Question

Compare and contrast the following for both nucleic acids and proteins:

What determines directionality? At which end do you start synthesizing the molecule?

What are the monomers called?

What is the name of the bond that links the monomers and what type of bond

is it?

What is the variable portion of the monomer and what is the constant portion?

Compare and contrast the structure, function and properties of DNA and RNA.

3. Briefly describe how different amino acid sequences can lead to different protein structures and functions. Be sure to refer to the different levels of protein folding.

4. Briefly describe the properties of lipid bilayers and how this dictates membrane permeability. Be sure to mention which types of molecules can and cannot pass through the lipid bilayer.

5. Describe the different types of membrane transport and how they relate to concentration gradients and energy.

Answer 1

Q.1 All nucleotides in a polynucleotide have the same orientation. Polynucleotides are formed by the condensation of two or more nucleotides. The condensation most commonly occurs between the alcohol of a 5`-phosphate of one molecule and the 3`-hydroxyl of a second, with the elimination of H²O, forming a phosphodiester bond. The primary structure of DNA and RNA proceeds in the 5`3` direction.

Proteins are unbranched structures constructed from 22 standard a-amino acids. They have 4 levels of structural organizations; primary, secondary, tertiary and quaternary. The primary structure is the amino acid sequence which is specified by genetic information. The amino acids are linked by peptide bonds which are amide linkages formed between an a-amino group of one amino acid and a-carboxyl group of another amino acid in the NC direction, with the release of a molecule of water.DNA is double-stranded whereas RNA is a single-stranded

Q. 2.DNA and RNA contain the pentose sugar deoxyribose and ribose respectively.

RNA is not limited to the nucleus like DNA.

Three nitrogenous bases are common to both the species i.e adenine, guanine and cytosine, however, the fourth base is different. DNA contains thymine while as RNA has uracil.

Q.3. Primary structure of polypeptide (amino acid sequence) determines the higher levels of structural organization.

Secondary structures are represented by most common forms, a-helix and the B-pleated sheet. Both patterns are stabilized by H-bonds.

Tertiary structures refer to the unique three-dimensional conformations that globular proteins assume as a consequence of the interactions between the side chains in their primary structure. The following types of covalent and non-covalent interactions stabilize the tertiary structure,

a) Hydrophobic interactions

b) Hydrogen bonds

c) Electrostatic interactions

d) van der Wals forces

e0 Covalent bonds