cmb lect 2 2011 colour slides.pdf

8/14/2019 CMB Lect 2 2011 colour slides.pdf

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A question from a previous year

The electron micrograph above represents a cross-section of a:1. chloroplast.2. mitochondrion.

BIOSCI 101: Cellular and Molecular Biology

3. eukaryotic flagellum.4. Golgi body.5. ribosome.

LECTURE 2

The Chemical Components of


e s


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Chemical composition of cells

.-70% of the weight of bacteria and most cellsis water- the dry residue contains 50% C, 10% N,15% H, 20% O and 5% other includingS (protein) and P (nucleic acid)


Cell fractionation

acid.

- the acid soluble fraction (20%) containssmall molecules.- the acid-insoluble fraction (80%) containslarge molecules (macromolecules) which can


for non-polar solvents.


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Fractionation of a cell homogenate


Polymer assembly and degradation

Princi les of ol mer assembl and de radation.- polymers are large molecules made of manyidentical or similar building blocks (monomericsubunits).- the monomers are joined via condensationreactions in which a molecule of water is lost(one monomer provides the -H and the other the


- .- polymers are disassembled by the reverseprocess (hydrolysis). Bonds between monomersare broken by the addition of water molecules.


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Campbell 5.2(a) Dehydration reaction: synt hesizing a polymer

Short polymer Unlinked monomer

Dehydration removesa water molecule,forming a new bond.

1 2 3

and degradation

Longer polymer

(b) Hydrolys is: breaking dow n a polymer

1

1

2 3 4

2 3 4


Hydrolysis addsa water molecule,breaking a bond.

1 2 3

Macromolecules a) Lipids- soluble in non-polar organic solvents such as

- used as energy sources, structural molecules(membranes), hormones etc.

i) Fats- formed by the combination of two typesof compounds - glycerol (an alcohol) andfatt acids


- largely hydrophobic (water-fearing) andtherefore water-insoluble.- major use as storage material (6Xenergy of glycogen)


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Synthesis of a fat molecule

Fatty acid(in this case, palmitic acid )

BIOSCI 101: Cellular and Molecular BiologyCampbell 5.10a

(a) One of three dehydration reactions in the synthesis of a fat

Structure of a fat moleculeEster linkage

BIOSCI 101: Cellular and Molecular BiologyCampbell 5.10b

(b) Fat molecule (triacylgl ycerol)


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Macromolecules (contd) a) Lipids (contd)

ii Phos holi ids- same general structure as fats except thatone fatty acid is replaced by a phosphate -linked group- amphipathic ie hydrophilic (water-loving)head and hydrophobic tail- in water, they self-assemble into aggregates


a s e e r y rop o c por ons romthe aqueous environment - micelles andbilayers- important molecules in the structure ofmembranes

Structure of a phospholipid

BIOSCI 101: Cellular and Molecular BiologyCampbell 5.12


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The phospholipid bilayer


Macromolecules (contd)

- composed of sugars linked by glycosidicbonds

- monosaccharides - 1 sugar molecule eg glucose,fructose, ribose

- disaccharides - 2 sugar molecules eg sucrose,


ac ose- polysaccharides - many sugar molecules linked

together into chains


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Monosaccharides and disaccharides


Functions of polysaccharidesPolysaccharides may be used:-- as energy stores eg glycogen is stored inmuscles; starch is an important storage materialin plants- as structural material eg cellulose in plants (apolymer of glucose); chitin in exoskeletons ofcrustacea and insects- carbohydrate residues can also be joined to


proteins or lipids (glycoproteins and glycolipids).


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Stora epolysaccharides


Storage

(contd)



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Structural polysaccharides (1)


Structural polysaccharides (2)



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c) Proteins

- all proteins consist of the same 20 amino acidsin different molar proportions- amino acids are linked by peptide bonds, each


chain = a polypeptide

Macromolecules (contd) c) Proteins (contd)

- amino acids have 4 groups bonded to a centralC atom called the -carbon:

-a carboxyl group COOH-an amino group NH 2-a hydrogen atom H-a side chain which is different


for each amino acid R- charged and polar amino acids arehydrophilic, nonpolar amino acids tend to behydrophobic


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- in making the peptide chain, the charged aminoand carboxyl groups are all used to form peptidebonds (except for those at the C- and N-termini)- the backbone is informationally uninteresting.


e s e groups groups prov e sense aninformation.- diverse range of functions (see Lecture 5)

Amino acid structures (1)Nonpolar side chains; hydroph obicSide chain

Glycine(Gly or G)

Alan in e(Ala or A)

Valine(Val or V)

Leucine(Leu or L)

Isoleucine(I le or I )


Methionine(Met or M)

Phenylalanine(Phe or F)

Tryptophan(Trp or W)

Proline(Pro or P)


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Amino acid structures (2)

Polar side chains; hydrophi lic

Serine(Ser or S)

Threonine(Thr or T)

Cysteine(Cys or C)


Tyrosine(Tyr o r Y)

Asparagi ne(Asn or N)

Glutamine(Gln or Q)

Amino acid structures (3)

Electrically charged side chains; h ydrophilic

Acidic (n egat ivel y charged)

BIOSCI 101: Cellular and Molecular BiologyCampbell 5.16c

Aspart ic acid(Asp or D)

Glutamic acid(Glu or E)

Lysine(Lys or K)

Arg in in e(Arg or R)

Histidine(His or H)


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Making apolypeptide

chain

Peptide bond

New p eptidebond forming

Sidechains


Back-bone

Ami no end(N-terminus)

Peptidebond

Carboxyl end(C-terminus)

Macromolecules (contd) d) Nucleic Acids (RNA and DNA)

- consist of long chains of nucleotides whichthemselves consist of three subunits- a phosphate group, a 5-carbon sugar and anitrogenous base- the nucleotides are joined by phosphodiesterbonds


- n e ac one con a ns e sugar r osewhereas in DNA the backbone contains the sugardeoxyribose


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Macromolecules (contd) d Nucleic Acids contd

- the nitrogenous bases can be purines (A & G) orpyrimidines (C & T or U)- the informational interest of the moleculecomes from the bases bonded to the sugar-phosphate backbone


- all informational processes in the cell involveDNA and RNA. Nucleotides have other functionsin cells eg storage of chemical energy in ATP,intracellular signalling cAMP.

Components of nucleic acidsSugar-phosphate backbone5 end

5 C

3 C

Nitrogenous basesPyrimidines

5 C

3 C (b) Nucleotide

Phosphategroup Sugar

(pentose)

Nucleoside

Nitrogenousbase

5 C

3 C

1 C

Cytosine (C) Thymine (T, in DNA) Uracil (U, in RNA)

Adenin e (A) Guanine (G)

Purines


3 end

(a) Polynucleotide, or nucleic acid

Sugars

Deoxyribose (in DNA) Ribose (in RNA)

(c) Nucleoside components


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The DNA doublehelix3.4 nm

C

C

C

C

G

G

G

G

T A

1 nm

C

C

C

C

G

G

G

G

T

T

A

A


Campbell 16.7a0.34 nm

C G

T

T

T

A

A

A

Now for a quick test..

1. They can both be digested by humans2. They are both polymers of glucose.3. They are both structural components of plant cell walls.4. They are geometric isomers of each other.5. They are both used for energy storage in plants.


cmb lect 2 2011 colour slides.pdf

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