Why are nearly all amino acids in organisms left-handed(exception is glycine which has no isomer) when abiotic samplestypical have an even mix of left- and right-handed molecules?

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Irving HeathcoteLv2

27 Jul 2018

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1. In humans, right-handedness (R) is dominant to left-handedness (r), and brown eyes (B) are usually dominant to blues eyes (b).

a) What are the genotypes of gametes produced by a person heterozygous for both traits?

b) What are the genotypes of gametes for a person heterozygous for brown eyes, but homozygous recessive for left-handedness?

c) Set up a Punnett square for a couple that is heterozygous for both traits. What is the probability that if their first child is brown-eyed and left-handed that the second child is blue-eyed and left-handed?

d) A right-handed, blue-eyed woman marries a right-handed, brown-eyed man. They have two children, one left-handed and brown-eyed and the other right-handed and blue-eyed. By a later marriage with another man, who is also right-handed and brown-eyed, she has seven more children, all of whom are right-handed and brown-eyed. What are the genotypes of the woman and her two husbands?

Read the following statements carefully and determine which are true and which are false.

i) The energy required to synthesize nucleic acids comes from the nucleotide building blocks themselves.
ii) The "groove" in the structure of double-stranded DNA allows binding interactions between proteins and particular base sequences.
iii) In double-stranded DNA, the two strands are wound around one another in a right-handed helix.

i) & ii) are true, and iii) is false.

i) & iii) are false, and ii) is true.

i) is false, and ii) & iii) are true.

All three statements are false.

All three statements are true.

fuchsiascorpion780

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