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Proteins Reviewer
Medical Technology (MD)
Our Lady of Fatima University
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PROTEINS (p; 727/1065) Stoker
A protein is a naturally occurring, unbranched polymer in which the monomer units are amino acids. - In electrophoresis – they move towards the cathode (positive region) because they are negatively charged.
A typical human cell contains about 9000 different kinds of proteins, and the human body contains about 100,000 different proteins.
Needed for:
- The synthesis of enzymes, certain hormones, and some blood components;
- The maintenance and repair of existing tissues for the synthesis of new tissue; and
- Sometimes for energy.
CHARACTERISTICS OF PROTEINS
- Next to water, PROTEINS ARE THE MOST ABUNDANT SUBSTANCES IN NEARLY ALL CELLS
- 15% of overall cell mass and almost half of cell dry mass
- All proteins consist of CARBON, OXYGEN, HYDROGEN, NITROGEN, and , for some of them , SULFUR.
Identifying feature from other substances (like carbs and lipids): PRESENCE OF NITROGEN
- 15% is the average nitrogen content of proteins by mass
Casein , the main protein of milk, contains phosphorus, an element very important in the diet of infants and children.
Hemoglobin , the oxygen-transporting protein of blood, contains iron.
AMINO ACIDS: THE BUILDING BLOCKS FOR PROTEINS
- An amino acid is an organic compound that contains both an amino (NH2) group and a carboxyl (COOH) group.
- Always a-amino acids – an amino acid in which the amino group and the carboxyl group are attached to the a-carbon atom.
- There are 700 known naturally occurring amino acids but only 20 (the 20 standard a-amino acids) are normally present in proteins.
- General structural formula for an a-amino acid :
Side chain - R-group - Distinguishes a-amino acids from each other
- Vary in size, shape, charge, acidity, functional groups present, hydrogen-bonding ability, and chemical reactivity
Standard amino acid - The 20 a-amino acids normally found in proteins.
Groupings according to side chain polarity (1) nonpolar amino acids (2) polar neutral amino acids (3) polar acidic amino acids and (4) polar basic amino acids.
(1) NONPOLAR AMINO ACIDS ▪ GAVLIPP MT (Glycine, Alanine, Valine, Leucine, Isoleucine, Proline, Phenylalanine, Methionine, Tryptophan) ▪ A nonpolar amino acid is an amino acid that contains one amino group, one carboxyl group, and a nonpolar side chain. ▪ Hydrophobic – water-fearing ▪ Normally found in the interior of proteins, where there is minimal contact with water. ▪ There are 9 nonpolar amino acids
Glycine (Gly, G) - The only achiral among the 20 standard a- amino acids. - Has 2 Hydrogens Alanine (Ala, A) - 1 CH
Valine (Val, V) – V-like side chain Leucine (Leu, L) – CH3 in the middle of side chain Isoleucine (Ile, I) – Reversed L-shaped side chain
The nonpolar amino acid proline has a structural feature not found in any other standard amino acid. Its side chain, a propyl group , is bonded to both the a-carbon
atom and the amino nitrogen atom, giving a cyclic side chain.
Proline (Pro, P) – 1 propyl cyclic group Phenylalanine (Phe,F) – 1 phenyl group as side group
Methionine – S-group as side chain Tryptophan – 2 cyclic groups
Tryptophan ▪ a borderline member of this group because water can weakly interact through hydrogen bonding with the NH ring location on tryptophan’s side-chain ring structure. Thus, some textbooks list tryptophan as a polar neutral amino acid
(2) POLAR NEUTRAL AMINO ACIDS ▪ SCATT G (Serine, Cysteine, Asparagine, Threonine, Tyrosine, Glutamine) ▪ A polar neutral amino acid is an amino acid that contains one amino group, one carboxyl group, and a side chain that is polar but neutral. ▪ Side chain pH – neither basic nor acidic ▪ More soluble to water. The R-group can hydrogen bond to water. ▪ There are 6 polar neutral amino acids
Serine (Ser, S) – CH2 & OhH as side chain Cysteine (Cys, C) – SH group as side chain Threonine (Thr, T)– V-shaped with OH side chain Aspargine (Asn, N) – Small y-shaped with O-double bond and NH2 side chain Glutamine (Gln, Q) – Big Y-shaped side chain with O- double bond and NH
Tyrosine (Tyr, Y) – has a cyclic group with an OH
(3) POLAR ACIDIC AMINO ACIDS
▪ AG (Aspartic acid, Glutamic acid) ▪ A polar acidic amino acid is an amino acid that contains one amino group and two carboxyl groups , the second carboxyl group being part of the side chain. ▪ Side chain pH - The side chain is negatively charged - The side-chain carboxyl group has lost its acidic hydrogen atom - The nitrogen atom of the amino group has accepted a proton ▪ There are only 2 polar acidic amino acids Aspartic acid (Asp, D) – small y-shape like Asparagine but has OH Glutamic acid (Glu, E) – big Y-shape like Gutamin but has OH (4) POLAR BASIC AMINO ACIDS ▪ HLA (Histidine, Lysine, Arginine) ▪ A polar basic amino acid is an amino acid that contains two amino groups and one carboxyl group, the second amino group being part of the side chain. ▪ There are only 3 polar basic amino acids ▪ Side chain pH
- The side chain is positively charged
- The side-chain carboxyl group has lost its acidic hydrogen atom
Histidine (His, H) – Has a cyclic group with HN & N in its side chain Lysine (Lys, K) – straight unbranched chain with NH2 at the end Arginine (Arg, R) – branched chain with NH2 & C double bonded to NH
All of the standard amino acids are necessary constituents of human proteins. Adequate amounts of 11 of the 20 standard amino acids can be synthesized from carbohydrates and lipids in the body if a source of nitrogen is also available.
ESSENTIAL AMINO ACIDS - An essential amino acid is a standard amino acid needed for protein synthesis that must be obtained from dietary sources because the human body cannot synthesize it in adequate amounts from other substances.
ACID–BASE PROPERTIES OF AMINO ACIDS
Amino acids - THEY ARE WHITE CRISTALLINE SOLIDS IN PURE FORM - HAVE HIGH DECOMPOSITION - Most amino acids decompose before they melt. - NOT WATER SOLUBLE - because of strong intermolecular forces within their crystal structures. Studies of amino acids confirm that they are charged species both in the solid state and in solution. - ACIDIC GROUP (-COOH) – can lose protons in neutral solution and becomes negatively charged - BASIC GROUP (-NH2) – can accept protons in neutral solution and becomes positively charged - internal acid–base reaction
ZWITTERION - A zwitterion is a molecule that has a positive charge on one atom and a negative charge on another atom, but which has no net charge. - The product produced from internal acid-base reaction of an amino acid
Changes as the pH of the solution changes
In an acidic solution, the zwitterion accepts a proton (H1) to form a positively charged ion.
In basic solution, the -NH3 of the zwitterion loses a proton, and a negatively charged species is formed.
For acidic or basic amino acids, the side chain can also acquire a charge because it contains an amino or a carboxyl group that can, respectively, gain or lose a proton.
ISOELECTRIC POINTS
- An isoelectric point is the pH at which an amino acid exists primarily in its zwitterion form.
- 99% of amino acids have an isoelectric point
- Fifteen of the 20 amino acids, those with nonpolar or polar neutral side chains, have isoelectric points in the range of 4–6.
- The three basic amino acids have higher isoelectric points.
- The two acidic amino acids have lower ones
CYSTEINE: A CHEMICALLY UNIQUE AMINO ACID - Has sulfhydryl group - Can form cystine, a dimer, using a mid oxidizing agent through oxidation-reaction - Cystine is linked via covalent disulfide bonds, commonly seen in thiol reactions
PEPTIDES - A PEPTIDE is an unbranched chain of amino acids. - Covalently bonded - Dipeptide – a compound with 2 amino acids - Tripeptide – with 3 amino acids - Oligopeptide – loosely used to refer to peptides with 10 to 20 amino acid residues - Polypeptide – a long unbranched chain of amino acids.
NATURE OF PEPTIDE BONDS - PEPTIDE BOND
- A peptide bond is a covalent bond between the carboxyl group of one amino acid and the amino group of another amino acid.
- Amino acids react with each other to form amide bonds (peptide bonds)
- The -COOH (carboxyl group) of one amino acid reacts with the -NH2 (amino group) of the other and are linked through amide bonds (peptide bonds)
- H2O is one of the product
- N-terminal end – the free -NH3 at the left
- C-terminal end – the free -COOH at the right
- AMINO ACID RECIDUE
- An amino acid residue is the portion of an amino acid structure that remains, after the release of H2O, when an amino acid participates in peptide bond formation as it becomes part of a peptide chain.
Backbone of peptide – the repeating sequence of peptide bonds and a-carbon —CH groups in a peptide.
Thus, structurally, a peptide has a regularly repeating part (the backbone) and a variable part (the sequence of R groups). It is the variable R group sequence that distinguishes one peptide from another.
PEPTIDE NOMENCLATURE
Small peptides are named as derivatives of the C- terminal amino acid that is present.
The IUPAC rules for doing this are:
Rule 1 : The C-terminal amino acid residue (located at the far right of the structure) keeps its full amino acid name.
Rule 2 : All of the other amino acid residues have names that end in -yl. The -yl suffix replaces the -ine or -ic acid ending of the amino acid name, except for tryptophan (tryptophyl), cysteine (cysteinyl), glutamine (glutaminyl), and asparagine (asparaginyl).
Rule 3 : The amino acid naming sequence begins at the N-terminal amino acid residue.
ISOMERIC PEPTIDES
- Peptides can have constitutional isomers – contains the same amino acid molecule but in different order with diff properties.
BIOCHEMICALLY IMPORTANT SMALL PEPTIDES
SMALL PEPTIDE HORMONES
- Both from pituitary glands: oxytocin and vasopressin
- Nanopeptides with six of the residues held in the form of a loop by a disulfide bond formed from the interaction of two cysteine residues
- Differ in positions 3 and 8
- Estradiol – has amine and alcohol
- Precursor/platform molecule – cholesterol (has alcohol group)
Oxytocin - Regulates uterine contractions and lactation.
Vasopressin - Regulates the excretion of water by the kidneys; it also affects blood pressure. - Aka antidiuretic hormone (ADH) – function in the kidneys, which is to decrease urine output in order to decrease water elimination from the body. Such action is necessary when the body becomes dehydrated.
SMALL PEPTIDE NEUROTRANSMITTERS
Enkephalins - Are pentapeptide neurotransmitters produced by the brain itself that bind at receptor sites in the brain to reduce pain (short-term). - Associated with the <high= feeling by long distance runners to manage the game despite being injured, and in acupuncture.
PROTEIN STRUCTURE CLASSIFICATION
PRIMARY STRUCTURE OF PROTEINS
- Primary protein structure is the order in which amino acids are linked together in a protein.
- Every protein has its own unique amino acid sequence.
- Primary protein structure always involves more than just the numbers and kinds of amino acids present; it also involves the order of attachment of the amino acids to each other through peptide bond
- Sequencing procedures involve automated methods that require relatively short periods of time (days).
- The primary structure of a specific protein is always the same regardless of where the protein is found within an organism.
INSULIN - The hormone that regulates blood-glucose levels - Was the first protein for which primary structure was determined; the <sequencing= of its 51 amino acids (21:30) was completed in 1953, after eight years of work by the British biochemist Frederick Sanger. - Primary structures of insulin from cows, pigs, sheep, and horses is similar to human insulin
MYOGLOBIN
a protein involved in oxygen transport in muscles
contains 153 amino acids assembled in the particular definite order
The various amino acids present in a protein, whose order is the primary structure of the protein, are linked to each other by peptide linkages.
The peptide bonds are part of the <backbone= of the protein.
The structural characteristics of a protein backbone are the same as those of a peptide backbone (Section 20); relative to backbone structure, a protein is simply an <extra long= peptide.
A representative segment of a protein backbone is as follows:
Geometric characteristics of peptide bonds - The C and N of protein backbone are arranged in a zigzag pattern
- The peptide linkages are essentially planar. This means that for two amino acids linked through a peptide linkage, six atoms lie in the same plane: the a-carbon atom and the C=O group from the first amino acid and the N—H group and the a- carbon atom from the second amino acid.
- The planar peptide linkage structure has considerable rigidity, which means that rotation of groups about the C—N bond is hindered, and cis–trans isomerism is possible about this bond. The trans isomer orientation is the preferred orientation , as shown in the preceding diagram. The O atom of the C=O group and the H atom of the N—H group are positioned trans to each other.
SECONDARY STRUCTURE OF PROTEINS
- Secondary protein structure is the arrangement in space adopted by the backbone portion of a protein.
- HYDROGEN BONDING – responsible for this type of interaction.
- hydrogen bonding between a carbonyl oxygen atom of a PEPTIDE LINKAGE and the hydrogen atom of an amino group of another peptide linkage farther along the protein backbone.
- Very few proteins have entirely a helix or b pleated sheet structures; they are only present when R groups are small
- It is possible to have both a helix and b pleated sheet structures within the same protein
THE ALPHA HELIX - An alpha helix structure is a protein secondary structure in which a single protein chain adopts a
shape that resembles a coiled spring (helix), with the coil configuration maintained by hydrogen bonds between N—H and C=O groups.
The twist of the helix forms a right-handed, or clockwise, spiral.
The hydrogen bonds between C=O and N—H entities are orientated parallel to the axis of the helix (Figure 20).
A given hydrogen bond involves a C=O group of one amino acid and a N—H group of another amino acid located four amino acid residues further along the spiral (Figure 20). This is because one turn of the spiral includes 3 amino acid residues.
All of the amino acid R groups extend outward from the spiral (Figure 20). There is not enough room for the R groups within the spiral.
THE BETA PLEATED SHEET
- A beta pleated sheet structure is a protein secondary structure in which two fully extended protein chain segments in the same or different molecules are held together by hydrogen bonds.
- Hydrogen bonds form between oxygen and hydrogen peptide linkage atoms that are either in different parts of a single chain that folds back on itself ( intrachain bonds ) or between atoms in different peptide chains in those proteins that contain more than one chain ( interchain bonds ).
- In molecules where the b pleated sheet involves a single molecule, several U-turns in the protein chain arrangement are needed in order to form the structure.
Human insulin, a protein that has two peptide chains and a total of 51 amino acid residues; both inter- and intramolecular disulfide bonds are present in its structure.
ELECTROSTATIC INTERACTIONS (SALT BRIDGES) - Always an interaction between acid (negatively charged) and base (positively charged) R groups at an appropriate pH. - —COOH group becomes —COOH– group - —NH2 group becomes —NH3 group - Positive–negative ion–ion attraction
HYDROGEN BOND - Occur with POLAR R GROUPS of amino acids - Weak bond - pH and temperature sensitive
HYDROPHOBIC INTERACTIONS
- Occurs when 2 NONPOLAR SIDE CHAINS are closed to each other
- LONDON FORCES – resulting from the momentary uneven distribution of electrons within the side chains
- Common between phenyl rings and alkyl side chains.
- The WEAKEST BOND INDIVIDUALLY but can be stronger than hydrogen bond if in terms of cumulative effect of many hydrophobic interactions.
Figure 20 Disulfide bonds, electrostatic interactions, hydrogen bonds, and hydrophobic interactions are all stabilizing influences that contribute to the tertiary structure of a protein.
MYOGLOBIN
• 1959 –
tertiary structure of protein was discovered
- Conjugated protein
- Function: oxygen storage in tissue
- Single peptide chain of 153 amino acids with numerous a helix segments within the chain
- Prosthetic heme group: an iron-containing group with the ability to bind molecular oxygen.
QUATERNARY STRUCTURE OF PROTEIN - Quaternary protein structure is the organization among the various peptide chains in a multimeric protein. - Highest level of protein organization - Only in MULTIMERIC PROTEINS – have 2 or more peptide chains - NOT COVALENTLY BONDED - Most multimeric proteins contain an even number of subunits (two subunits 5 a dimer , four subunits 5 a tetramer, and so on). The subunits
are held together mainly by HYDROPHOBIC INTERACTIONS between amino acid R groups.
- Noncovalent interactions (electro-static interactions, hydrogen bonds, and hydrophobic interactions)
- Responsible for maintenance
- Easily disrupted
HEMOGLOBIN - Oxygen-carrying protein in blood - It is a tetramer in which there are two identical a chains and two identical b chains. Each chain enfolds a heme group, the site where oxygen binds to the protein.
PROTEIN HYDROLYSIS
- Reverse reaction of the formation of peptide linkages
- STRONG ACID/BASE IN HEAT
- The peptide bonds of the amino acid chain are hydrolyzed and free amino acids are produced.
- Product: Amino acids with carboxylic acid and amine functional groups
- Application:
- Protein digestion is simply enzyme-catalyzed hydrolysis of ingested protein. The free amino acids produced from this process are absorbed through the intestinal wall into the bloodstream and transported to the liver. Here they become the raw materials for the synthesis of new protein.
- The hydrolysis of cellular proteins to amino acids is an ongoing process, as the body resynthesizes needed molecules and tissue.
Note: The amino acids are positive due to the acidic environment — they’ll be negative if it is a basic environment.
Protein digestion
PROTEIN DENATURATION - Protein denaturation is the partial or complete disorganization of a protein’s characteristic three-dimensional shape as a result of disruption of its secondary, tertiary, and quaternary structural interactions. - Renaturation – restoration process from limited denaturation - Result: Loss of biochemical activity - Loss of water solubility: coagulation - Eye damage - Coagulation – The precipitation out of biochemical solution of denatured protein. - Activities: - Heat application : cooking, cauterization (wound sealing using heat), sterilizing surgical materials, canned foods, body temp. - Ionizing radiation : UV - Acid reaction : HCl in stomach denatures casein (milk protein); Lactic acid in milk souring, cheese, and yogurt (skim milk) - Alcohol application: Isopropyl alcohol ( Carbon) is better than ethyl (2 Carbon) due to longer contact time
PROTEIN CLASSIFICATION BASED ON SHAPE
1. Fibrous 2. Globular 3. Membrane FIBROUS PROTEIN
- A fibrous protein is a protein whose molecules have an elongated shape with one dimension much longer than the others.
- Simple, regular, linear structures
- There is a tendency to aggregate together to form macromolecular structures
- WATER-INSOLUBLE
- Most abundant in the body
- Most abundant in total mass GLOBULAR PROTEIN
- A globular protein is a protein whose molecules have peptide chains that are folded into spherical or globular shapes.
- The folding in such proteins is such that most of the amino acids with hydrophobic side chains (nonpolar R groups) are in the interior of the molecule and most of the hydrophilic side chains (polar R groups) are on the outside of the molecule.
- Generally, globular proteins are WATER- SOLUBLE substances.
- Have many kinds MEMBRANE PROTEIN
- A membrane protein is a protein that is found associated with a membrane system of a cell.
- Opposite of globular proteins: THEY ARE FOUND OUTWARD
- HYDROPHOBIC – WATER-INSOLUBLE
- Have fewer amino acids than globular
- Fibrous proteins are generally water-insoluble, whereas globular proteins dissolve in water. This enables globular proteins to travel through the blood and other body fluids to sites where their activity is needed.
- Fibrous proteins usually have a single type of secondary structure, whereas globular proteins often contain several types of secondary structure.
- Fibrous proteins generally have structural functions that provide support and external protection, whereas globular proteins are involved in metabolic chemistry, performing functions such as catalysis, transport, and regulation.
- The number of different kinds of globular protein far exceeds the number of different kinds of fibrous protein. However, because the most abundant proteins in the human body are fibrous proteins rather than globular proteins, the total mass of fibrous proteins present exceeds the total mass of globular proteins present.
a KERATIN - Fibrous protein - Abundant in nature - Found in protective coatings of an organism
- Major protein constituent of hair, feathers, wool, fingernails and toenails, claws, scales, horns, turtle shells, quills, and hooves.
- Hard keratins – have more disulfide bridges
- Soft proteins – have less disulfide bridges
- All attractive forces in secondary and tertiary structure interactions are involved a helix > 2 a helices > 4 photofilament > microfilament > and so on > keratin strength
COLLAGEN
- The most abundant of all proteins in humans (30% of total body protein),
- A major structural material in tendons, ligaments, blood vessels, and skin; it is also the organic component of bones and teeth.
- Triple helix – when three chains of amino acids wrap around each other to give a ropelike arrangement of polypeptide chains; due to the cyclic nature of proline (20% of collagen)
- Very long, thin, and rigid.
- Many such molecules, lined up alongside each other, combine to make collagen fibrils. Cross-linking between helices gives the fibrils extra strength.
- More cross linking = more rigidity = ageing/tanning
HEMOGLOBIN
Transports oxygen from the lungs to the tissues
141 a & 146 b ; 574 amino acids
It is a tetramer (four peptide chains) with each subunit also containing a heme group, the entity that binds oxygen.
Fetal hemoglobin (HBA) – dominant when in fetus; gets converted due to Oxidation
Adult hemoglobin – increases as we grow old
With four heme groups present, a hemoglobin molecule can transport four oxygen molecules at the same time.
Fe interacts with O
Beta globin chain
- (normal chain) Gly-Glu-Gly – Gly is polar acidic (capable of oxidizing)
- (abnormal: sickle cell anemia) Gly-Val-Gly
- Val is nonpolar (cannot oxidize)
- This is an example of substitution/cell mutation, causing different characteristics/functionality
- Has an effect to the conversion of Fetal hemoglobin into Adult hemoglobin because oxidation is needed; it cannot happen if there is valine since it cannot oxidize thus manifesting sickle cell anemia
- Oxygen has no slot to attach in the cell if Val is present = result: O2 cannot be transported
- Manifestation of sickle cell anemia: Madaling hingalin
MYOGLOBIN
- Globular
- Stores oxygen in muscles
- Monomer
- Consists of a single peptide chain and a heme unit, and hemoglobin has four peptide chains and four heme units
- Only 2 O2 can be stored
PROTEIN CLASSIFICATION BASED ON FUNCTION
The functional versatility of proteins stems from (1) their ability to bind small molecules specifically and strongly to themselves (2) their ability to bind other proteins, often other like proteins, to form fiber-like structures and
the assembly of collagen triple helices into more complex aggregations called collagen fibrils.
- Becomes GELATIN (water-soluble) when boiled in water — denaturation and hydrolysis
IMMUNOGLOBULIN (ANTIBODIES)
- A glycoprotein produced by an organism as a protective response to the invasion of microorganisms or foreign molecules.
- <tips= (upper-most part) of the Y structure: where the interaction with an antigen occurs
- Hydrophobic interactions, dipole–dipole interactions, and hydrogen bonds rather than covalent bonds.
- AIDS – upsets the body’s normal production of immunoglobulins and leaves the body susceptible to what would otherwise not be debilitating and deadly infections.
- ORGAN TRANSPLANT – use of drug suppressants for immunoglobulin production.
- Cyclosporine – best known <antirejection= drug
- BREASTFEEDING – passing of mother’s immunoglobulins to child via milk.
Basic structure:
Four polypeptide chains are present: two identical heavy (H) chains and two identical light (L) chains.
The H chains, which usually contain 400–500 amino acid residues, are approximately twice as long as the L chains.
Both the H and L chains have constant and variable regions. The constant regions have the same amino acid sequence from immunoglobulin to immunoglobulin, and the variable regions have a different amino acid sequence in each immunoglobulin.
The carbohydrate content of various immunoglobulins varies from 1% to 12% by mass.
The secondary and tertiary structures are similar for all immunoglobulins. They involve a Y-shaped conformation (Figure 20) with disulfide linkages between H and L chains stabilizing the structure.
LIPOPROTEINS - A lipoprotein is a conjugated protein that contains lipids in addition to amino acids. - Major function: to help suspend lipids and transport them through the bloodstream.
PLASMA LIPOPROTEINS
- A plasma lipoprotein is a lipoprotein that is involved in the transport system for lipids in the bloodstream.
- These proteins have a spherical structure that involves a central core of lipid material (triacylglycerols and cholesterol esters) surrounded by a shell (membrane structure) of phospholipids, cholesterol, and proteins.
- In the blood, cholesterol exists primarily in the form of cholesterol esters formed from the esterification of cholesterol’s hydroxyl group with a fatty acid.
- POLAR EXTERIOR — NONPOLAR INTERIOR
- HIGH PROTEINS & LIPIDS = HIGH DENSITY
4 MAJOR CLASSES OF PLASMA LIPOPROTEINS
1. CHYLOMICRONS
- Function: to transport dietary triacylglycerols from the intestine to the liver and to adipose tissue.
2. VERY-LOW-DENSITY LIPOPROTEINS (VLDL) - Function: to transport triacylglycerols synthesized in the liver to adipose tissue.
3. LOW-DENSITY LIPOPROTEINS (LDL) - Function: to transport cholesterol synthesized in the liver to cells throughout the body.
4. HIGH-DENSITY LIPOPROTEINS (HDL)
- Function: to collect excess cholesterol from body tissues and transport it back to the liver for degradation to bile acids.
Proteins Reviewer
Course: Medical Technology (MD)
University: Our Lady of Fatima University
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