Biology - B1.1 Carbohydrates and Lipids

Monomer

single units, one molecule that can be used to form dimers and polymers

• e.g. amino acid, glucose (monosaccharide), fatty acid

Dimers

Two single units, two monomers bonded together

For carbohydrates, it’s disaccharides, and for proteins, it’s dipeptides

Polymers

Three or more single units, three or more monomers bonded together. Can be different monomers bonded together

For carbohydrates, it’s polysaccharides, and for protein, it’s polypeptides

Why is life based on carbon?

• all biological molecules require carbon (e.g. DNA and enzymes)

• carbon is useful because it requires four covalent bonds and then an enormous variety of molecules can be formed (rings, chains or branches)

Macromolecules

Very large molecules, they are all polymers so they are made up of many monomers. The official limit for a macromolecule is more than 10,000 atomic mass units.

What is a condensation reaction?

The joining of two molecules together with the release water by removing a hydroxyl group and an extra hydrogen.

• Energy is required for this reaction in the form of ATP, endothermic reaction

Anabolic reactions

Reactions that build up larger molecules from smaller molecules

Why is water made during a condensation reaction?

The available elements are H₂ and O_2, and H₂O₂ is toxic, whilst H₂ would make the cells too acidic.

The water formed usually turns into the cytoplasm or exits through osmosis. 

Hydrolysis reaction

• Literally means ‘water split’

• Opposite of condensation reaction 

• A water molecules is used and split to provide the hydroxyl group and hydrogen that are needed to form new bonds. 

• Exothermic reaction because energy is released in the form of ATP or thermal energy

Function of hydrolysis reactions

Used to deconstruct polymers into monomers as an energy source or to create new molecules. Mainly used during digestion.

Catabolic reactions

• Destruct bonds

• Hydrolysis reactions are catabolic

What bond is made after condensation for carbohydrates?

1→ 4glycosidic bonds, covalent bonds, because they are made between two glucoses and between the 1st and 4th carbon

What are the monomers of carbohydrates called?

Monosaccharides

What is a hexose monosaccharide?

A monomer of carbohydrates with 6 carbons, in the shape of a hexagon, with oxygen in the top right angle and the sixth carbon added on the top left.

e.g. glucose or fructose 

Pentose monosaccharide

A monomer of carbohydrates with 5 carbons, in the shape of a pentagon, with oxygen in the top center angle and the sixth carbon added on the top left.

e.g. ribose or deoxyribose

Functions of monosaccharides

• soluble and then easily transportable

• chemically stable so can be stored easily without changing form

• good source of energy for aerobic or anaerobic respiration

Polysaccharides

Carbohydrates with many monosaccharides joined together

Function of polysaccharides

They are insoluble and are then incredibly good energy sources

Two types of starch

Amylose and amylopectin

What is starch?

• Polymer of glucose

• Used as storage of glucose for energy because of it’s compact storage and insolubility

• Found in plants

Amylose

• Monomer: alpha glucose

• Bonds: 1→ 4 glycosidic bonds

• Shape: unbranched chain of alpha glucose with a helical shape due to the 1→ glycosidic bonds because they cause an angle between the two monomers

• Function: energy storage in plants

Amylopectin

• Monomer: alpha glucose

• Bonds: 1→ 4 glycosidic bonds and some 1→ 6 glycosidic bonds

• Shape: chain of alpha glucose with a helical shape and some branches

• Function: energy storage in plants. the branches make it the glucose more accessible because there are more ends

Glycogen

• Monomer: alpha glucose

• Bonds: 1→ 4 glycosidic bonds and (1 in 10) 1→ 6 glycosidic bonds

• Shape: chain of alpha glucose with a helical shape and many branches

• Function: energy storage in animals. the many branches make the energy easily accessible

Function of cellulose

Strong structure/material for cell wall

What is the monomer for cellulose?

beta glucose

What is the structure of beta glucose?

Beta glucose is different from alpha glucose because the hydroxyl groups are on opposite structures for beta glucose. The OH and H are reversed at the first carbon.

Why does the structure of cellulose help its function?

Cellulose is made up of beta glucose so every other beta glucose has to flip in order to maintain the 1→ 4 glycosidic bonds 

As the monomers flip, the angles of the bonds cancel out and result in a straight chain. 

The straight chains can then easily be stacked on top of each other and hydrogen bonds are created between the OH and H of the beta glucose monomers.

These hydrogen bonds make cellulose stronger than any other polysaccharide, helping its function.

Glycoprotein

Def: molecules with both a carbohydrate and a protein part

Particularly common in animal cell membranes

The carbohydrate part sticks out of the cell membrane and acts as a recognition site for other cells

Oligosaccharide

3-15 monosaccharides

What are the three types of glycoproteins?

A, B and O

Structure of A, B and O glycoproteins

A has 5 monosaccharides with the first four being the same base as the other glycoproteins

B has 5 monosaccharides with the first four being the same base as the other glycoproteins, different than A

O has 4 monosaccharides, all four being the same base as with A and B

Antigens

The glycoproteins A and B are called antigens as they stimulate an immune response (depending on the blood type of the person)

How are A, B and O glycoproteins useful during blood transfusions?

The A, B and O glycoproteins show what type of blood would be rejected by the body as it is foreign.

O is the universal donor as it has the same base as A & B. If the blood type is O, only O can be transfused.

If someone has blood type AB, any blood can be given; no glycoproteins will be considered foreign.

What are the types of lipids?

Fats, oils, waxes and steroids

Are lipids hydrophobic or hydrophilic?

They are said to be hydrophobic however, they solely prefer non-polar substances, and then mostly dissolve in non-polar substances.

This is because lipids contain less oxygens which are slightly electronegative meaning they have less polarity.

What is the melting point for oils?

Around 18 degrees Celsius or below room temperature

What is the melting point for fats?

Above room temperature but below 37 degrees Celsius

What is the melting point of waxes?

Above 37 degrees celsius

What is the structure of steroids?

They have four fused carbon rings (characteristic four-ring structure)

Structure of triglycerides

• One glycerol and three fatty acids though the structure of the fatty acid can vary

• Are formed by condensation reactions as the OH of a the carboxyl group of the hydrocarbon chain can react with one of the hydroxyls of the glycerol

• 3 waters molecules are produced

• Ester bonds are the bonds connecting the fatty acids to the glycerol

Structure of fatty acids

• Carboxyl group at one end (COOH) and then a hydrocarbon chain and a methyl group at the end (CH₃)

• COOH(CH₂)_nCH₃ is the general formula of a fatty acid

• variations with the presence, position and number of double bonds and the length of the hydrocarbon chain

Compare and contrast the bond formed between the fatty acid and the glycerol with the bond between two monosaccharides

Ester bond vs. glycosidic bond, both are made through a condensation reaction

What are the two categories of fatty acids?

Saturated fatty acid vs. unsaturated fatty acid (cis or trans fatty acids)

Saturated fatty acid

Fatty acids that have single bonds between every carbon on the hydrocarbon chain

General formula of C_nH_2nO₂

Unsaturated fatty acids

Fatty acids with one or more double bonds in the hydrocarbon chain

• Either cis or trans depending on where the hydrogens of the carbons that have the double bond are positioned

Cis unsaturated fatty acids

The hydrogens connected to the carbons of the double bond are on the same side

So they bend at the double bend

So they are less easy to stack and have a lower melting point and are liquid at room temperature, oils

What type of fatty acids do animals store their lipids as?

Saturated fatty acids

What type of fatty acids do animals store their lipids as?

Unsaturated cis fatty acids

Unsaturated trans fatty acids

The hydrogens connected to the carbons with the double bond are on the same side

So they are straight-chained and have a higher melting point and are solid at room temperature 

They are produced artificially

Monounsaturated vs. polyunsaturated fatty acids

Monounsaturated fatty acids have one double bond whilst polyunsaturated fatty acids have two or more

What group of cells are triglycerides stored in in animals?

Adipose tissue, which is located beneath the skin and around organs

What are the advantages of triglycerides being stored in adipose tissue?

• Chemically stable, so the lipids don’t get involved in reactions

• The lipids don’t dissolve so don’t have any effect on the solute concentration and osmosis

• Lipids release twice as much energy per gram than carbohydrates so double the energy can be stored in half the body-mass

• Poor conductors, so excellent thermal insulators

• Liquid at body temperature so they can absorb shock

Compare and contrast carbohydrates and lipids as energy storage compounds

Both are used in energy storage

• Carbs is short term while lipids is long term

• Carbs can be mobilized easily while lipids takes longer to mobilise

• Carbs are soluble and then easily transportable while lipids are insoluble and harder to transport

• Carbs release less energy per gram while lipids release double the energy per gram

• Carbs can be used in both aerobic and anaerobic respiration while lipids can only be used in aerobic respiration

Phospholipids

Structure: have a section that is hydrophobic (the fatty acids, the tail) and a section that is hydrophilic (the phosphate group and the glycerol, the head)

Therefore, amphipathic, although the hydrophobic part has more effect as the tails are longer in comparison to the head

Amphipathic

When one part of a molecule is hydrophobic while another is hydrophilic

Structure of cell membrane

Phospholipid bilayer with phospholipids arranged in two layers, the heads are faced towards the inside the cell and towards the solution outside, the tails are all pointing inwards

Phospholipid bilayer

Two layers of phospholipids, both hydrophobic and hydrophilic with the hydrophobic tails facing inwards

Steroids easily passing through a cell membrane

They can easily pass through a cell membrane because they are considered hydrophobic because they are made of mostly hydrocarbons

This is useful as steroids regulate many levels and reactions