BIOL 2021 Lecture Notes - Lecture 19: Alpha Helix, Beta Sheet, Random Coil

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olivegoat893

9 Jul 2017

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Defined, non-random sequence of amino acids along the peptide backbone: described in two ways: Treat with 6m hcl at 110 c; 12-36 hours. Each peptide bond is broken and products are all of the free amino acids. Each amino acid is separated, identified and quantified. Final result: know how many of each amino acid present in the original. How to determine the order: determine the c-terminal amino acid. Use carboxypeptidase enzyme that removes the last (c-terminal) amino acid in a free form by breaking the peptide bond: hydrolyzes the peptide bond nearest the c-terminus, identify the n-terminal amino acids in order. Often difficult to characterize an intact protein. Instead, employ a divide and conquer approach to analyze peptide fragments of the intact protein. Use enzymes called proteases: cleave peptide bond in a specific way, two examples, trypsin cleaves on the c-terminal side of lys and arg residues, chymotrypsin cleaves on the c-terminal side of tyr, phe, and trp.

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Instructions

BACKGROUND

The amino acid sequence for a protein that is associated with the onset of Huntington's Disease in humans is 582 amino acids long and is provided below. This disease is autosomal dominant and results in a prolonged degeneration of nerve cells in the brain.

INSTRUCTIONS

For this assignment, use any method you determine most feasible (i.e. programming in MATlab, R script, Crystal Ball, Witchcraft/Hocus Pocus, etc.) to decipher the amino acid composition of this protein and answer the 15 questions associated with this protein and its associated amino acid structure.

You will be calculating proportions (percentages - %) for this assignment. Calculate all proportions to 1 decimal place and make sure you have rounded up or down correctly. If unsure, use a spreadsheet program such as Excel to display your proportional calculations to 1 decimal place.

Spelling matters (Incorrect spelling will be graded as such - incorrect).

Huntington Disease Associated Protein Amino Acid Sequence

The first amino acid below ('m') represents the amino (NH3) terminus of this protein. The last amino acid in this sequence represents the carboxy (COOH) terminus and is the very last 'c' at the bottom of this protein sequence structure. The amino acids are numbered individually across the rows (left to right) beginning from the amino terminus (#1) to the carboxy terminus (#582).

mvskreniat	hhlyqawdpv	pslspattga	lisheklllq	inperelgsm	syklgqvsih
svwlgnsitp	lreeewdeee	eeeadapaps	spptspvnsr	khragvdihs	csqfllelys
rwilpsssar	rtpailisev	vrsllvvsdl	fternqfelm	yvtltelrrv	hpsedeilaq
ylvpatckaa	avlgmdkava	epvsrllest	lrsshlpsrv	galhgilyvl	ecdllddtak
qlipvisdyl	lsnlkgiahc	vnihsqqhvl	vmcatafyli	enypldvgpe	fsasiiqmcg
vmlsgseest	psiiyhcalr	glerlllseq	lsrldaeslv	klsvdrvnvh	sphramaalg
lmltcmytgk	ekvspgrtsd	pnpaapdses	vivamervsv	lfdrirkgfp	cearvvaril
pqflddffpp	qdimnkvige	flsnqqpypq	fmatvvykvf	qtlhstgqss	mvrdwvmlsl
snftqrapva	matwslscff	vsastspwva	ailphvisrm	gkleqvdvnl	fclvatdfyr
hqieeeldrr	afqsvlevva	apgspyhrll	tclrnvhkvt	tc	CARBOXY TERMINUS

I need these decoded in order to answer the following questions:

a.) What is the name of the least abundant amino acid in this protein and what proportion of the total amino acids in the protein does this individual amino acid represent?

b.) What is the proportion of essential amino acids included in this protein sequence?

c.)How many Tryptophan residues are present in this protein sequence?

d.) The amino acid sequence from residues 73-85 is represented by the amino acids EEEWDEEEEEEAD, how would you generally classify this small region of the protein

e.) Two amino acids are present in the same proportion in this protein, which two are those?

f.) How many positively charged amino acids are present in this protein?

g.)Which class of amino acids is the most abundant in this protein?

h.) What amino acid(s) is/are present at locations 572 and 582 in the Huntington Disease protein (Full Amino Acid Name(s))

i.) What type of structure could form between these amino acids that could help stabilize this protein's structure?

j.) How many valine residues are present in this protein?

k.)Which class of amino acids is least abundant in this protein?

l.) How may negatively charged amino acids are present in the Huntington disease protein?

m.) How many Aspartic Acid residues are present in this protein and what proportion do they represent of the total amino acids in this protein?

n.)Summed together, how many hydrophilic amino acid residues are present in this protein?

o.)What is the sequence of amino acids from positions 487-492 (First letters only)?

p.) How would you classify this area of the Huntington protein based on these amino acids?

Protein Structure

a.Different function of proteins and examples:

b. Protein building blocks:

1. atomic composition of building block:

2. "parts" or "functional groups" of the building block:

c. Importance of side chain (R group):

d. Hydrophobic amino acids characteristics:

e. Hydrophilic amino acids characteristics:

f. Charged amino acids characteristics

Copy and complete the table below regarding the characteristics and which groups in the polypeptide interact together at each structural level of the protein.

	characteristics	groups interacting
Primary structure
Secondary structure
Tertiary structure
Quartenary structure

Value: 2

Choose the correct statement(s). You may choose more than one answer.

[mark all correct answers]
a. Proteins are the building blocks of amino acids.

b. Enzymes are a type of protein.

c. Quartenary structure consists of two or more polypeptide chains interacting.

d. Amino acids are made of carbon, hydrogen, nitrogen and phosphorus.

e. The primary structure of a protein is formed due to the interaction of side groups.

Value: 3

Put the following statements regarding the structural levels of a protein formation in the correct order.

Below is a sequence of events. Place them in the order they should occur, number 1 being the first item. Select the step number from the drop down next to each item.

Items to order:

1. Individual amino acids are bonded together via peptide bonds.

2. Two or more polypeptide chains interact via bonds.

3. Hydrogen bonds form between neighboring amino acids within a polypeptide chain allowing the chain to coil or form pleated sheets.

4. Side groups (R) of the individual amino acids interact with each other allowing the protein to assume its three dimensional shape.

Value:4

Put the following statements regarding the structural levels of a protein formation in the correct order

Individual amino acids are bonded together via peptide bonds.	1 2 3 4
Two or more polypeptide chains interact via bonds.	1 2 3 4
Hydrogen bonds form between neighboring amino acids within a polypeptide chain allowing the chain to coil or form pleated sheets.	1 2 3 4
Side groups (R) of the individual amino acids interact with each other allowing the protein to assume its three dimensional shape.	1 2 3 4

Value: 5

Hydrophobic amino acids will be found _______________.

a. In the interior (inner core) of a protein, away from the watery environment.

b. in the interior of a plasma membrane.

c. Both A and B

d. Neither

Value: 6

A protein's function is defined by ____________.

a. enzymatic reactions

b. it's shape.

c. chain of nucleotides.

d. the presence of carbon and hydrogen.

Value: 7

Which of the following is NOT considered a protein function?

a. transport of substances across membrane

b. enzymatic reactions

c. provides structural support

d. carries genetic information

1. The level of protein structure that is stabilized primarilyby non-covalent interactions between the side chains within asingle polypeptide chain is refered to as its:

A) primary structure

B) secondary structure

C) tertiary structure

D) quaternary structure

E) none of the above

2. Collagen, a strong fibrous protein found in connectivetissue, bone, and the extracellular matrix, has a structure inwhich three left-handed helices wind around each other to form aright-handed triple helix. The primary structure of collagen has arepeat unit of -(Gly-X-Pro)- Which of the following bonds stabilizethe collagen triple helix? (mark all that apply)

A) Hydrogen bonds between hydroxyproline residues

B) Hydrogen bonds between N-H and C=O

C) Ionic bonds between amino acid side chains

D) Hydrogen bonds between charged amino acids

3. The non-covalent forces that stabilize the Beta-strandconformation of peptides include:

A) H-bonds between amide C=O and amide NH

B) Van der Waals packing between the peptide backbone atoms

C) Van der Waals packing due to side chain interdigitation

D) Only A and B above

E) None of the above

4. What is the approximate length difference of a 22-kDasingle-stranded ?-helical protein segment vs. a 22-kDasingle-stranded ?-strand protein segment? Assume a mean residuemass of 110 Da. Show work.

5. Circular dichroism measurements have shown that the peptidebackbone of poly-l-lysine (KKKKKKK) adopts a random coilconformation at pH 7.0, but becomes ?-helical as the pH is raisedabove 10. This observation is known as the

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BIOL 2021 Lecture Notes - Lecture 19: Alpha Helix, Beta Sheet, Random Coil

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