021113 Chapter3 Revised RNA

8/21/2019 021113 Chapter3 Revised RNA

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Chapter 3 Learning Objectives

To understand why carbon is so important in

biological molecules To understand how organic molecules are

synthesized

To understand what carbohydrates, lipids,

proteins, nucleotides and nucleic acids are


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Why Is Carbon So Important in Biological Molecules?

What does organic mean?

Organicrefers to molecules containing a carbon

skeleton bonded to hydrogen atoms

Inorganicrefers to carbon dioxide and all molecules

without carbon

The carbon atom is versatile because it has 4 electrons

in an outermost shell

Organic molecules can assume complex shapes
http://www.google.com/url?sa=i&rct=j&q=carbon+atom&source=images&cd=&cad=rja&docid=sBiWULRxircZjM&tbnid=IJKqr9MhTH0UYM:&ved=0CAUQjRw&url=http%3A%2F%2Fen.wikipedia.org%2Fwiki%2FCarbon&ei=DYQJUYPLFo662gXp-4HgBA&bvm=bv.41642243,d.aWM&psig=AFQjCNF3clR5dkhfSd4SQ-8HdoYOFagxFw&ust=1359664489583896


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Functional groupsin organic molecules determine the characteristics

and chemical reactivity of the molecules

Functional groups are less stable than the carbon backbone and aremore likely to participate in chemical reactions


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How Are Organic Molecules Synthesized?

Small organic molecules (called monomers) are joinedto form longer molecules (called polymers)

Biomolecules are joined or broken through dehydrationsynthesis or hydrolysis

Monomers are joined together through dehydrationsynthesis, at the site where an H and an OH are

removed, resulting in the loss of a water molecule(H2O)

The openings in the outer electron shells of the twosubunits are filled when the two subunits share

electrons, creating a covalent bond


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Polymers are broken apart through hydrolysis

(water cutting) Water is broken into H and OH and is used to

break the bond between monomers

Hydrolysis

hydrolysis


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All biological molecules fall into 1 of 4 categories

Carbohydrates Lipids

Proteins

Nucleotides/nucleic acids


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Table 3-2 (1 of 2)


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Table 3-2 (2 of 2)


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What Are Carbohydrates?

Carbohydratemolecules are composed of C,

H, and O in the ratio of 1:2:1 If a carbohydrate consists of just 1 sugar

molecule, it is a monosaccharide

2 linked monosaccharides form a disaccharide

A polymer of many monosaccharides is a

polysaccharide


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Carbohydrates are important energy sources for

most organisms Most small carbohydrates are water-soluble due

to the polar OH functional group

Glucose (C6H

12O

6) is the most common

monosaccharide in living organisms

Sugar dissolving in water

hydrogen

bond

hydroxyl

group

water


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Glucose (C6H12O6)


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There are several monosaccharides with slightly

different structures

The basic monosaccharide structure is:

A backbone of 37 carbon atoms

Most of the carbon atoms have both a hydrogen (-H)

and an hydroxyl group (-OH) attached to them

Most carbohydrates have the approximate chemical

formula (CH2O)nwhere n is the number of carbons in

the backbone

When dissolved in the cytoplasmic fluid of a cell, the

carbon backbone usually forms a ring

Example of monosaccharides

Glucose (C6H12O6): the most common


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Additional monosaccharides are:

Fructose (fruit sugar found in fruits, corn syrup,and honey)

Galactose (milk sugar found in lactose)

Ribose and deoxyribose (found in RNA and

DNA, respectively)


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Monosaccharides

Fig. 3-5

galactosefructose

6

5

4

32

12

34

5

1

6


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Ribose Sugars

Fig. 3-6

ribose deoxyribose

Note missing

oxygen atom


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The fate of monosaccharides inside a cell is:

Some are broken down to free their chemicalenergy

cellular respiration

Some are linked together by dehydration

synthesis

energy storage


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Disaccharides consist of 2 monosaccharides

linked by dehydration synthesis They are used for short-term energy storage

When energy is required, they are broken apart

by hydrolysis into their monosaccharide subunits

glucose fructose sucrose

dehydrationsynthesis


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Examples of disaccharides include:

Sucrose(table sugar) = glucose + fructose Lactose(milk sugar) = glucose + galactose

Maltose(malt sugar) = glucose + glucose


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Polysaccharides are chains of simple sugars

Storage polysaccharides include:

Starch, an energy-storage molecule in plants, formedin roots and seeds

Glycogen,an energy-storage molecule in animals,found in the liver and muscles

Both starch and glycogen are polymers of glucosemolecules


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Starch is an Energy-Storing Plant Polysaccharide

(b) A starch molecule

(a) Potato cells

(c) Detail of a starch molecule

starch grains

Fig. 3-8


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Many organisms use polysaccharides as a structural

material Cellulose(a polymer of glucose) is one of the most

important structural polysaccharides

found in the cell walls of plants

indigestible for most animals due to the orientation ofthe bonds between glucose molecules


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Cellulose Structure and Function

Fig. 3-9


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Chitin(a polymer of modified glucose units) isfound in:

The outer coverings of insects, crabs, and

spiders

The cell walls of many fungi


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What Are Lipids?

Lipidsare a diverse group of molecules that

contain regions composed almost entirely of

hydrogen and carbon

All lipids contain large chains of nonpolar

hydrocarbons

Most lipids are therefore hydrophobic and waterinsoluble


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What Are Lipids?

Lipids are diverse in structure and serve a

variety of functions

They are used for energy storage

They form waterproof coverings on plant and

animal bodies

They serve as the primary component of cellular

membranes

Some are hormones


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What Are Lipids?

Lipids are classified into 3 major groups

1. Oils, fats, and waxes2. Phospholipids

3. Steroids containing rings of carbon, hydrogen,

and oxygen

A i i ?


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What Are Lipids?

1. Oils, fats, and waxes

Oils, fats, and waxes are made of 1 or morefatty acidsubunits

Fatsand oils

Are used primarily as energy-storage

molecules, containing 2X as many caloriesper gram as carbohydrates and proteins

Are formed by dehydration synthesis 3 fatty acids + glyceroltriglyceride

S h i f T i l id


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glycerol fatty acids

triglyceride

Synthesis of a Triglyceride

Fig. 3-12

Wh t A Li id ?


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What Are Lipids?

Oils, fats, and waxes

Fats that are solid at room temperature aresaturated(the carbon chain has as many

hydrogen atoms as possible, and mostly or all C-

C bonds); for example, beef fat

Wh t A Li id ?


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What Are Lipids?


Fats that are liquid at room temperature areunsaturated(with fewer hydrogen atoms, and

many C=C bonds); for example, corn oil

Unsaturated trans fats have been linked to

heart disease

Wh t A Li id ?


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What Are Lipids?


Waxes are highly saturated and solid at room temperature

Waxes form waterproof coatings such as on:

Leaves and stems in plants

Fur in mammals

Insect exoskeletons Waxes are also used to build honeycomb structures

Wh t A Li id ?


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What Are Lipids?

Phospholipids

Phospholipids consist of 2 fatty acids + glycerol +a short polar functional group

These form plasma membranes around all cells

They have hydrophobic and hydrophilic portions

The polar functional groups form the head

and are water-soluble

The nonpolar fatty acids form the tails and

are water insoluble

Ph h li id


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Phospholipids

Fig. 3-14

polar head glycerolbackbone

phosphategroup

variablefunctional

group

(hydrophilic) (hydrophobic)

fatty acid tails

Wh t A Li id ?


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What Are Lipids?

Steroids

Steroids are composed of 4 carbon rings fusedtogether with various functional groups

protruding from them

Examples of steroids include:

Cholesterol

Found in the membranes of animal cells

Male and female sex hormones

Steroids


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Steroids

Fig. 3-15

What Are Proteins?


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What Are Proteins?

Functions of proteins

Proteinshave a variety of functionsEnzymes are proteins that promote chemical

reactions

Structural proteins (e.g., elastin) provide

support

What Are Proteins?


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What Are Proteins?

Proteins are formed from chains of amino acids joined

by peptide bonds

All amino acids have a similar structure

All contain amino and carboxyl groups

All have a variable R group

Some R groups are hydrophobic

Some are hydrophilic

Cysteine R groups can form disulfide bridges

amino

group

hydrogen

variable

group

carboxylic

acid group

Amino Acid Diversity


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glutamic acid (glu) aspartic acid (asp)(a) Hydrophilic functional groups (b) Hydrophobic functional groups

(c) Sulfur-containing

functional group

leucine (leu)phenylalanine (phe)

cysteine (cys)

Amino Acid Diversity

Fig. 3-18

What Are Proteins?


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What Are Proteins?

Amino acids are joined to form chains by dehydration

synthesis

An amino group reacts with a carboxyl group, and wateris lost

The covalent bond resulting after the water is lost is a

peptide bond,and the resulting chain of 2 amino acids is

called a peptide Long chains of amino acids are known as polypeptides,

or just proteins

The sequence of amino acids in a protein dictates its

function

What Are Proteins?


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What Are Proteins?

Proteins exhibit up to 4 levels of structure Primary structureis the sequence of amino

acids linked together in a protein Secondary structurecan be a helix,or a

pleated sheet

Tertiary structurerefers to complex foldings of

the protein chain held together by disulfidebridges, hydrophobic/hydrophilic interactions,and other bonds

Quaternary structureoccurs where multipleprotein chains are linked together

The Four Levels of Protein Structure


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The Four Levels of Protein Structure

(a) Primary structure:The sequence of amino acidslinked by peptide bonds

(c) Tertiary structure:Folding of the helix resultsfrom hydrogen bonds withsurrounding water moleculesand disulfide bridges betweencysteine amino acids

(d) Quaternary structure:Individual polypeptides arelinked to one another byhydrogen bonds or disulfidebridges

(b) Secondary structure:Usually maintained byhydrogen bonds, whichshape this helix

helix

hydrogenbond

heme group

leu

val

lys

lys

gly

his

ala

lys

val

lys

pro

The Pleated Sheet: An Example of Secondary Structure


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The Pleated Sheet: An Example of Secondary Structure

Fig. 3-21pleated sheet

hydrogen

bond

What Are Proteins?


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What Are Proteins?

The functions of proteins are linked to their

3-dimensional structures

Precise positioning of amino acid R groups

leads to bonds that determine secondary

and tertiary structure

Disruption of secondary and tertiary bondsleads to denaturedproteins and loss of

function

Hair is Composed of the Protein Keratin


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single hair

enlargement

of single hair

microfibril

protofibril

helix of

single keratin

molecule

disulfide bonds in

straight hair

hydrogen bonds




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Hair is composed of helical keratin proteins

intertwined and held together by disulfide bonds.

Hair straightens out when wet because the H-

bonds that create the helical structure are broken

and replaced by H-bonds between the amino acidsand the H2O molecules between them. The protein

becomes denatured and the helices collapse.



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Curly hair is curly due to the specific sequence of amino

acids. The disulfide bonds within and between the individual

keratin molecules are located such that the helices arekinked, forming curls.

When curly hair is stretched out, the H-bonds that hold the

helical structure together are broken, thus straightening the

hair. The covalent S-S bonds are distorted but not broken.

What Are Nucleic Acids?


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Nucleotidesact as energy carriers and

intracellular messengers

Nucleotides are the monomers of nucleic acid

chains

All nucleotides are made of 3 parts:

Phosphate group

5-carbon sugar

Nitrogen-containing base

Adenosine triphosphate (ATP)is a ribosenucleotide with 3 phosphate functional groups

Deoxyribose Nucleotide


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sugar

phosphate

base

Deoxyribose Nucleotide

Fig. 3-22

The Energy-Carrier Molecule Adenosine Triphosphate


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The Energy Carrier Molecule Adenosine Triphosphate

(ATP)

Fig. 3-23



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DNA and RNA, the molecules of heredity, are

nucleic acids

There are 2 types of polymers of nucleic acids

DNA(deoxyribonucleic acid)is found in

chromosomes and carries genetic information

needed for protein constructionRNA (ribonucleic acid)makes copies of DNA

and is used directly in the synthesis of

proteins



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Each DNA molecule

consists of 2 chains of

nucleotides that forma double helix linked

by hydrogen bonds

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021113 Chapter3 Revised RNA