W17 L1 - Protein Structure and Genetic Code

Flashcards about Protein Structure, Genetic Code and practical applications of DNA extraction.

What is a codon?

It is the smallest genetic unit consisting of three bases or base pairs.

How do you determine the maximum number of amino acids coded by a DNA sequence?

Divide the number of bases by three.

How many codons are in the genetic code?

64

How many different amino acids are encoded by the genetic code?

20

What are the typical stop codons?

TAG, TAA, and TGA

What is the typical start codon?

ATG

Which amino acid is the start codon equivalent to?

Methionine

What is a protein's primary structure?

It is the sequence of amino acids, dictated by DNA and mRNA.

What chemical reaction links amino acids together?

Condensation (dehydration) reaction

What molecule is removed during a condensation reaction?

Water molecule

What is the name of the bond formed between two amino acids?

Amide bond or peptide bond

Which direction do you ALWAYS write amino acid sequences?

Amino terminus to carboxy terminus

What is the peptide backbone composed of?

N-C alpha-CO

Why is the carboxy NH bond fixed with no rotation?

It cannot rotate because the electrons are smeared along this peptide bond.

What holds secondary structures together?

Hydrogen bonds in the backbone (CO and NH groups)

What are the typical secondary structures in a protein?

Alpha helix and beta sheet (beta pleated sheet)

Where do the R groups point in an alpha helix?

R groups stick out to the sides of the helix.

Where do the side chains stick out from the beta sheet

Side chains stick out up and down from the plane.

What directions can beta sheets run?

Parallel and antiparallel

What structural motifs do secondary structures give rise to?

Helix, sheet, and turn

What holds the tertiary structure of a protein together?

Interactions between the side chains (R groups).

What types of interactions are involved in tertiary structure?

Ionic interactions, hydrogen bonds, and covalent bonds (disulfide bonds)

Which amino acid is involved in forming disulfide bonds?

Cysteine

What conditions are required for disulfide bonds to form?

It requires an oxidizing environment and a basic pH (pH > 8)

Can disulfide bonds form in the cytoplasm?

No

Where are proteins with disulfide bonds located?

Endoplasmic reticulum and Golgi apparatus