Slide Set 12: Milk Protein Biosynthesis Flashcards
How many amino acids are found in milk?
18
Where is the milk protein synthesized?
in the ribosome of the RER of the mammary epithelial cell from amino acids
What are the major proteins that are only found in milk
- casein proteins
- lactoglobulins: b-lactoglobulin (50% of whey protein)
- lactalbumins: a-lactalbumin (25% of whey protein)
Which membrane do the amino acids go through to enter the cell?
basal membrane
What do most of amino acid the transport systems depend on?
Na
What are the classes of amino acid transport systems?
- Neutral group
- Cationic group
- Anionic group
What are the three main systems of neutral group transport system?
ASC (named after Alanine, Serine, Cysteine)
A (named after Alanine)
L (named after Leucine)
What is the cationic transport system?
Y + (named after Lys and Arg) - preference for positively charged side chains
What is the anionic transport system?
- (named after for Asp and Glu) preference for negatively charged side chains
Which transport systems are not Na-dependent?
L neutral and Y+
Which amino acid is the most abundant in milk?
Glutamine
What are the two phases of amino acid utilization by mammary gland?
- cellular uptake of amino acids
2. intracellular metabolism of amino acids
Uptake of amino acids by mammary gland depends on:
- Arterial concentration of amino acids
- Rate of mammary blood flow
- Uptake rate of amino acids by mammary gland
What are the fate of amino acids in mammary cell?
- Undergo RNA directed polymerization to form milk protein
- Be retained in the mammary cell in the form structural protein or enzymes
- Be used as source of carbon and nitrogen for synthesis of other amino acids
- Pass unchanged into milk, blood or lymph
How can amino acid uptake by the mammary cell be quantified?
by measuring arterio-venous (AV) amino acid difference
How much essential amino acids are absorbed?
in amount adequate to provide their milk protein residuals
Essential amino acids taken by the mammary gland can be divided into two groups:
- EAA taken up in excess of their milk residuals (arg, BCAA)
- EAA taken up stiometrically (1:1) (met, phe, typ)
Which amino acid is taken up the most amount?
methionine
What are the requirements for milk protein biosynthesis?
ribosome
mRNA
tRNA
ATP
What are the three steps of milk protein biosynthesis?
- Transcription
- Activation
- Translation
Explain the transcription step of milk protein biosynthesis?
- mRNA is formed from DNA
- mRNA carries the genetic code of specific protein
- mRNA locates itself in the ribosome
Explain the activation step of milk protein biosynthesis
- AA in the cytoplasm activated by ATP
- Activated AA attached to tRNA
- tRNA are specific for each amino acid
Explain the translation step of milk protein biosynthesis
- Takes place in the ribosome
- Anticodon in tRNA recognizes the codon in mRNA for specific amino acid
- AA released form tRNA and joins the polypeptide chain.
Free amino acids from the blood are not the only sources of amino acids for protein synthesis. What are some other sources?
- AA derived from degradation of cellular protein
- AA derived from degradation of intracellular protein (e.g. degradation of caseins)
Why does transamination occur?
Some NEAA are synthesized in the mammary gland from other amino acids
What results in allergic reactions?
Undigested or partially digested large protein molecules may act as antigens and result in allergic reactions
What are the symptoms of milk allergies?
nausea
vomiting
diarrhea
intestinal inflammation
What is the incidence of milk allergy?
0.5 to 7.5%
What is the cause of milk allergy?
B-lactoglobulin
