biochem basicis Flashcards

Question

Write a note on proteins

Answer 1

- Proteins also known as polypeptides - type of macromolecule - Most abundant macromolecule - They are made of amino acids (monomers) - 20 main amino acids (residues) ---> 11 can be synthesised by humans 9 cannot - called essential amino acids (PVT TIM HaLL) STRUCTURE OF AMINO ACIDS: - Has an amino group (NH2) -- In amino acids its prnated to form NH3+ - A carboxyl group (COOH) -- at physiological pH it dissociates into carboxylate ion (COO- ) - R group -- a side chain thats diff for each amino acid - The Carbon atom next to the carboxyl group is known as the ALPHA CARBON - There's also an H atom bound to the alpha carbon - All alpha carbons in in amino acids are chiral centres except in glycine. - Amino acids are linked to each other by PEPTIDE BONDS - Peptide bond formed by a condensation reaction between an alpha carboxyl of one amino acid and the alpha amino of another DIFFERENT FORMS OF AMINO ACIDS: - isomers, stereoisomers, enantiomers - All molecules with one chiral centre have 2 stereoisomers - Amino acids can exist as either L form or D form enantiomers - ALL of the amino acids in humans are in L form enantiomers - D form enantiomers found in peptides in bacterial cell walls and antibiotics AMINO ACIDS ARE CLASSIFIED BASED ON THEIR R GROUPS: - Non-polar, Alipathic R groups (PROLINE, valine, leucine, isoleucine) - Aromatic non-polar R grp (Tryptophan, Tyrosine, Phenylalanine) - Polar, uncharged grp (serine, threonine, asparagine, cysteine) - Positively charged grp (LAH - Lysine, Arginine, HISTIDINE) - Negatively charged grp (NAG- Aspartate, glutamate) UNCOMMON AMINO ACIDS: Creatine - amino acid not part of a protein present in skeletal muscle Phosphocreatine + ADP ---> Creatine + ATP TRANSLATION: - 3 nucleotides form a codon - each codon codes for a specific amino acid - Methionine (AUG) --> Start codon - 3 stop/nonsense codons (UAA, UAG, UGA)

Answer 2

Haemoglobin and Myoglobin: -- Haem. - acts as an O2 transporter within the body and is present in RBCs -- Myo. - Acts as an O2 store within the musc. cells of the body - used when O2 levels drop in musc. Keratin: -- Present in all vertebrates -- Main structural component in the hair, scales, wool, feathers and nails Luciferase: -- Present in fireflies -- Catalyses the PRODUCTION of light from the protein luciferin and ATP Green fluorescent protein: -- from a jellyfish -- Fluoresces when excited with a light of a specific wavelength

Answer 3

PVT TIM HaLL Phenylalanine, Valine, Threonine, Tryptophan, Isoleucine, Methionine, Histidine, Lysine, Leucine

Answer 4

- A chiral centre is where a carbon atom is bonded to four different groups - All amino acids except glycine have their alpha carbon as a chiral centre as they're bonded to an H atom, COOH, NH2 and an R group. - Glycine has an H atom as its R group thus the alpha carbon is not a chiral centre

Answer 5

Isomers: -- They are molecules that have the same chemical formula but different chemical structures Stereoisomers: -- They are isomers with the same chemical formula and bond structure but different geometrical positioning of atoms and functional groups in the space Enantiomers: -- They are stereoisomers which are mirror images of each other but cant be superimposed on each other A molecule with ONE chiral centre can have two stereoisomers

Answer 6

- All alpha amino acids exist as either L or D enantiomers - L (levo) form amino acids are the only ones that make up all human proteins (NH3/NH2 group on left and carboxyl grp on right) - D (dextro) form amino acids are very rare and are only mainly found in peptides bacterial cell walls and some antibiotics (NH3/NH2 group on right and carboxyl grp on left)

Answer 7

Creatine in skeletal muscle cells Phosphocreatine + ADP ---- exertion----> Creatine +ATP

Answer 8

- Proline --- has a ring structure - makes proteins its present in more rigid - like in collagen (bones teeth) --- Non-polar, alipathic R group - doesnt have an R group with a linear carbon side chain - Serine and Threonine -- Polar, uncharged grps - Amide grp: Asparagine (N-glycosylation) Oxygen grp: Serine + threonine (O-glycosylation) - Proline -- Non-polar, alipathic - Tryptophan and tyrosine -- Aromatic R groups - Cysteine -- Polar uncharged group -- Contains sulfhydryl which forms disulphide bonds within and between proteins -- Strongly hydrophobic - Histidine has a positively charged R-group -- it's basic amino acids along with Lysine and Arginine -- It's the least basic of the two due to its imidazole ring - NAG -- Aspartate and Glutamate - Aromatic R groups: Tryptophan, Tyrosine, Phenylalanine These are relatively non-polar Tryptophan and Tyrosine are relatively more polar due to the presence of an N-indole ring and and OH grp respectively

Answer 9

- The sequence of codons that runs from a start to a stop codon known as a reading frame - mRNA can be read in 3 diff reading frames - The reading frame used depends on the polypeptide made - AUG determines the reading frame

Answer 10

Primary: -- The sequence of amino acids and a description of the covalent bonds linking the amino acids (peptide bonds) Secondary: -- Spatial arrangement of atoms in a protein is called its conformation -- Secondary structure describes the conformation of the polypeptide: -- Alpha helix and beta pleated sheets 2 main secondary conformations Tertiary: -- overall 3-D arrangement of 2 or more polypeptide subunits: 2 subunites: dimeric 3: trimeric 4: tetrameric Quaternary: