Summary

1. Eukaryotic cells keep genetic information in DNAenclosed in cell nucleus and mitochondria and chloroplasts (plants);

2. The genomes of several model organisms are completelysequenced;

3. Long DNA molecules are efficiently packed in chromosomes;4. Cell nucleus is a highly organized structure;5. Different sets of genes are expressed in different tissues;6. Epigenetic regulation of gene expression.

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More about cell nucleus later…

Lecture 2Cell chemistry and

biosynthesis

1

70% of a cell’s weight is waterthe most abundant substance in cells

Life on Earth began in the ocean

Hydrogen bond link water molecules together so that water is a liquid form at room temperature (RT)

2

Cells contain four major families of small organic molecules

They can also exist in monomers and be broken downin metabolic pathways

3

Glucose monomer 4

Monosaccharide todisaccharide

5

Polysaccharide-Glycogen

6

Fatty acids are usually covalently linked other molecules by theircarboxyl group in a cell

7

Some fatty acids contain double bonds between carbons

Essential structureof a cell!!!

9

Lipids: a loosely defined collection of biological molecules which are insoluble in water while being soluble in fat andorganic solvents such as benzene. They either contain long hydrocarbon chains, as in the fatty acids and isoprenes,or multiple linked aromatic rings,such as in the steroids.Examples: fatty acids and their derivative such as triacylglycerols

Phospholipids: amphipathic

Lipids and phospholipids8

Amino acids and proteins 10

Nucleotides and nucleic acids 11

Macromolecules are abundant in cells12

Noncovalent bonds specify both the precise shape of a macromolecule and its binding to other molecules

13

Metabolic pathways andtheir interconnections

500 reactions

14

Two opposing streamsof chemical reactions

15

Second law of thermodynamics

Greaterentropy

16

G= Go+0.616ln[B]/[A]

A B

17

GPositive--noNegative--yes

A peptide bond

18

19

The 20 amino acids found in proteins20

Three types of noncovalent bonds driving protein folding21

Polar amino acid side chains gather on the outside22

Secondary structure: helix

Formed by hydrogen bonds in the polypeptide backbone

23

Secondary structure: sheet

Formed by hydrogen bonds in the polypeptide backbone

24

Coiled-coil: from hydrophobic helices

25

Protein domains (40-350 aa): modular units26

A protein “dimer”27

A “tetramer”

28

A tetramer of two different subunits29

Sizes and shapes of domains and proteins 30

Actin polymers:important componentsof cytoskeleton!

31

Self-assembly of a macromolecule aggregate32First example

Bacterial ribosome:55 proteins, 3 rRNAs

Proteins don’t work alone: Protein-protein interactionsbetween functional groups of proteins--challenges in “post-genome” era

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Summary34

1. Cells follow rules of chemistry;2. Water is the most abundant substance

proteins constitutes most of a cell’s dry mass;3. Four major classes of small organic molecules

make macromolecules;4. Living cells undergo metabolism;5. A reaction will happen if it can result in lower

free energy in the system;6. Proteins and protein complexes execute almost

all cell functions.