ch.6

Question 1

what is the basic structure of an amino acid

Answer 1

all 20 amino acids share a common structure: alpha carbon connected to an amino group and a carboxyl group

Question 2

how do amino acids differ from one another

Answer 2

they differ in the variable associated side chain (R)

Question 3

what are the three forms of amino acids

Answer 3

alpha, beta, gamma

Question 4

what defines an alpha amino acid

Answer 4

always the one bonded to the carboxyl group

Question 5

what characterizes a beta amino acids

Answer 5

a second carbon is bonded to the amino group

Question 6

what is an example of a gamma amino acid

Answer 6

Gamma-aminobutyric acid (GABA) is a gamma amino acid that functions as a neurotransmitter

Question 7

what is the role of GABA in the body

Answer 7

responsible for inhibition of neuron firing and is the most abundant neurotransmitter in the body

Question 8

which isomer of amino acids is primarily used as building blocks of proteins

Answer 8

only the L isomers are used as building blocks of proteins

Question 9

why are some amino acids considered biological buffers

Answer 9

maintain the narrow pH range of cells (7.35-7.45)

Question 10

what happens to amino acids at low pH

Answer 10

the carboxyl and amino groups accepts a proton and become protonated

Question 11

what occurs to amino acids at high pH

Answer 11

the amino and carboxyl group donate a proton and become dissociated

Question 12

what is a zwitterion

Answer 12

can donate or gain a proton and has both negative and positive groups

Question 13

what are the three classes of amino acids based on their chemical properties

Answer 13

1. nonpolar (neutral)
2. polar (made of atoms that are very electronegatively different)
3. charged (contain a charge on the R group)

Question 14

what are some examples of nonpolar amino acids

Answer 14

• leucine
• isoleucine
  -methionine (Met)
  -Tryptophan (Trp)

Question 15

what are essential amino acids

Answer 15

those that an animal cannot synthesize in sufficient amounts and must be obtained from the diet

Question 16

how many essential amino acids are there for adult humans

Answer 16

8

Question 17

what are the 8 essential amino acids

Answer 17

1. tryptophan
2. methionine
3. valine
4. threonine
5. phenylalanine
6. leucine
7. isoleucine
8. lysine

Question 18

how are amino acids linked together to form a polypeptide

Answer 18

via peptide bonds

Question 19

what forms the polypeptide backbone

Answer 19

the repeating structure of atoms forms the polypeptide backbone with side chains coming out of it

Question 20

what are the end of a polypeptide called

Answer 20

have an N-terminus (free amino end) and C-terminus (free carboxyl end)

Question 21

what is a protein

Answer 21

one or more polypeptides twisted, folded and coiled into a unique shape

Question 22

how does the sequence of amino acids affect a protein

Answer 22

determines a protein’s three-dimensional structure, which in turn determines its function

Question 23

what are the four levels of protein structure

Answer 23

1. primary
2. secondary
3. tertiary
4. quaternary

Question 24

what is the primary structure of a protein

Answer 24

the specific and unique sequence of amino acids that composes a polypeptide, determined by the nucleotide sequence of the gene that encodes the protein

Question 25

what holds the primary structure of a protein together

Answer 25

peptide bonds

Question 26

what characterizes the secondary structure of a protein

Answer 26

involves coiling and folding of the polypeptide chain stabilized by hydrogen bonds between amino group and carboxyl groups

Question 27

what are the two common forms of the secondary structure

Answer 27

alpha helix and beta pleated sheets

Question 28

what is alpha helix

Answer 28

coiled structure held in shape by hydrogen bonds common in fibrous proteins

Question 29

what is beta pleated sheet

Answer 29

structure where hydrogen bonds hold neighboring strands of sheet together, common for globular proteins

Question 30

what determines the tertiary structure of a protein

Answer 30

overall 3D shape resulting from interactions among the R groups

Question 31

what are the four possible interactions that determine tertiary structure

Answer 31

1. hydrogen bonds 2. hydrophobic interactions 3. disulfide 4. ionic bonds

Question 32

what characterizes globular proteins

Answer 32

compact combinations of alpha helix and beta pleated sheets, forming a spherical shape

Question 33

what characterizes fibrous proteins

Answer 33

mostly alpha helix and have a straight (ish) structure

Question 34

what is the quaternary structure of a protein

Answer 34

association of multiple polypeptide chains formed by interactions among the chains that comprise the protein

Question 35

do all proteins have a quaternary structure

Answer 35

no

Question 36

what is hemoglobin

Answer 36

a globular protein with four polypeptide subunits

Question 37

what is collagen

Answer 37

a fibrous protein consisting of three helical polypeptides coiled together

Question 38

how does a change in primary structure affect protein function

Answer 38

even a small change in primary structure can alter the protein's conformation and ability to function

Question 39

what is sickle cell disease

Answer 39

sickle cell disease occurs when a negatively charges amino acid is replaces by a non-polar one, altering protein folding and blood cell shape

Question 40

what is the function of molecular chaperones in cells

Answer 40

chaperonins separate new polypeptides from potentially disruptive chemical conditions within the cytoplasm and help them fold into their correct shape

Question 41

what are the two types of proteins based on polypeptide composition

Answer 41

1. monomeric: made up of one polypeptide chain 2. oligomeric: consist of two or more polypeptide chains

Question 42

what are the two types of proteins based on composition

Answer 42

1. simple protein: only made up of amino acids 2. conjugated protein: contain amino acids and some other chemical group (organic molecule or metal ion)

Question 43

what are prions

Answer 43

misfolded proteins that have become infectious agents

Question 44

what diseases are associated with prions

Answer 44

affect the structure of the brain or neural tissue and are currently untreatable and always FATAL

Question 45

what are prion diseases collectively called?

Answer 45

spongiform encephalopathies

Question 46

what causes prion diseases

Answer 46

the dysfunctional version of the protein interacts with the normal version

Question 47

what is denaturation of a protein

Answer 47

disruption and possible destruction of secondary, tertiary and sometimes quaternary structures but DOES NOT DISTURB PRIMARY STRUCTURES

Question 48

what environmental conditions can promote denaturation

Answer 48

heat, extreme pH. and alcohol can promote denaturation of proteins

Question 49

what are some diseases associated with protein denaturation

Answer 49

1. Alzheimer's: characterized by protein plaques and neurofibrillary tangles in the brain 2. Cancer: often caused by misfolding of proteins that function as tumor-suppressor agents