Proteins and Nucleic Acids — Structure and DNA/RNA Basics

A set of Q&A flashcards covering protein structure, protein bonds, quaternary structure, hemoglobin, collagen, heme, and DNA/RNA fundamentals (nucleotides, bases, pairing, phosphodiester bonds, double helix, Chargaff's rules, Franklin, and central dogma).

What are the four levels of protein structure discussed in the notes?

Primary, Secondary, Tertiary, and Quaternary structure.

Which bonds contribute to tertiary structure in proteins?

Ionic, hydrogen, and covalent bonds (including disulfide bridges between cysteine residues).

What is a disulfide bridge in proteins?

A covalent bond between cysteine residues that helps stabilize the folded protein.

What defines quaternary structure in proteins?

The association of two or more polypeptide units to form the full protein; not all proteins have this level.

Name a protein commonly cited as having a quaternary structure.

Hemoglobin.

What structural feature sets collagen apart from alpha helix or beta sheet?

Collagen has three polypeptide strands (triple-helix) and lacks typical alpha helices or beta sheets.

What is the role of heme in hemoglobin?

Heme is a prosthetic group that binds oxygen, enabling hemoglobin to carry oxygen in blood.

What is the central dogma as described in these notes?

DNA is transcribed into RNA, which is translated into protein; involves ribosomes and mRNA/rRNA.

What is a nucleotide composed of?

A phosphate group, a sugar, and a nitrogenous base.

List the bases for DNA and RNA and note any special cases.

DNA: A, T, C, G; RNA: A, U, C, G. RNA uses U instead of T.

What are purines and pyrimidines?

Purines: A and G; Pyrimidines: C, T (DNA) and U (RNA).

Which base pairs pair with which, and how many hydrogen bonds do they form?

A pairs with T (or U in RNA) with 2 H-bonds; G pairs with C with 3 H-bonds.

What is a phosphodiester bond?

A covalent bond linking the phosphate of one nucleotide to the 3’ carbon of the next sugar, forming the backbone of DNA/RNA.

Describe DNA's double helix and strand orientation.

Two strands hydrogen-bond through base pairing; strands are antiparallel: one runs 5’→3’, the other 3’→5’.

What are Chargaff's rules?

In DNA, A equals T and G equals C; base pairing explains the constant width of the double helix.

What did Rosalind Franklin contribute to the discovery of DNA structure?

X-ray diffraction images revealing the distance between strands and a helical structure.

What RNA components are mentioned in relation to the central dogma?

mRNA and rRNA (translation occurs on ribosomes).

What is a key structural difference between DNA and RNA?

RNA has a 2’–OH group and uses uracil (U); DNA uses deoxyribose and thymine (T).

Why is hydrogen bonding important in base pairing?

Hydrogen bonds hold the two DNA strands together; G–C has 3 bonds, A–T (or A–U) has 2 bonds.

Why does the DNA double helix maintain a constant width?

A–T and G–C pairing (purine–pyrimidine) maintains a uniform diameter.

What does antiparallel mean in the context of DNA strands?

The two strands run in opposite directions: one 5’→3’, the other 3’→5’.

What do the 5’ and 3’ carbons signify in nucleotide polymerization?

5’ end bears the phosphate; 3’ end is where the next nucleotide is added; polymerization proceeds 5’→3’.

What is the polymeric nature of DNA and RNA?

Both are polymers made of repeating nucleotides; monomers are nucleotides.