222 Cell Biology1 الحمد لله رب العالمين الذي هدانا لهذا وما كنا لنهتدي لولا أن هدانا الله والصلاة والسلام على أشرف الأنبياء والمرسلين العالمين

222 Cell Biology2 Lecture 3

222 Cell Biology3 Cellulose Plant Cell Walls It is a polymer of glucose that forms Plant Cell Walls cellulose is the most abundant organic molecule on Earth

222 Cell Biology4 Chitin Polysaccharide Is a Polysaccharide used by insects and crustaceans to build an exoskeleton cell wall of fungi Found in cell wall of fungi

222 Cell Biology5 Hyaluronic acid connective tissues Found in connective tissues 1,3 glycosidic bond 1,4 glycosidic bond

222 Cell Biology6 Inulin Found in some plantes, formed of fructose units (b 1,2 glycosidic bond)

222 Cell Biology7 Glycogen storage polysaccharide glucose Is a storage polysaccharide composed of glucose, which is hydrolyzed by animals when glucose is needed Highly branched molecules

222 Cell Biology8 Starch Is a storage polysaccharide glucose monomers composed of glucose monomers plants and found in plants Starch helix may be unbranched or branched

222 Cell Biology9 Other polysaccharides Mannose units Formed of Mannose units Found in Yeast (branched) and in Some plantes ( non-branched)

222 Cell Biology10 Paramylum Homopolsaccharides, found in Euglina

222 Cell Biology11 Dextrin Branched polysaccharides, produced by some bacteria

222 Cell Biology12 Complex polysaccharides Polysaccharides can combine with other c cc classes of macromolecules to form complex polysaccharides: GGGGlycoproteins: polysaccharides + proteins GGGGlycolipids: polysaccharides + lipids CCCCellular functions Cell-surface receptor molecules; typically reside on external surfaces of the membrane Glycolipids important in cell walls of gram-negative bacteria

222 Cell Biology13 PROTEINS 20 amino acid Are a polymer built from various combinations of 20 amino acid Monomers Are the most abundant macromolecules in cells found throughout cell structural and enzymatic roles Have an important structural and enzymatic roles Transmit information between cells (e.g : protein hormones) Provide a defense against infection (e.g antibodies) Account for more than 50% of the dry mass of cells. Proteins divided into two groups based on its function in the cells: Structural proteins : Integral parts of cellular structures (Fibrous proteins (Collagen), cartilage, skin and bone (keratin.(tubulin, actin like protiens, microtubules and,Microfilaments Dynamic proteins : Catalytic proteins; catalysts for chemical reactions, cell metabolism (hormones, insulin, erthrproetin and thyroxine, hemoglobin- hemocyanin-myoglobin

222 Cell Biology14 PROTEINS Proteins can be divided into three main classes, which correlate with typical tertiary structures: 1- Globular proteins: Almost all are soluble and many are enzymes. 2- Fibrous proteins: Fibrous proteins are often structural, such as collagen, the major component of connective tissue, or keratin, the protein component of hair and nails Membrane proteins: Membrane proteins often serve as receptors or provide channels for polar or charged molecules to pass through the cell membrane.

222 Cell Biology15 Amino Acids  Most consist of carbon, hydrogen, oxygen, and nitrogen; 2 of 22 contain sulfur, 1 contains selenium  All contain two important functional groups Carboxylic acid group (-COOH) Carboxylic acid group (-COOH) Amino group (-NH 2 ) Amino group (-NH 2 ) Peptide bonds.  Amino acid monomers held together by covalent bonds Peptide bonds.  Polypeptides: thousands or millions of amino acids Have two distinct ends: one terminating in an  amino group (the amino- or N- terminus) and the other is an  carboxylic group (carboxyl or C-terminus)  Protein consists of a specific amino acid sequence  The amino acid sequence of protein determines its three dimensional structure and its chemical reactivity.  Side chains of amino acids impart its chemical properties

222 Cell Biology16

222 Cell Biology17 Peptide bond Peptide Bonds The amino acids in a polypeptide chain are linked by Peptide Bonds This bond links the carboxyl group of one amino acid to the amino group of the next amino acid

222 Cell Biology18 Conjugated proteins A conjugated protein is a protein that functions in interaction with other chemical groups Nucleoproteins: o Nucleoproteins: chromosome Chromoprotein: o Chromoprotein: haemoglobin Phosphproteins: o Phosphproteins: found in milk Glycoproteins : o Glycoproteins : contain oligosaccharide chains covalently attached to their polypeptide side-chains, they play a role in cell-cell interactions o Lipioproteins: o Lipioproteins: enzymes, transporters

222 Cell Biology19 Levels of protein structure Protein can have four levels of structure: Protein can have four levels of structure: 1- Primary structure 2- Secondary structure 3-Tertiary structure 4-Quaternary structure Primary structure Primary structure Primary structure: sequence of amino acids in a polypeptide -The correct amino acid sequence is determined by the cell’s genetic information -The slightest change in this sequence affects the protein’s ability to function -Sickle cell disease is manifested by an inability of hemoglobin in red blood cells to carry oxygen, the primary function of hemoglobin. This blood disorder is the result of change in a single amino acid

222 Cell Biology20 Four levels of protein structure Four Levels of Protein Structure Amino acids Primary structure Alpha helix Hydrogen bond Secondary structure Pleated sheet Polypeptide (single subunit of transthyretin) Tertiary structure

222 Cell Biology21 2- Secondary structure Secondary structure: Secondary structure: the regular arrangement of amino acids within localized regions of the polypeptide Folds in polypeptide that form a more stable structure, often involving hydrogen bonding between R groups There are two types of secondary structure: (α-helix)  Helical structure called an alpha helix (α-helix) (region of polypeptide chain coils around itself (β sheet):  Pleated sheet (β sheet): two parts of polypeptide chain lie side by side with hydrogen bonds between them.

222 Cell Biology22 Tertiary structure Tertiary structure: Tertiary structure: additional folding of polypeptide to result in greater stability and unique three-dimensional shape  Forms exposed regions or grooves in the molecule that are important for binding other molecules  Disulfide bonds:  Disulfide bonds: bonds between -SH groups from two different amino acids Domains In most proteins combination of alpha helix and beta sheets connected by loop regions of polypeptide chain, fold into compact globular structures called Domains (the basic unit of tertially structure)

222 Cell Biology23 Quaternary structure Quaternary structure: Quaternary structure: occurs in proteins composed of two or more polypeptides  Subunit:  Subunit: each polypeptide in the protein, held together by either/both covalent and noncovalent linkages  Homodimer:  Homodimer: protein containing two identical subunits  Heterodimer:  Heterodimer: protein containing two nonidentical subunits

222 Cell Biology24 وفقنا الله وإياكم لما فيه خير أمتنا الإسلامية