Amino acids. Side chain. -Carbon atom. Carboxyl group. Amino group

Transcription

1 PROTEINS

2 Amino acids Side chain -Carbon atom Amino group Carboxyl group

3 Amino acids

4 Primary structure Amino acid monomers Peptide bond

5 Peptide bond Amino group Carboxyl group Peptide bond N-terminal ( + H 3 N) C-terminal (COO )

6 Secondary structures -helix -sheet Hydrogen bond Hydrogen bond

7 Tertiary and quaternary structures Tertiary structure -sheet Quaternary structure Subunit 1 Subunit 2 Hydrogen bond -helix Disulphide bridge Subunit 3 Subunit 4

8 Disulphide bridge cysteine molecules side chains disulphide bridge

9 Denaturation Native protein Denatured protein

10 The subunits of hemoglobin -subunits red blood cells hem group -subunits

11 Macromolecular assemblies Transcription pre-initiation complex virus capsid

12 Types of proteins

13 ENZYMES

14 The First Law of Thermodynamics The laws of thermodynamics Energy before Energy transformation Energy after The Second Law of Thermodynamics Energy before Energy transformation Usable energy after (free energy) Unusable energy after Free energy Energy transformations Unusable energy after Entropy

15 Exergonic reaction Reactants Amount of energy released Products Endergonic reaction Products Amount of energy required Reactants

16 Activation energy Energy barrier Transition state Reactants (stable) E a G Products Stable state Less stable state (transition state)

17 Enzyme and substrate Active site Product Enzyme Enzyme substrate complex Enzyme

18 Enzymes lower the energy barrier E a Uncatalyzed reaction E a Reactants Catalyzed reaction G Products

19 Life at the Active Site Enzymes orient substrate molecules, bringing together the atoms that will bond Citrate synthase Lysozyme Enzymes can stretch the bonds in substrate molecules, making them unstable Chymotrypsin Enzymes can temporarily add chemical groups to substrates

20 Some enzymes change shape when substrate binds to them Empty active site Glucose substrate

21 Some examples of nonprotein partners of enzymes

22 Metabolic Pathways Metabolism of Cofactors and Vitamins Nucleotide Metabolism Carbohydrate Metabolism Lipid Metabolism Metabolism of Other Amino Acids Amino Acid Metabolism ATP production Metabolism of Other Substances

23 Irreversible Inhibition Active site DIPF Trypsin Hydrogen fluoride

24 Competitive inhibitor Competitive inhibition Active site Reversible Inhibition Substrate Noncompetitive inhibition Substrate Active site Noncompetitive inhibitor

25 Allosteric Regulation of Enzymes Inactive form Catalytic subunit Active form Active site Inhibitor site Regulatory subunits Substrate Activator site Allosteric inhibitor Allosteric activator No product formation Product formation

26 Allosteric Regulation of Enzymes Catalytic subunit INACTIVE FORM ACTIVE FORM Active site Inhibitor site Regulatory subunits Activator site The enzyme switches back and forth between the two forms. They are in equilibrium

27 Allosteric Regulation of Enzymes INACTIVE FORM When the enzyme is in the inactive form, it cannot accept substrate.

28 Allosteric Regulation of Enzymes INACTIVE FORM Allosteric inhibitor Binding of an inhibitor makes it less likely that the active form will occur.

29 Allosteric Regulation of Enzymes ACTIVE FORM Substrate When the enzyme is in the active form, it can accept substrate.

30 Allosteric Regulation of Enzymes ACTIVE FORM Substrate Allosteric activator Binding of an activator makes it more likely that the active form will occur.

31 Allosteric Regulation of Enzymes INACTIVE FORM ACTIVE FORM No product formation Product formation

32 Translation

33

34 12.8 Transfer RNA

35 12.9 Charging a trna Molecule (Part 1)

36 12.9 Charging a trna Molecule (Part 2)

37 12.10 Ribosome Structure

38 The Initiation of Translation

39 The Initiation of Translation

40 The Elongation of Translation

41 The Elongation of Translation

42 The Termination of Translation

43 The Termination of Translation

44 The Termination of Translation

45 Polysome

46 Post-translational regulation

47 Protein degradation proteasome Causes of degradation: - aberrant structure - Optimal life time - No need any more - Starvation for amino acids Life time: short-lived proteins: e.g. steroid receptor; long-lived proteins: pl. eye lens proteins - Amino acids at the N-terminus is correlated with: 1. stability 2. rate of ubiquitin binding - Arg, Lys, Phe, Leu, Trp 1/2 life: 3 min - Cys, Ala, Ser, Thr, Gly, Val, Pro, Met 1/2 life: 20 hrs Ubiquitin (a peptide composed of 76 amino acids) binds to proteins and identify them for degradation by proteolytic enzymes in proteasomes

48 Protein degradation

49 Protein modification 16. precursor peptide peptide variants 1. Proteolytic cleavage - Various peptides from a precursor molecule (e.g. neuropeptides) - Cleavage of inhibitory peptide (e.g. digestive enzymes) 2. Glycosylation: transport (control the final location of proteins) I 3. Phosphorylation: activation - inactivation 4. Methylation acetylation: histone regulation protein inactive kinase phosphatase protein active P N-acetilgluckosamine mannose glucose protein Carbohydrate group glycosylation: addition of glycosyl group