Chapter 5 - Key Concepts & Review Points

Question 1

In theory, the size and composition of a polypeptide chain are ____________.

Answer 1

unlimited

Question 2

In cells, the potential polypeptide variety is limited by the efficiency of _____________ and by the ability of the polypeptide to fold into a ____________.

Answer 2

protein synthesis

functional structure

Question 3

Environmental conditions such as ______ and _____________ affect a protein’s stability during purification.

Answer 3

pH

temperature

Question 4

A(n) __________ based on a protein’s chemical or binding properties may be used to quantify a protein during purification.

Answer 4

assay

Question 5

____________ procedures take advantage of a protein’s unique structure and chemistry in order to separate it from other molecules.

Answer 5

fractionation

Question 6

____________ the salt concentration causes selective “salting out” (precipitation) of proteins with different solubilities.

Answer 6

increasing

Question 7

A protein’s ionic charge, polarity, size, and ligand-binding ability influence its ____________ behavior.

Answer 7

chromatographic

Question 8

The overall size and shape of macromolecules and larger assemblies can be assessed through ____________.

Answer 8

ultracentrifugation

Question 9

To be sequenced, a protein must be separated into individual ____________ that can be cleaved into sets of overlapping ____________.

Answer 9

polypeptides

fragements

Question 10

The amino acid sequence can be determined by ____________, a procedure for removing N-terminal residues one at a time.

Answer 10

Edman degradation

Question 11

Mass spectrometry can identify amino acid sequences from the __________________ of gas-phase protein fragments.

Answer 11

mass-to-charge ratio

Question 12

Protein sequence data are deposited in ____________.

Answer 12

online databases

Question 13

Sequence comparisons reveal the ________________ between proteins.

Answer 13

evolutionary relationships

Question 14

Protein families evolve by the ___________ and ____________ of genes encoding protein domains.

Answer 14

duplication

divergence

Question 15

The rate of evolution ________ from protein to protein.

Answer 15

varies

Question 16

The properties of proteins depend largely on the ________ and ____________ of their polypeptides.

Answer 16

sizes

sequences

Question 17

Protein purification requires controlled conditions such as ________ and ____________, and a means to quantify the protein (a(n) ________).

Answer 17

pH
temperature
assay

Question 18

Fractionation procedures are used to purify proteins on the basis of:

1. ____________
2. ____________
3. ____________
4. ____________
5. ____________

Answer 18

solubility
charge
polarity
size
binding affinity

Question 19

Difference in ____________ permit proteins to be concentrated and purified by salting out.

Answer 19

solubility

Question 20

Chromatography, the separation of soluble substances by their rate of movement through an insoluble matrix, is a technique for purifying molecules by ____________, _____________, and ____________. Binding and elution often depend on the salt concentration and pH.

Answer 20

charge (ion exchange chromatography)
hydrophobicity (hydrophobic interaction chromatography)
binding specificity (affinity chromatography)

Question 21

Electrophoresis separates molecules by ________ and ________; SDS-PAGE separates them primarily by ________. 2D electrophoresis can resolve thousands of proteins.

Answer 21

charge
size
size

Question 22

A macromolecule’s rate of sedimentation in an ultracentrifuge is related to its ________.

Answer 22

mass

Question 23

Analysis of a protein’s sequence begins with ____________, to determine the number of difference subunits, and the cleavage of ____________.

Answer 23

end group analysis

disulfide

Question 24

Polypeptides are cleaved into fragments suitable for sequencing by ____________, in which residues are removed, one at a time, from the N-terminus. Peptides can also be sequence by ____________.

Answer 24

Edman degradation

mass spectrometry

Question 25

A protein’s sequence is reconstructed from the sequences of ____________ and from information about the location of ____________. The sequences of numerous proteins are archived in publicly available databases.

Answer 25

overlapping peptide fragments

disulfide bonds

Question 26

Proteins evolve through changes in ____________. Protein sequences can be compared to construct ____________ and to identify essential amino acid residues.

Answer 26

primary sequence

phylogenetic trees

Question 27

New proteins arise as a result of the ____________ of genes or gene segments specifying protein domains, followed by their divergence.

Answer 27

duplication