starch is a major carbohydrate in plants.
It is usually stored as intracellular starch grains in organelles called plastids. The plastids include green chloroplasts and colourless amyloplasts.
Purpose of starch
Starch is produced from glucose made during photosynthesis it is broken down during respiration to provide energy as a source of carbon for producing other molecules.
Features of cellulose
Unlike starch, cellulose is very strong and prevents cells from bursting.
They are long chains of beta glucose. Joined by 1-4 beta glycosidic bonds.
The glucose chains join together hydrogen bonds which form chains from rope like microfibres which are layered to form a network.
The more hydrogen bonds, the stronger the chains are.
What is cellulose
Cellulose is another polysaccharide is mainly part of cell walls and is the most abundant organic polymer. It is beta glucose.
Hydrogen bonds in cellulose
Hydrogen bonds give molecules great tensile strength which is ideal for providing structual support to plant cells.
Hydrogen bonds then form between chains via the OH group to form microfibres and cellulose fibres.
Very rigid which is ideal for structual components such as plant cell walls.
Where is glycogen stores
Glycogen is stored as small granules particularly muscles and liver. It is less dense and soluble. It is broken down motr rapidly which indicates higher metabolic requirements of animals compared with plants.
Where are glycogen found
These branches of glucose form glycogen grains which are found in cytoplasm of muscle and liver cells.
Features of glycogen
Animals do not store carbohydrates as starch but glycogen. Glycogen has similar structure to amylopectin containing alpha 1-6 glycosidic bonds that produce even more of the branched structure.
Properties of lipids
Properties of lipids:
• made up of carbon, hydrogen and oxygen
• Proportion of carbon to oxygen and hydrogen is smaller than carbohydrates.
• Insoluble in water
• Soluble in organic solvents such as alcohol and acetone
Roles of lipids
Roles of lipids
• contribute to flexibility to cell membranes
• Source of energy
• Waterproofing
• Insulation
• Protection
What are triglycerides
Contain 3 fatty acids and 1 glycerol. They are produced from a condensation reaction and form an ester bond. They are formed from carboxillic acids giving it a acidic property. The ester comes from the fat and the glycosidic is the saccharide (sugar).
Whatfunctional group does fatty acids contain
There are over 70 different fatty acids and they all have the COOH carboxillic acid group with a hydrogen chain attached.
The length of chain determines how saturated the fat is. The more double bonds in the tail means the more unsaturated the fat is.
Phospholipids
Similar to lipids except for one of the fatty acid molecules is replaced by a phosphate molecule. The fatty acid molecules repel water (hydrophobic) whereas the phosphate molecules attract water (hydrophilic)
Energy in lipds
The high ratio of energy strong carbon-hydrogen bonds to carbon atoms and are therefor excellent source of energy.
There is a low mass to energy ratio making them good storage molecules because much energy can be stored in a small volume.
Triglycerides in water
Being large non-polar molecules, triglycerides are insoluble in water. As a result, their storage does not affect osmosis in cells or the water potential of them.
As they have a high ratio of hydrogen to oxygen atoms triglycerides release water when oxidised and therefore provide an important source of water especially for organisms in dry deserts
How many amino acids are in the body
There are over 20 amino acids found in biology.
What are the two sulphyr containing amino acid
There are only two sulphur containing amino acids, these include cysteine and methionine. The sulfur atoms in the cysteine molecules can form a covalent bond. This is a disulphide bonds. Not broken by high temps or ph changes
What is a polypeptide
If we join three or more amino acids, we make a polypeptide. One molecule of water is formed from every peptide formed.
We can reverse this reaction and break the peptide bond by hydrolysing the molecule (adding water) which can be done by protease in the digestive system.
What is the difference between the polypeptide and the protein?
A polypeptide has to fold into a complex 3d shape to carry out its function - we would refer to it as a protein molecule
Primary structure in proteins
The sequence of amino acids bonded by covalent peptide bonds is the primary structure of a protein
DNA of a cell determines the primary structure of a protein by instructing the cell to add certain amino acids in specific quantities in a certain sequence.
This affects the shape and the function of the protein.
The primary structure is specific for each protein.
Tertiary structure in proteins
Further conformational change of the secondary structure leads to additional bonds forming between the R groups (side chains)
The additional bonds are:
- Hydrogen (these are between R groups)
- Disulphide (only occurs between cysteine amino acids)
- Ionic (occurs between charged R groups)
- Weak hydrophobic interactions (between non-polar R groups)
This structure is common in globular proteins
Quaternary structure in proteins
Occurs in proteins that have several polypeptide chain working together as a functional macromolecule.
Each polypeptides are called subunits by scientists.
The quaternary structure shows how the individual subunits are arranged to form a larger three dimensional structure.
Also shows position of any prosthetic groups.
Prosthetic Groups
Some proteins contain other non protein molecules forming part of the structure.
These are called prosthetic group which help carry out their function.
Proteins with a prosthetic group are called conjugated proteins.
What happens when mutations occur
if it mutates the protein base may function, some can cause catastrophic and some may have little impact.
Bonding in proteins - Hydrogen bonds
They fold so hydrophilic groups are on the outside and hydrophobic groups are on the inside.
Some R groups are polar so the hydrogen bond may form between them.
Due to the slight positive and negative charges on the hydroxyl, the bond can form between R groups.
Weak bonds and easily broken by PH or temperature changes.
Disulphide bonds - bonding in protein
Disulfide bonds are strong covalent bonds that form between two cysteine R groups (as this is the only amino acid with an available sulfur atom in its R group)
These bonds are the strongest within a protein, but occur less frequently, and help stabilise the proteins
These are also known as disulfide bridges
Can be broken by reduction
Disulfide bonds are common in proteins secreted from cells eg. insulin
Bonding protein - Ionic bonds
Ionic bonds form between positively charged (amine group -NH3+) and negatively charged (carboxylic acid -COO-) R groups
Ionic bonds are stronger than hydrogen bonds but they are not common
These bonds are broken by pH changes
Bonding proteins - Hydrophobic reactions
between non polar side chains. Several amino acids are not charges so are called non polar.
Hydrophobic R groups tend to cluster together to exclude water molecules.
Hydrophobic interactions form between the non-polar (hydrophobic) R groups within the interior of proteins
Globular proteins
Globular proteins form a spherical mass with (tertiary) a specific 3D shape and a quaternary. They are soluble in water. They contain hydrophilic amino acids on their surface which will interact with water molecules making them soluble. Hydrophobic amino acids are deep in the centre of the protien.
How does haemoglobin bond with oxygen
The presence of the haem group (and Fe2+) enables small molecules like oxygen to be bound more easily because as each oxygen molecule binds it alters the quaternary structure (due to alterations in the tertiary structure) of the protein which causes haemoglobin to have a higher affinity for the subsequent oxygen molecules and they bind more easily
What subunit does haemoglobin contain
The prosthetic haem group contains an iron II ion (Fe2+) which is able to reversibly combine with an oxygen molecule forming oxyhaemoglobin and results in the haemoglobin appearing bright red
Making haemoglobin an example of a conjugated protien.
What structure is haemoglobin
It has a quaternary structure as there are four polypeptide chains. These chains or subunits are globin proteins (two α–globins and two β–globins) and each subunit has a prosthetic haem group.
What is collagen
Collagen is the most common structural protein found in vertebrates
In vertebrates it is the component of connective tissue which forms
Collagen is an insoluble fibrous protein
Why is collagen insoluble
They have a large proportion of amino acids with hydrophobic R groups makes them insoluable in water which makes them useful for structure and support.
