Module 13: Proteins 2.0

solid phase

solid phase

A protein has a constant solubility regardless of the amount of substance present in the

salting effect

Low concentration of neutral salts increases the solubility of proteins

salting out effect

high concentrations causes precipitation of proteins

isoelectric point

Proteins are most soluble at a pH above or below their

Organic acids

are more effective than the mineral acids in liberating the amino group from its amides

ALKALIS: NaOH, KOH and Ba(OH)2

cause very rapid and complete hydrolysis but they bring about decomposition, especially the deamination of certain amino acids.

Pepsin

hydrolyzes proteins to proteoses, peptones and polypeptides only

Trypsin and ereptic enzymes

hydrolyze proteins into aminoacids but the process is slow and incomplete

Precipitation of protein molecules

refers to the settling of insoluble, solid particles of these substances in a solution

free amino groups

Proteins react with acids because of their?

alkaloidal reagents

The acids which precipitate the proteins are called _______ because they precipitate many of the alkaloids

proteinates

The metals unite with the carboxyl group, thus forming?

Dilute or aqueous solutions

What alcohol reduces the solubility of the proteins due to an increase in the electrical forces between charged particles in solutions?

denaturation

When proteins are heated, they undergo slight intermolecular rearrangement, giving rise to changes in the chemical, physical and biological properties

COAGULATION

is the clumping of the dispersed chains of denatured proteins into a solid mass that is hard to dissolve

FLOCCULATION

the denatured protein is rendered soluble at its isoelectric point but can be redissolved by adjustment of the pH

Denaturation

is the alteration of a protein structure through some form of external stress in such a way that it will no longer be able to carry out its cellular function

quaternary structure denaturation

protein sub-units are dissociated and/or the spatial arrangement of protein subunits is disrupted

Covalent interactions

interactions between amino acid side chains (such as disulfide bridges between cysteine groups)

Non-covalent dipole-dipole interactions

interactions between polar amino acid side chains (and the surrounding solvent)

Van der Waals (induced dipole) interactions

interactions  between non-polar amino acid side chains

secondary structure denaturation

proteins lose all regular repeating patterns such as alpha-helixes and betapleated sheets, and adopt a random coil configuration

Primary structure

this substances such as the sequence of amino acids held together by covalent peptide bonds, is not disrupted by denaturation

50 C

Most proteins become denatured when heated above?

globulins present in the lens

Clouding of the lens of the eye in old-age cataract is probably due to denaturating of the?

Light

Change of fibrinogen to fibrin in blood clotting may be partly due to?

agitation, trituration, surface action and high pressure

Most globular proteins are denatured by mechanical methods or forces like?

gastric juice

Digestion of proteins begins in the stomach by the secretion of?

HYDROCHLORIC ACID

acid secreted by the parietal cells

HYDROCHLORIC ACID

used to kill some bacteria and to denature proteins, making them more susceptible to subsequent hydrolysis by proteases

PEPSIN

an acid stable endopeptidase secreted by the serous cells as an inactive zymogen, pepsinogen, that is activated by HCl or autocatalytically by other pepsin molecules

serous cells

pepsin is secreted by?

Pepsin

breaks down and releases peptides and a few free amino acids from dietary proteins

TRYPSIN

secreted as trypsinogen then activated by enteropeptidase, an enzyme synthesized by the intestinal mucosal cells otherwise known as enterokinase

TRYPSIN

secreted as trypsinogen

Enteropeptidase

an enzyme synthesized by the intestinal mucosal cells otherwise known as enterokinase

Enteropeptidase

otherwise known as enterokinase

TRYPSIN

It hydrolyzes the polypeptide chain from the carboxyl end of arginine and lysine

CHYMOTRYPSIN

secreted as chymotrypsinogen and is activated by trypsin molecules

CHYMOTRYPSIN

It hydrolyzes the polypeptide chain from the carboxyl end of tryptophan, tyrosine, phenylalanine, methionine and leucine

ELASTASE

secreted as proelastase and is activated by trypsin molecules

ELASTASE

It hydrolyzes the polypeptide chain from the carboxyl end of alanine, glycine and serine

CARBOXYPEPTIDASE A

secreted as procarboxypeptidase A and is activated by trypsin molecules

CARBOXYPEPTIDASE A

It hydrolyzes the polypeptide chain from the carboxyl end of alanine, isoleucine, leucine and valine

CARBOXYPEPTIDASE B

secreted as procarboxypeptidase B and is activated by trypsin molecules

CARBOXYPEPTIDASE B

It hydrolyzes the polypeptide chain from the carboxyl end of arginine and lysine, similar to trypsin

aminopeptidase

The luminal surface of the small intestines contains?

Aminopeptidase

an exopeptidase that repeatedly cleaves the N-terminal residue from oligopeptides to produce free amino acids and smaller peptides

portal circulation

These amino acids are absorbed mainly in the small intestines through the?

active transport

Amino acids enter the cells by?

30 - 50 minutes

The absorption of amino acids is very rapid so that the maximum concentration in the blood is attaineed ____ after eating

4-8 mg per 100 ml

the amino acid nitrogen level is kept more or less constant between _______ of blood plasma

NITROGEN BALANCE OR EQUILIBRIUM

occurs when protein intake is equal or about the same as the protein breakdown

NITROGEN BALANCE OR EQUILIBRIUM

This condition is typified by young adults whose protein intake is just enough to replace the daily amount of protein used

POSITIVE NITROGEN BALANCE

implies a net gain of protein in the body

POSITIVE NITROGEN BALANCE

This is found whenever new tissues are being synthesized as in growth stage, convalescence and pregnancy

NEGATIVE NITROGEN BALANCE

implies greater protein utilization than protein intake, causing loss of protein from the body

KWASHIORKOR disease

type of malnutrition usually in children due to the inadequate intake of protein

MARASMUS

a gradual wasting away of the body, generally associated with severe malnutrition or inadequate absorption of protein and occurring mainly in young children

TISSUE PROTEINS

The amino acids pass into systemic blood to the different organs and are used as buildiing blocks for the synthesis of tissue proteins

PLASMA PROTEINS

like plasma albumin, globulin, and fibrinogen where the liver is the primary site for their biosynthesis

LABILE PROTEINS

that is important for the optimal structure and function of some important organs like liver, intestines and kidneys

The alpha-amino groups from amino acids

are the precursors in the biosynthesis of purine and pyrimidine bases of the nucleotides, porphyrins, creatine, neurotransmitters and other nitrogenous compounds

DECARBOXYLATION

refers to the removal of the carboxyl group of the amino acid for the formation of a physiologic active amine by the aid of a decarboxylase enzyme

decarboxylase enzyme

DECARBOXYLATION refers to the removal of the carboxyl group of the amino acid for the formation of a physiologic active amine by the aid of?

TRANSAMINATION

refers to the removal of the amino group that begins with the transfer of this amino group to an amino group acceptor, usually alpha-ketoglutarate that eventually turns into glutamate

TRANSAMINATION

This reaction is catalyzed by a transaminase

alpha – keto acid or a carbon skeleton -

After transamination, the amino acid turns into an?

alpha – keto acid or a carbon skeleton -

It turns into acetyl-coA, pyruvate or other intermediates and is oxidized to produce biochemical energy (ATP) via the Kreb’s cycle with the release of carbon dioxide and water.

alpha – keto acid or a carbon skeleton -

It is converted into a carbohydrate or fat molecule

alpha – keto acid or a carbon skeleton

It is reaminated to form amino acids

OXIDATIVE DEAMINATION

once the amino groups have all been collected in the form of glutamate, this substance undergoes oxidative deamination to reform alpha-ketoglutarate and release ammonia

ammonia

It is utilized for the synthesis of non-protein nitrogenous compounds

ammonia

It enters the ornithine cycle for the formation of urea

ammonia

It is detoxified for the synthesis of glutamine

Ketogenic amino acids

are amino acids whose catabolism yields either acetoacetate or one of its precursors, acetyl CoA or acetoacetyl CoA

are the only exclusively ketogenic amino acids found in proteins.

Glucogenic amino acids

are amino acids whose catabolism yields pyruvate or one of the intermediates of the citric acid cycle

Glucogenic amino acids

These intermediates are substrates for gluconeogenesis and therefore can give rise to the net formation of glycogen in liver and muscle

PHENYLKETONURIA / PHENYLPYRUVIC OLIGOPHRENIA

due to the absence of the enzyme phenylalanine hydroxylase which converts phenylalanine to tyrosine

PHENYLKETONURIA / PHENYLPYRUVIC OLIGOPHRENIA

Phenylalanine is instead converted into phenylpyruvic acid which impairs normal development of childs brain leading to mental retardation

phenylalanine hydroxylase

converts phenylalanine to tyrosine

TYROSINOSIS

due to the absence of hydroxyphenylpyruvic acid oxidase

TYROSINOSIS

In here, hydroxyphenylpyruvic acid is not oxidized into homogentesic acid

ALKAPTONURIA

due to the absence of homogentisic acid oxygenase

ALKAPTONURIA

When the urine containing homogentesic acid is exposed to the atmosphere, it turns black due to oxidation

is needed for the activity of the enzyme.

ochronosis

abnormal pigmentation of cartilages, fibrous tissues and tendons

homogentisic acid oxygenase

an iron containing enzyme which catalyzes the oxidation of homogentisic acid to fumarate and acetate

ALBINISM

due to the absence of the enzyme tyrosinase

Tyrosinase

converts tyrosine into DOPA (L-3,4dihydroxyphenylalanine) convertible to melanin