Section 5: Molecules of Life - Macromolecules

Organic molecules – contain carbon and hydrogen atoms

A) Type of macromolecules

4 types:

Name subunit

Carbohydrates monosaccharides

Lipids Glycerol + 3 fatty acids

Proteins Amino acids

Nucleic acids nucleotides

B) Chemical reactions -forms macromolecules and takes them apart:

Dehydration synthesis

Subunits + subunit macromolecule + H2O

Hydrolysis

Dehydration synthesis -making macromolecules from subunits - Water is

given off

Hydrolysis – macromolecules break apart in presence of water to re-form

subunits

C) Carbohydrates

i. Why group these molecules?

Characterized by presence of this molecule grouping

H – C – OH (CHO)

Ratio of H to O is approximately 2 to 1 – same as with H2O (water) so

that’s why they are called hydrates of carbon – carbohydrates

ii. Function

used for quick and short term energy storage in cells.

iii. Types of carbohydrates

1. Simple carbohydrates

a. Monosaccharides – 3 to 7 carbons (1

ring) i.e.; glucose –6 carbon sugar

b. Disaccharides – 2 monosaccharides joined

together by dehydration

Synthesis ie. Maltose

2. Complex carbohydrates (aka polysaccharides)

More than 2 sugar molecules joined together

Macromolecules such as starch, glycogen, and cellulose contain many

1000’s of glucose units

Starch – from plant material, stored glucose units

Glycogen – from animal material, stored in liver by animals for short

term storage of glucose between meals

D) Lipids

i. Why group these molecules?

Do not dissolve in water - hydrophobic

ii. Function

Diverse functions

Some as hi energy storage molecules -more energy/gram than any other

macromolecule

Phospholipids –cell membranes

steroids –diverse function including hormones

iii. Types of Lipids

1. Fats and Oils

2. Phospholipids

3. Steroids

1. Fats and Oils

Composition:

Composed of glycerol + 3 fatty acids Lipid

Alcohol molecule long chain hydrocarbons with COOH

(organic acid)

+

=

also called triglyceride

Function:

Long term energy storage

Insulates against heat loss

Protective cushion around major organs

Fatty Acid types in Fats and Oils

Saturated

No double bonds between carbon atoms

Associated with cardiovascular disease because causes plaque buildup in

arteries

Unsaturated

double bonds between carbon atoms in carbon chain (wherever the # of H

is less than 2 per carbon)

Polyunsaturated fats

many double bonds between carbon atoms in carbon chain

Trans fats

chemically hydrogenated oils - semi solid - unhealthy

2. Phospholipids

Composition:

**important in forming cell membranes

Because polar hydrophilic (water loving) head and nonpolar

hydrophobic (water hating) tails: form spontaneous bilayer

in water

Bilayer (=2 layers)

Hydrophobic tails face inward and form hydrophobic interior

Hydrophilic heads face outwards towards H2O

3. Steroids

Specialized lipids with backbone of 4 fused carbon rings – the functional

group that is attached to this backbone is what makes each steroid

different from each other.

Several functions, mainly hormonal ie, testosterone and estrogen

Affect 2o sexual characteristics

E) Proteins -

essential in the structure and function of our cells.

i. Why group these molecules?

a name to describe a group of macromolecules with a certain structure (to

be described below) – with varied functions.

ii. Function

1. Support: structural proteins i.e., keratin, collagen, and elastin. Keratins

strengthen protective coverings such as hair, quills, feathers, horns, and

beaks. Collagens and elastin provide support for connective tissues such as

tendons and ligaments.

2. Enzymes: provides location for reactants to come together and speed up

chemical reactions in cells: often referred to as catalysts because they

speed up chemical reactions. i.e, lactase and pepsin. Lactase breaks down the

sugar lactose found in milk. Pepsin is a digestive enzyme that works in the

stomach to break down proteins in food.

3. Transport: channel and carrier proteins in plasma membrane allow transport

of ions and molecules into and out of cells. –i.e., carrier proteins move

Amino group

Acid group

R stands for the functional group – this is the part that is different for each amino acid – there are 20 different types of aa in humans

molecules from one place to another in the body. i.e hemoglobin – carries

oxygen in blood

4. Defence: antibodies formed by immune system combine with antigens: involved

in defending the body from antigens (foreign invaders). One way antibodies

destroy antigens is by immobilizing them so that they can be destroyed by

WBC.

5. Hormones: regulatory proteins: messenger proteins which help coordinate

certain bodily activities. i.e, insulin, oxytocin, and somatotropin. Insulin

regulates glucose metabolism by controlling the blood-sugar concentration.

Oxytocin stimulates contractions in females during childbirth. Somatotropin is

a growth hormone that stimulates protein production in muscle cells.

6. Movement: contractile proteins in muscle cause movement - responsible for

movement. i.e, actin and myosin. -involved in muscle contraction and

movement.

Video: protein function Youtube...uploaded by mikedolding?

iii. Structure of proteins

1. Subunits of proteins = Amino Acid

General structure– all proteins have this basic structure and an R group that makes

each amino acid unique.

carboxylic acid (type of organic acid)

2. Peptides:

2 amino acids join together in a dehydration synthesis rxn- the resulting

molecule is then called a peptide.

Polpeptide = many peptides= many joined amino acids

iv. Dehydration synthesis –formation of a peptide bond

dehydration

Hydrolysis

v. Shapes of proteins

Protein function depends on it attaining its final 3D shape this shape

determines how it binds to other molecules – fits like lock and key with

other molecules

If exposed to extreme heat or pH, proteins become denatured= becomes not

natural –loses natural 3D shape, so it no longer can fit into the lock and key

idea of other molecules – so it can no longer function like it should – they

lose both their secondary and tertiary structure

H

Bonding between R groups in aa is disturbed – in the tertiary structure –

which is its final shape – the bonding between the R groups breaks and

therefore the protein loses its shape

Causes irreversible change in shape of protein and therefore function: i.e.

Boiling eggs If proteins in a living cell are denatured, this results in

disruption of cell activity and possibly cell death.

vi. Levels of protein organization:

Level Shape Bonding

Primary 1o Linear chain of aa Peptide bonds between aa

Secondary 2o Helix (coiling)

Pleated sheet (folding)

Hydrogen bonds between

aa

Tertiary 3o globular Final 3D shape and

function: Ionic, covalent,

hydrogen bonds btwn R

groups

Quaternary (rare) 4o All shapes All bonding – 2 or more

associated polpeptides

1. Primary

= amino acids in a line (linear) – joined together by peptide bond

H O H H

H2N C C N C COOH

R OH H R

Peptide bond

Acid end of one amino acid bonds to the amine group of the next aa; Acid

end is negative, amine end is positive - Therefore polar

A Polypeptide = many peptides= many joined amino acids.

2. Secondary =helix coil (right handed spiral) or pleated sheet

linear chain takes on 3D shape

Hydrogen bonds hold 3D shape in place – bond between slightly + H end, and

other δ - atoms

In an alpha-helix, the protein chain is coiled like a loosely-coiled spring. The

"alpha" means that if you look down the length of the spring, the coiling is

happening in a clockwise direction as it goes away from you.

In a beta-pleated sheet, the chains are folded so that they lie alongside

each other

3. Tertiary Structure =globular structure = final 3D shape

held in place by covalent or ionic or hydrogen bonding between R groups.

held together by interactions between the side chains - the "R" groups

Hydrophilic parts are outside and hydropobic parts on the inside

*Important for structure

The 3o structure of a protein is the way the whole chain (including the 2o

structures) folds itself into its final 3-dimensional shape.

4. Quaternary structure

only for some proteins – when several polypeptides with their own 1o, 2o, 3o

structure bonds together

i.e, haemoglobin and enzymes

F) Nucleic Acids

essential in the structure and function of cells. Scientists who first discovered

them called them nucleic acids because they found them in the nucleus of the cell

i. Why group these molecules?

Nucleic acids are either DNA- deoxyribonucleic acid, or RNA – ribonucleic

acid

Both have subunit of a sugar+phosphate+base

ii. Function

DNA -deoxyribonucleic acid

stores genetic information –called genes – like a code

DNA replicates and transmits this genetic info during cell reproduction

Genes (the genetic info) specify the sequence of aa in the proteins (if this

is faulty will cause genetic faults –i.e. sickle cell anemia –where red blood

cells are misshapen and clog blood vessels leading to all sorts of problems)

RNA – ribonucleic acid

Is the intermediary that transmits the code regarding the aa sequence

in a protein – RNA is the nucleic acid directly involved in protein

synthesis

DNA is the keeper of the code, when needed it unravels and passes the code onto a

single strand of RNA – the RNA uses this code to make a protein. In a later

chapter, we describe how this happens.

iii. Structure of DNA and RNA

Both have nucleotide subunits

A Nucleotide is a molecular complex of 3 types of subunit molecules:

Phosphate, (Pentose) 5 C sugar, and nitrogen base

Linear chains of nucleotides form as phosphate and sugar backbone forms

between each nucleotide bonding together

RNA and DNA are polymers of nucleotides

DNA RNA

Double strand, double helix single strand

Sugar = deoxyribose sugar = ribose

4 nitrogen bases 4 nitrogen bases

Adenine (A) A

Thymine (t) Uracil (U)

Guanine (G) G

Cytosine (C) C

Nucleotides join to form a polynucleotide – called a strand

In DNA 2 strands twist around each other to form a double helix **Held

together by hydrogen bonds between bases

Complementary base pairs

A with T

G with C

have shapes that fit together

These complimentary base pairs allow DNA to replicate in a way that ensures the

sequence of bases will remain the same –it is like a code - this is important

because it is the sequence of bases that determine the sequence of aa in a protein.

it will not function if it isn’t correct.

iv. Specialized nucleotide – ATP Adenosine Triphosphate

ATP =adenosine triphosphate –special because normal structure of a

nucleotide is 1 phosphate, a sugar and a nitrogen base, ATP has 3

phosphates and the base is always adenine.

ATP = adenine + ribose (sugar) + 3 phosphate groups

ATP is an energy carrier in cells – hi energy molecule – the hi energy is

carried in the phosphate bonds

When ATP is broken down you get ADP (adenosine diphosphate) and when

the phosphate bond breaks between the ADP and the phosphate group that

breaks off, you get energy released.

Energy is used in cellular metabolism to synthesize macromolecules (such as

carbohydrates and proteins), in muscle cells the energy is used for muscle

contraction, and in nerve cells it is used for conduction of nervous impulses

After ATP breaks down it can be recycled by adding phosphate to ADP – an

input of energy is required to reform ATP

ATP is formed from the breakdown of glucose – glucose is used as energy

storage until required by the cell

A glucose molecule contains too much energy to be used as a direct source in

cell reactions. Instead the nrg of glucose is converted to ATP.ATP has an

amount of nrg that a cell can use to supply chemical reactions in cells.