Biology 1020 lecture 5 Biological Molecules B
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Proteins do work in cells
- 3D folded and coiled molecules - structure fits function
- 50% of the dry mass of cells
- 1+ polypeptides
Functions of Proteins
- Provide support (keratin and collagen)
- Move cells, organelles ( muscles - actin and myosin)
- Assist chemical reactions (enzymes)
- Store amino acids (e.g. ovalbumin)
- Protect against disease (antibodies)
- Co-ordinate activities (hormones)
- Transport materials between cells (hemoglobin)
- Allow cells to detect and respond to stimuli-receptors on cell surfaces
- polymer: polypeptide
- monomer: amino acids
- ** 50-34000 amino acids long peptide
Amino acid structure
- central alpha carbon
- carboxyl and amino group
- side chain/variable groups - R group
- grouped based on properties of R groups at pH 7.2
- - polar
- - uncharged
Amino Acids are catergorized characteristics
Amino Acids (ex. Aspartic or Glutamic acid): They have a carboxyl group on their side chain that can donate a H+
Amino Bases (ex. Lysine, Arginine, Histidine): They have a nitrogen group on their side chain that can accept H+
Non-Polar Amino Acids (ex. Tryptophan and Glycine): They have lots of hydrocarbon bonds that are non-polar on their side chains.
Polar Amino Acids (ex. Serine): They have hydroxides, disulfide, and/or NH2-C=O group on side chain.
Amino acids are held together in polypeptides by peptide bonds formed via a dehydration reaction between the carboxyl and the nitrogen groups on the main backbone of the amino acid.
- Order and properties of amino acids determine shape
- Activity/function in a particular region (action site of protein)
- Other molecules bind/fit into a specific space
Protein Shape #2
- Starts to fold into shape as it is synthesized
- Physical interactions assist folding
- aqueous environment
- e.g. non-polar amino acids shielded from water
- parts of the chain brought close together
Levels of structure of a protein
- Quaternary (most folded)
Protein Primary Structure
- Unique sequence of amino acids
- Determined by the gene sequence
- (Just the sequence of "beads" on a necklace. Amino acids).
Protein Secondary Structure #1
- Coils or folds in polypeptide
- Hydrogen bonds between different parts of polypeptide backbone. O-ve H+ve
- properties determined by mix of structure
Protein secondary structure #2
α helix: Proteins rich in alpha helical structures tend to be fibrous and strong.
β pleated sheet: Proteins rich in beta sheets tend to stretch and recoil.
Protein Tertiary Structure
- Hydrophobic amino acids shield from water
- R groups close together for H bonding
- Disulfide bridges
- * Covalent bond. -S-S- cysteines
Protein Quaternary Structure
- 2+ polypeptide chains form one molecule.
- Can be Globular (e.g. hemoglobin, 2 beta and 2 alpha chains), or Fibrous (e.g. collagen - 3 polypeptides coiled)
Protein structure affected by...
- Solute Concentration
Loss of Protein Structure
- Protein is denatured when it has lost proper 3D structure and loses function
- Denatured proteins can aggregate in harmful ways in cells.
- In some cases, the denatured protein can be renatured to a normal protein.
Protein (re)folding: Chaperonins
- Stressors such as heat can cause a protein to unfold
- Chaperonins assist the proper folding/refolding of other proteins.
- Chaperonin consists of a cap and a hollow cylinder
Small changes to protein structure affect function: Sickle cell hemoglobin
- Inherited blood disorder, Sickle-cell disease
- Single amino acid substitution in hemoglobin
- Glutamine-polar becomes Valine-non polar
- changes primary level to quarternary level
- Infectious proteins
- * Mammals
- * Fungi
- Abnormally folded, Not denatured by most denaturants such as heat, radiation, etc.
- Cause normal proteins to lose their structure
- - infectious
- DNA - Deoxyribonucleic Acid
- RNA - Ribonucleic Acid
Passing of information
- Synthesis of mRNA in the nucleus (transcription)
- Movement of mRNA into cytoplasm via nuclear pore
- Goes to ribosome. Synthesis of protein (translation)
Nucleic Acid: Monomers
Called Nucleotides: Nucleoside (nitrogenous base and pentose sugar) and phosphate.
- Single ringed
- Double ringed
- Sugar-phosphate backbone
- - Covalent bond
- - OH on #3 carbon of one sugar
- - Phosphate on #5 carbon
- Nitrogenous bases as appendages
- Forms helix structures
DNA double helix
- 2 polynucleotide spiral around an axis
- Backbones run in opposite directions
- => anti-paraellel
- 5'--> 3'
- 3'--> 5'
- H bonds between. Nitrogenous bases: A-T and G-C
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