Proteins Flashcards
How many proteinogenic amino acids are there? How many of them are essential?
21 AAs, 9 of which are essential
Is plant or animal protein % higher?
animal
What are the 4 components of an amino acid?
- animo terminal (amino group)
- carboxyl terminal (carboxylic acid group)
- alpha-carbon
- side chain (different for all AAs)
What are enantiomers?
structures that have only 1 difference
What are Zwitterions?
the same AA, but at different pHs (COO- vs COOH, etc.)
the only thing that differs between AAs is…
side chain
“protein” refers to the…
(in terms of structure)
3D structure
“peptide” refers to the…
(in terms of structure)
2D structure
are “protein” and “peptide” interchangable terms?
Nope
What kind of bond forms between 2 AAs?
peptide / amide bond
how are peptide bonds formed?
condensation reactions – loss of water
how are peptide bonds broken?
hydrolysis reaction – addition of water
what is a primary structure?
the sequence of AAs
what is a secondary structure?
the backbone structure (alpha-helix vs beta-sheet)
what is a tertiary structure?
3D arrangement
What is a quaternary structure?
≥ 2 tertiary structures together (subunits)
What does it mean when a proteins is in a native state?
its normal and fine
What does it mean when a proteins is in a denatured state?
impaired protein structure and function
Whats a dipeptide?
2 AAs joined by a peptide bond
Whats a tripeptide?
3 AAs joined by peptide bonds
Whats a oligopeptide?
~ 50 AAs joined by by peptide bonds
whats a polypeptide?
> 50 AAs joined by peptide bonds
What are the Basic AAs?
(For bonus points, what puts them in this category, and are they polar or non-polar)
Lysine, Arginine, Histadine
(they have a positive charge, and are polar)
What are the Acidic AAs?
(For bonus points, what puts them in this category, and are they polar or non-polar)
Aspartate, Glutamate, Asparagine, Glutamine
(they have a negative charge, and are polar)
What are the Hydroxylated AAs?
(For bonus points, what puts them in this category, and are they polar or non-polar)
Serine, Threonine (technically also Tyrosine)
(have an OH-group on the side chain, and are polar)
What are the Neutral AAs?
(For bonus points, what puts them in this category, and are they polar or non-polar)
Glycine, Alanine
(have no charge on the side chain, and are non-polar)
What are the Branched Chain AAs?
(For bonus points, what puts them in this category, and are they polar or non-polar)
Leucine, Isoleucine, Valine
(have branched side chain w no charges, and are non-polar)
What are the Aromatic AAs?
(For bonus points, what puts them in this category, and are they polar or non-polar)
Phenylalanine, Tyrosine, Tryptophan, Proline
(have aromatic rings, and are non-polar – except for tyrosine)
What are the Sulfur-Containing AAs?
(For bonus points, what puts them in this category, and are they polar or non-polar)
Cystine, Methionine
(have sulfur-group and are non-polar)
Which AAs are essential? (9)
Lysine, Histadine, Threonine, Leucine, Isoleucine, Valine, Phenylalanine, Tryptophan, Methionine
Which AAs are non-essential? (11)
Arginine, Aspartate, Glutamate, Asparagine, Glutamine, Serine, Glycine, Alanine, Tyrosine, Proline, Cystine
Where are proteins digested? By what, and how?
- mostly in the stomach by HCl* (denatures proteins and activates pepsin)*
- in the small inestine by zymogens (does breakdown and absorbtion)
What secretes HCl?
parietal cells, whe triggered by gastrin, acetylcholine, and histamine
What releases zymogens?
pancrease
What are the types of endopeptidases (5) and what do they do?
- trypsin
- elastase
- pepsine
- parapepsine
- chymotrypsin
(cleave the internal peptide bonds of the protein)
Where does trypsin attack?
basic components
Where does elastase attack?
neutral aliphatic components
Where does pepsine/parapepsin/chymotrypsin attack?
large nuetral components
What are the types of exopeptidases, and what do they do?
- amino-peptidases
- carboxy-peptidases
(cleave the terminal peptide bonds of a protein)
Where do amino-peptidases attack?
amino-terminal component
Where do carboxy-peptidases attack?
carboxyl-terminal component
describe what trypsin does in terms of protein digestion / absorbtion
- trypsinogen is secreted from the pancreas (along with inactivated zymogens/proenzymes)
- enteropeptidase located within the border border activates it into trypsin
- trypsin activates other zymogens (chymotrypsin, elastase and carboxy-peptidases)
How are AAs absorbed after being digested?
(2 processes that occur within the small intesine)
Facilitated Diffusion
OR
Active Transport (>60 of AAs)
- done w sodium-dependent transporters (peptide transporter 1 / PEPT1)
- indirect ATP requirement and concentration gradient
What happens to proteins have absorbtion?
liver uptakes AAs from circulation
- ~20% used to make peptide hormones
- ~80% are catabolized, and products are brought elsewhere (krebs cycle, urea cycle, gluconeogensis, lipogenesis)
What aspects contribute to protein quality?
- AA Composition (essential AAs are high quality)
- Digestibility (more digestible protein are high quality)
- Presence of Toxic Factors (less toxic means high quality)
- Species Consuming the Protein (ruminants consume low quality)
What is Protein Efficiency Ratio (PRE)?
PER = gain in body mass (g) / total protein intake (g)
- based on rats eating diet w specific bordrline protein consumption – developmental issues mean protein is of bas quality (but doesnt tell you why)
- optimal value is 2.0 (based on egg)
What is Chemical Score (CS)?
CS = (abundance of first limiting AA in the test protein / abundance of the same AA in whole egg) x 100%
- chemically digested than quantified w chromatography
- doesn’t account for toxins/digestibility
- use chart, and find value ratio w the smallest number – that is the limiting AA in the sample
What is a Nitrogen Balance (NB)?
NB = nitrogen intake - nitrogen loss
- NB > 0; growing/pregnany/healing
- NB < 0; not enough protein
- NB = 0; normal and healthy
What is the Atkins diet? What is the C:F:P ratio?
- high protein diet
- 3 : 64 : 33
What is the South Beach diet? What is the C:F:P ratio?
- high protein diet
- 30 : 40 : 30
(slightly better than Atkins)
Are high protein diets good?
no
Should you suppliment proteins
not unless you’re an elder
What is Marasmus?
- protein AND calorie deficiency
- adults deal better than children
- loss of muscle, fat, skin, etc.
What is Kwashiorkor?
- protein deficiency
- common in developing country children
- enlarged abdomen due to osmotic embalance in the gut and enlarged liver
AAs are catabolized into what? Where do the products go?
- Carbon skeleton (alpha-ketoacid) (x2) that goes to the Kreb’s Cycle
- NH3 (ammonia) / NH4+ (ammonium) (x1) that enter the Urea Cycle
the alpha-ketoacid for glutamate is…
alpha-ketoglutarate
the alpha-ketoacid for aspartate is…
oxaloacetate
the alpha-ketoacid for alanine is…
pyruvate
What is a Transamination?
- the transfer of an amino-group from one AA (donor) to another (acceptor)
- catalyzed by aminotransferases (GPT or GOT)
- can be bidirectional
- active in all tissues
What is an Oxidative Deamination?
- ammonia is released from a glutamate backbone
- catalyzed by glutamate dehydrogenase w NAD+
- active in all tissues
- yields a NH4+ that can be used for glutamine synthesis, urea synthesis, or excreted as urine
What is Glutamine Production?
- production of a glutamine from glutamate
- active in muscles
- catalyzed by glutamine synthetase w ATP and NH4+
What is Glutamate Regeneration?
- regeneration of glutamate from glutamine
- catalyzed by glutaminase
- yields a NH4+
- active in liver (fed) and kidney (fasted)
What is the Urea Cycle?
- NH4+ is converted into urea to prevent neurotoxicity
- HCO3- and NH4+ enter, and w ATP and a milltion other enzymes and cofactors urea is produced
What does it mean for an AA to be ketogenic?
the AA can be degrated to form Acetyl CoA
(most AAs are keto and gluco, but leucine and lysine are keto only)
What does it mean for an AA to be glucogenic?
the AA can be degrated to form glucose
(most AAs are keto and gluco, but leucine and lysine are keto only)
