BIOL 380 Lecture Notes - Lecture 5: Essential Amino Acid, Phenylalanine, Phenylketonuria
26 May 2018
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BIOL 380 – Lecture 5 – Proteins
- Proteins: large, complex molecules found in cells of all living things
- dictated by genetic material (DNA)
- Contain carbon, hydrogen, oxygen and nitrogen (major source of nitrogen in the body)
- Made from 20 different amino acids
- Energy content: 4cal/g
- Amino acids – molecules composed of a
central carbon atom connected to 4 other
groups: an amine group, an acid group, a
hydrogen atom, and a side chain.
Amino acids
- Essential amino acids
o Cannot be produced by our bodies
o Must be obtained from food
- Nonessential amino acids
o Can be made by our bodies (generated by essential amino acids)
o Made by transferring amino groups (transamination) onto ketoacids
- Conditionally essential amino acids
o Must be obtained from diet under certain conditions such as for infants, seniors and
someone suffering from ailments
o E.g. disease phenylketonuria (PKU) – cannot
metabolize phenylalanine. Normally, the body
uses phenylalanine to produce the non-essential
amino acid tyrosine, so the inability to metabolize
phenylalanine results in failure to make tyrosine.
Tyrosine becomes a conditionally essential amino
acid.
Conditionally
essential amino acids
- Tyrosine (made from phenylalanine) is
conditionally essential in people suffering from
phenylketonuria
- Glycine synthesis requires folate
- Cysteine is made from methionine which is
limiting in unbalanced vegetarian diets
* focus on learning the pathologies associated with
a deficiency in one of the essential amino acids (aka
know the ones we discuss individually)
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2
some important amino acids
1. Glycine and glutamine are
nitrogen donors for heme and
bile, and nucleotide synthesis,
respectively
2. Leucine (ketogenic amino acid) →
used for fatty acid synthesis (via
acetyl coA)
3. Alanine (glucogenic amino acid)
→ used for glucose synthesis
(gluconeogenesis)
4. Glutamate, tryptophan, tyrosine
and arginine: are modified into
neurotransmitters; GABA (gama
amino butyric acid), serotonin,
dopamine and nitric oxide
respectively
5. Lysine and methionine are precursors of carnitine that transports lipids into mitochondria
6. Tyrosine is modified into thyroid hormones
7. Arginine is the main precursor of urea
How are proteins made?
- Proteins are long chains of amino acids
- Peptide bonds join amino acids together
- When two amino
acids join together, the
amine group of one binds
to the acid group of another
via a peptide bond. A
molecule of water is
released
- Gene expression is the process by which cells use genes to make
proteins
o Gene: segment of deoxyribonucleic acid (DNA) that
serves as a template for the synthesis (expression) of a
particular protein
- Transcription: messenger RNA copies the genetic information
from DNA
- Translation: the genetic information in RNA is converted into the
amino acid sequence of a protein
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Protein turnover
- Existing proteins are degraded to provide the
building blocks for new proteins
- Amino acid pool includes amino acids from
food and cellular breakdown
- Anabolic = building up
Amino acid pool
- Healthy body = stable pool of amino acid
- Protein degradation = protein synthesis
- Dietary protein intake makes up for oxidized
amino acids or amino acids used in other
pathways
Protein organization
- Protein organization
determines its function
1. Sequential order of the amino acids = primary structure
2. Spiral shape from twists = secondary structure (hydrogen bonds &
disulfide bridges)
3. Folds and loops – unique 3D shape = tertiary structure
4. Combination of more than one strand/subunit = quatenary structure
* protein shape determines function (think hemoglobin, RBC)
- Denaturation : proteins can uncoil and lose their shape when they are
exposed to heat, acids, bases, heavy metals, alcohol, and other damaging
substances
Protein diet
- For protein synthesis, all essential amino acids must be available to the cell
o Incomplete protein (low quality): insufficient essential amino acids → does not support
growth and health
o Complete protein (high quality): sufficient amount of all nine essential amino acids →
derived from animal and soy protein
o Complementary proteins: 2 or more foods are combined to supply all 9 essential amino
acids for a complete protein
Protein digestion
- Protein digestion begins in the stomach
o Hydrochloric acid denatures protein strands and activates pepsin
o Pepsin is an enzyme that breaks down proteins into short polypeptides
- Gastrin is a hormone that controls hydrochloric acid production and pepsin release
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Proteins: large, complex molecules found in cells of all living things. Contain carbon, hydrogen, oxygen and nitrogen (major source of nitrogen in the body) Amino acids molecules composed of a. Energy content: 4cal/g central carbon atom connected to 4 other groups: an amine group, an acid group, a hydrogen atom, and a side chain. Essential amino acids: cannot be produced by our bodies, must be obtained from food. Nonessential amino acids: can be made by our bodies (generated by essential amino acids, made by transferring amino groups (transamination) onto ketoacids. Conditionally essential amino acids: must be obtained from diet under certain conditions such as for infants, seniors and someone suffering from ailments, e. g. disease phenylketonuria (pku) cannot metabolize phenylalanine. Normally, the body uses phenylalanine to produce the non-essential amino acid tyrosine, so the inability to metabolize phenylalanine results in failure to make tyrosine. Tyrosine (made from phenylalanine) is conditionally essential in people suffering from phenylketonuria.
