1 Chemicals of life. 2015/9/9 2 The Macromolecules of cells

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Chemicals of life

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The Macromolecules of cells

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The Unique Water molecule

The water molecule is not linear

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V-shaped linear

Polarity and hydrogen bond

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Polarity and hydrogen bond

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Polarity and hydrogen bond

Result of regular arrangement of water molecules: ice crystals

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Peculiar Properties of water

A waterstrider / pond skater demonstrates how cohesion (H-bonds) between water molecules allow it to move across water's surface.

1. Universal Solvent

2. High heat capacity, heat of fusion, heat of vaporizaton

3. Density & Freezing properties

4. Surface tension

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Water- an universal solvent ----- for polar and charged particles

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Water and oil are immiscible.

“like dissolves like”

oil (long hydrocarbon chain, non-polar)

Vs

water (polar, H-bonding)

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Fatty substances form membrane compartments in cells to allow different reactions to take place independently of one another

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High heat capacity, high heat of vaporization and fusion

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High heat capacity, high heat of vaporization and fusion

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high heat of vaporization

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Cohesion in water molecule

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Cohesion and surface tension

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Cohesion and water transport in plants

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Ice is less dense than water

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What would happen to life in the lake when the lake is frozen?

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Water as a reactant

photosynthesis

digestion

Turgor and wilting Turgor loss in plants causes wilting

Which can be reversed when the plant is watered

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Water- the habitat for many life forms

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Minerals in DNA – P, N,

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Minerals in functional molecules – haemoglobin, chlorophyll

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Minerals : Iron containing haem in haemoglobin holds oxygen

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Minerals - calcium

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Minerals- nerve activities: ions movements _ Na+, K+

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Carbohydrates

Monosaccharides with different no. of Carbon

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Common Monosaccharides

Six-carbon sugars

Linear and Ring forms

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Alpha and beta form of glucose

Interconversion of Mono-- Di--polysaccharides

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Condensation / dehydration synthesis

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Disaccharides

Reducing and non-reducing sugars

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Test for reducing sugars

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Sugars are sweet! How sweet is it?

SugarRelative sweetness 

to sucrose

lactose 0.16

galactose 0.32

maltose 0.33

sucrose 1.0

fructose 1.73

aspartame 180                       

saccharin 450

Polysaccharide-starch

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helical structure of starch

Starch grains in plant cells

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Mitochondria Glycogen granules

0.5 µm

Glycogen

Glycogen: an animal polysaccharide

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Cellulose- a structural material

LE 5-7

a Glucose

a and b glucose ring structures

b Glucose

Starch: 1–4 linkage of a glucose monomers.

Cellulose: 1–4 linkage of b glucose monomers.

• Polymers with alpha glucose are helical• Polymers with beta glucose are straight• In straight structures, H atoms on one

strand can bond with OH groups on other strands

• Parallel cellulose molecules held together this way are grouped into microfibrils, which form strong building materials for plants

LE 5-8

Cellulosemolecules

Cellulose microfibrilsin a plant cell wall

Cell walls Microfibril

Plant cells

0.5 µm

Glucosemonomer

Enzymes that digest starch by hydrolyzing alpha linkages can’t hydrolyze beta linkages in cellulose

Cellulose in human food passes undigested through the digestive tract as insoluble fiber

Some microbes use enzymes to digest cellulose

Many herbivores, from cows to termites, have symbiotic relationships with these microbes

Chitin, another structural polysaccharide, is found in the exoskeleton of arthropods e.g insects

Chitin also provides structural support for the cell walls of many fungi

Chitin can be used as surgical thread

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Obesity

What are Lipids?

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The unifying feature of lipids is having little or no affinity for water

Lipids are hydrophobic -- becausethey consist mostly of hydrocarbons, which form nonpolar covalent bonds

The most biologically important lipids are fats, phospholipids, and steroids

LE 5-11a

Dehydration reaction in the synthesis of a fatGlycerol

Fatty acid(palmitic acid)

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A Triglyceride

Fats made from saturated fatty acids are called saturated fats

Most animal fats are saturated Saturated fats are solid at room

temperature A diet rich in saturated fats may contribute

to cardiovascular disease through plaque deposits

LE 5-12a

Saturated fat and fatty acid.

Stearic acid

Saturated and unsaturated fats

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Fats made from unsaturated fatty acids are called unsaturated fats

Plant fats and fish fats are usually unsaturated

Plant fats and fish fats are liquid at room temperature and are called oils

LE 5-12b

Unsaturated fat and fatty acid.

Oleic acid

double bondcauses bending

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Phospholipid

-replacing a fatty acid (nonpolar) with a phosphate

(polar)

Phospholipids- lipids with a polar head

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Lipid bilayer

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Lipid bilayer forms membrane

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The basic structure of testosterone (male hormone;睪固酮 ) and estradiol (female hormone;雌激素 ) is identical.

Both are steroids with four fused carbon rings, but they differ in the functional groups attached to the rings.

These then interact with different targets in the body.

Steroid tree

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Proteins have many structures, resulting in a wide range of functions

Proteins account for more than 50% of the dry mass of most cells

Protein functions include support, storage, transport, cellular communications, movement, body defense

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Amino acids – general formula

Variable properties

according to the R group

Amino acids - examples

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Peptide bond - dipeptide

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Amino Acid Polymers

Amino acids are linked by peptide bonds

A polypeptide is a polymer of amino acids

Polypeptides range in length from a few monomers to more than a thousand

Each polypeptide has a unique linear sequence of amino acids

Polypeptides

Polypeptides are polymers of amino acids

A protein consists of one or more polypeptides

Protein Conformation and Function

A functional protein consists of one or more polypeptides folded, and coiled into a unique shape

The sequence of amino acids determines a protein’s three-dimensional conformation

A protein’s conformation determines its function

A ribbon model

Groove

Groove

A space-filling model

Four Levels of Protein Structure

The primary structure of a protein is its unique sequence of amino acids

Secondary structure, found in most proteins, consists of coils and folds in the polypeptide chain

Tertiary structure is determined by interactions among various side chains (R groups)

Quaternary structure results when a protein consists of multiple polypeptide chains

Primary structure, the sequence of amino acids in a protein, is like the order of letters in a long word

Primary structure is determined by inherited genetic information

Typical secondary structures are a coil called a helix and a folded sheet structure

Amino acidsubunits

helix

pleated sheet

Tertiary structure is determined by interactions between R groups, rather than interactions between backbone constituents

These interactions between R groups include hydrogen bonds, ionic bonds, hydrophobic interactions, and van der Waals interactions

Strong covalent bonds called disulfide bridges may reinforce the protein’s conformation

Hydrophobicinteractions andvan der Waalsinteractions

Polypeptidebackbone

Disulfide bridge

Ionic bond

Hydrogenbond

Quaternary structure results when two or more polypeptide chains form one macromolecule

Collagen is a fibrous protein consisting of three polypeptides coiled like a rope

Hemoglobin is a globular protein consisting of four polypeptides: two alpha and two beta chains

Chains

ChainsHemoglobin

IronHeme

CollagenPolypeptide chain

Polypeptidechain

Sickle-Cell Disease: A Simple Change in Primary Structure

A slight change in primary structure can affect a protein’s conformation and ability to function

Sickle-cell disease, an inherited blood disorder, results from a single amino acid substitution in the protein hemoglobin

LE 5-21a

Red bloodcell shape

Normal cells arefull of individualhemoglobinmolecules, eachcarrying oxygen.

10 µm 10 µm

Red bloodcell shape

Fibers of abnormalhemoglobin deformcell into sickleshape.

LE 5-21b

Primarystructure

Secondaryand tertiarystructures

1 2 3

Normal hemoglobin

Val His Leu

4Thr

5Pro

6Glu Glu

7Primarystructure

Secondaryand tertiarystructures

1 2 3

Sickle-cell hemoglobin

Val His Leu

4Thr

5Pro

6Val Glu

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Quaternarystructure

Normalhemoglobin(top view)

Function Molecules donot associatewith oneanother; eachcarries oxygen.

Quaternarystructure

Sickle-cellhemoglobin

Function Molecules interact withone another tocrystallize intoa fiber; capacityto carry oxygenis greatly reduced.

Exposedhydrophobicregion subunit subunit

What Determines Protein Conformation?

In addition to primary structure, physical and chemical conditions can affect conformation

Alternations in pH, salt concentration, temperature, or other environmental factors can cause a protein to unravel

This loss of a protein’s native conformation is called denaturation

A denatured protein is biologically inactive

Protein – internal Forces/ bonding

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LE 5-22

Denaturation

Renaturation

Denatured proteinNormal protein

Protein – What level of protein structure is represented below?

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Protein – Levels of complexity

Protein – globular proteinsproteins with physiological function

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Globular protein e.g. enzyme

Protein – globular proteins: e.g. antibodies

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Structural proteins

Protein – Fibrous proteins with structural function e.g. collagen

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