Four Levels of Protein Structure

Size: px
Start display at page:

Download "Four Levels of Protein Structure"

Transcription

1 Primary structure (1 ) Four Levels of Protein Structure sequence of amino acids Secondary structure (2 ) ini8al folding alpha(α) helices or beta(β) sheets in the polypep8de chain Ter8ary structure (3 ) interac8ons among side chains (R groups) combina8ons of α- helices and β- sheets Quaternary structure (4 ) protein consists of mul$ple polypep8de chains

2 Four Levels of Protein Structure Primary structure Sequence of amino acids Dictated by sequence of nucleo8des in DNA Codon set of three nucleo8des code for a specific amino acid

3 secondary structure Four Levels of Protein Structure result from hydrogen bonds between backbones of amino acids Not R groups α helices Secondary Structure coiled H- bond between every fourth amino acid amino acid subunits β pleated sheet α kera8n - hair β pleated sheet α helix Accordian folds Amyloid plaques of Alzheimers

4 Four Levels of Protein Structure Ter8ary structure Combina8ons of helices and pleated sheets determined by interac8ons between R groups, rather than interac8ons between backbone cons8tuents covalent bonds hydrogen bonds ionic bonds hydrophobic interac8ons van der Waals interac8ons Strong covalent bonds called disulfide bridges may reinforce the protein s structure

5 Four Levels of Protein Structure Quaternary structure results when two or more polypep8de chains form one macromolecule Collagen fibrous protein consis8ng of three polypep8des coiled like a rope Hemoglobin globular protein with four polypep8des: two alpha and two beta chains Tertiary Structure Quaternary Structure Polypeptide chain β Chains Iron Heme Collagen α Chains Hemoglobin

6 Fig Primary Structure Secondary Structure Tertiary Structure Quaternary Structure β pleated sheet + H 3 N Amino end Examples of amino acid subunits α helix

7 What Determines Protein Structure? In addi8on to primary structure physical and chemical condi8ons can affect structure ph salt concentra8on Temperature other environmental factors can cause a protein to unravel Denaturation Denatura8on loss of a protein s na8ve Normal protein Renaturation Denatured protein structure Now biologically inac8ve

8 Protein Folding in the Cell It is hard to predict a protein s 3D structure from its primary structure Sequences of 1.2 million proteins known Only 8, D shapes known Most proteins probably go through several states on their way to a stable structure Chaperonins protein molecules that assist the proper folding of other proteins Cap Polypeptide Correctly folded protein Hollow cylinder Chaperonin (fully assembled) Steps of Chaperonin Action: 1 An unfolded polypeptide enters the cylinder from one end. 2 The cap attaches, causing the 3 cylinder to change shape in such a way that it creates a hydrophilic environment for the folding of the polypeptide. The cap comes off, and the properly folded protein is released.

9 Nucleic Acids Store and transfer gene8c informa8on Gene unit of inheritance codes for the amino acid sequence of a polypep8de Genes are made of DNA, a nucleic acid

10 The Roles of Nucleic Acids Two types of nucleic acids: Deoxyribonucleic acid (DNA) Ribonucleic acid (RNA) DNA provides direc8ons for its own replica8on directs synthesis of messenger RNA (mrna) controls protein synthesis Protein synthesis occurs in ribosomes

11 Fig DNA 1 Synthesis of mrna in the nucleus mrna NUCLEUS CYTOPLASM

12 Fig DNA 1 Synthesis of mrna in the nucleus mrna NUCLEUS CYTOPLASM 2 Movement of mrna into cytoplasm via nuclear pore mrna

13 Fig DNA 1 Synthesis of mrna in the nucleus mrna NUCLEUS CYTOPLASM 2 Movement of mrna into cytoplasm via nuclear pore mrna Ribosome 3 Synthesis of protein Polypeptide Amino acids

14 The Structure of Nucleic Acids Polynucleo8des Nucleic acid polymer Nucleo8de 5ʹ C 5ʹ end Nitrogenous bases Pyrimidines monomers of a polynucleo8de 3ʹ C Nucleoside Nitrogenous base Cytosine (C) Thymine (T, in DNA) Uracil (U, in RNA) Purines a nitrogenous base, a pentose sugar, and a phosphate group 5ʹ C 3ʹ C 3ʹ end (a) Polynucleotide, or nucleic acid Phosphate group (b) Nucleotide Sugar (pentose) Adenine (A) Sugars Guanine (G) Nucleoside por8on of a nucleo8de without the phosphate group Deoxyribose (in DNA) (c) Nucleoside components: sugars Ribose (in RNA)

15 Nucleo8de Monomers Two families of nitrogenous bases: Pyrimidines (cytosine (C), thymine (T), and uracil (U)) single six- membered ring Purines (adenine (A) and guanine (G)) six- membered ring fused to a five- membered ring deoxyribose Sugar in DNA ribose Sugar in RNA

16 Nucleo8de Polymers Nucleo8de Polymers linked together to build a polynucleo8de Adjacent nucleo8des joined by phosphodiester bonds (covalent) between the OH group on the 3ʹ carbon of one nucleo8de and the phosphate on the 5ʹ carbon of the next Create a backbone of sugar- phosphate units with nitrogenous bases as appendages

17 The DNA Double Helix Double helix two polynucleo8des spiraling around an imaginary axis, forming a DNA molecule Nitrogenous bases bond with one another in the middle in An8parallel complementary fashion A- T; C- G two backbones run in opposite 5ʹ 3ʹ direc8ons from each other in the DNA double helix One DNA molecule includes many genes Equals one chromosome

18 You should now be able to: 1. List and describe the four major classes of molecules 2. Describe the forma8on of a glycosidic linkage and dis8nguish between monosaccharides, disaccharides, and polysaccharides 3. Dis8nguish between saturated and unsaturated fats and between cis and trans fat molecules 4. Describe the four levels of protein structure 5. Dis8nguish between the following pairs: pyrimidine and purine, nucleo8de and nucleoside, ribose and deoxyribose, the 5ʹ end and 3ʹ end of a nucleo8de