B1.1 Carbohydrates

What are covalent bonds?

When valence electrons are shared between two non-metal elements.

Why are electrons shared between atoms?

To generate strong bonds between compounds

Which four major categories of biological molecules is carbon present in?

Carbohydrates, Lipids, Proteins, Nucleic acids

How many electrons does carbon have in its outer shell?

Four

How many covalent bonds can one carbon atom form?

Four

Which two atoms does carbon usually form covalently-bonded compounds with?

Hydrogen and oxygen

What can carbon compounds form?

Chains, branches, rings, double bonds

What are functional groups?

Groups of atoms that are found in organic compounds (contains carbon)

What are examples of functional groups?

Hydroxyl, Carboxyl, Amino, Phosphate groups

What is the role of functional groups?

Add chemical reactivity to the carbon backbone, give organic compounds their individual properties

What are monomers?

Molecules which join to other similar molecules to form polymers

What are polymers?

Molecules made from a large number of monomers joined together in a chain

What is the process of polymerisation?

When monomers join to form polymers 

What are macromolecules?

Contain 1000 or more atoms and have a high molecular mass

What are condensation reactions?

When molecules combine together, forming covalent bonds and resulting in polymers or macromolecules. Water is removed

How are polysaccharides formed?

By condensation reactions, when two hydroxyl (OH) groups on different monosaccharides interact to form a strong covalent bond (glycosidic bond)

What is a glycosidic bond?

A strong covalent bond linking a sugar (carbohydrate) molecule to another group

How are polypeptides formed?

By condensation reactions, when two amino acid monomers interact to form a strong covalent bond called a peptide bond

What are peptide bonds?

Strong covalent bonds that links amino acids together

What are phosphodiester bonds?

Strong covalent bonds where a phosphate group connects the 3' carbon of one sugar to the 5' carbon of another sugar. Consist of a phosphate group and two ester bonds

What bond does this image show?

Glycosidic bond

What bond does this image show?

Peptide bond

What bond does this image show?

Phosphodiester bond

What are hydrolysis reactions?

Covalent bonds in polymers are broken into monomers when water is added

What are monosaccharides?

Simple sugars with 3-7 carbons, mostly ring forms

What are some properties of monosaccharides?

Colourless crystalline molecules, soluble in water

What are the isomers of glucose?

Alpha (α) glucose and beta (β) glucose

Which polysaccharides are made from alpha glucose?

Starch and glucose

Which polysaccharides are made from beta glucose?

Cellulose

How does glucose have a stable structure?

The presence of covalent bonds which are strong and hard to break

How is glucose soluble in water?

It is polar

How is glucose easily transportable?

Soluble in water

How is glucose a source of chemical energy?

When its chemical bonds are broken, up to 36 ATP molecules are released

What is the function of carbohydrates?

Energy storage molecules and structural molecules

What are polysaccharides composed of?

Many sugar molecules combined through a series of condensation reactions or removed by hydrolysis reactions.

What is the polysaccharide that serves as a store of energy in plants?

Starch

What is the polysaccharide that serves as a store of energy in animals and fungi?

Glycogen

Why are starch and glycogen effective storage polysaccharides?

They are:

1. Compact - large quantities can be stored in a small space

2. Insoluble - soluble molecules will dissolve in cytoplasm, causing water to move inside and the cell to burst

Why is cellulose a structural polysaccharide?

It is:

1. Strong and durable

2. Insoluble and slightly elastic

3. Chemically inert

What 2 polysaccharide molecules is starch composed of?

Amylose and amylopection

What is amylose?

Unbranched helix-shaped chain with 1,4 glycosidic bonds between alpha glucose molecules

What is amylopectin?

Branched molecule with 1,4 and 1,6 glycosidic bonds between alpha glucose molecules

What is glycogen?

Branched molecule with 1,4 and 1,6 glycosidic bonds between alpha glucose molecules

Why is glycogen more branched than amylopection?

It has more free ends where glucose can be removed by hydrolysis so it can be broken down quickly

What is cellulose?

Straight unbranched polysaccharide with beta glucose molecules

What is the structure of cellulose?

Every alternate molecule of beta glucose is inverted to allow hydrogen bonding to occur between strands

What are microfibrils?

Groups of cellulose molecules held together by hydrogen bonds.

What is the function of cellulose microfibrils?

Maintains structural integrity of plants cell walls due to high tensile strength

What are glycoproteins?

Integral proteins within phospholipid bilayers with a chain of carbohydrates attached that can act as an antigen

How are glycoproteins formed?

When carbohydrates and polypeptides combine via covalent bonds

How do glycoproteins aid cell to cell adhesion?

They interact with glycoproteins on neighbouring cells, allowing the formation of tissues

How do glycoproteins act as receptors for hormones?

When a hormone binds to a specific glycoprotein receptor, it changes metabolism within the cell

How do glycoproteins aid cell to cell communication?

Neurotransmitters bind to glycoproteins.

How do glycoproteins aid immune responses?

Glycoproteins act as markers on cells allowing the immune system to distinguish between self and non-self cells

What are antigens?

Substances which stimulate an immune response and the production of antibodies