proteins
H,O,C, and N arranged as strands of amino acids
amino acids
the building blocks of proteins
amino acids differ in their side chains
how many amino acids
20
9 essential
amino acid side chains
differ in size, shape, and electrical charge
components of an amino acid
central carbon, amine group, acid group, and side chain
essential amino acids
can't be synthesized by the body or not enough is produced to meet physiological needs
without the essential nutrients, the body cannot make the proteins it needs to do its work
recycling amino acids
food proteins after digestion and body proteins after they are finished their cellular work are broken down for their component amino acids
these amino acids are raw materials for cells to build protein molecules
uses of recycled amino acids
used for energy, nitrogen discarded as waste, recycles something valuable while reducing the burden of disposing of nitrogen, can be an emergency fund in times of low fuel, glucose, or protein
peptide bond
bond that connects different amino acids, forming a link in a protein chain
essential amino acids
histidine
isoleucine
leucine
lysine
methionine
phenylalanine
threonine
tryptophan
valine
protein folding and coiling
caused by side chains attracting and repulsion from each other
the coil folds and flips over itself to take a functional shape
the different shapes allow proteins to perform different tasks
primary structure
the amino acid sequence
this determines the shape and shape determines function
secondary structure
coiling
alpha helixes and beta pleated sheets
tertiary structure
folding
formed by alpha helixes and beta sheets around each other
quaternary structure
arrangement of a multiple folded protein
ex: hemoglobin
sickle cell anemia
hemoglobin is abormal; mix-up with the sixth amino acid and it alters the proteins to be unable to carry and release oxygen
cells collapse into crescent shapes
can cause abnormal blood clotting, strokes, bouts of severe pain, susceptibility to infection,
gene expression
the nucleus contains DNA to product every human proteins but some genes are expressed and some are not;
some cells specialize in making certain proteins
denaturation
irreversible change in a protein's folded shape brought about by heat, acids, bases, alcohol, salts of heavy metals, etc.
ex: HCl in the stomach or cooking an egg
where does protein digestion begin
in the stomach
role of HCl
breaks down proteins in stomach and activates pepsin
uncoil the protein to allow pepsin to attack the peptide bonds
stomach lining
protected against attack by acid and enzymes by a coat of mucus secreted by its cells
digestion in small intestine
most proteins have been denatured into smaller pieces
alkaline juice from the pancreas neutralizes the acid; this allows the enzymes to complete the final breakdown of the protein strands
pepsin
enzyme in stomach that breaks down proteins into short polypeptides and amino acids to be taken to the small intestine
pancreatic enzymes
complete the digestion of proteins into di- and tripeptides and amino acids
brush border enzymes
enzymes within the intestinal lining that split the di- and tripeptides
amino acids after digestion of proteins
absorbed as single amino acids and released into the blood stream
carried to the liver to be used or released into the blood to be take up by other cells in the body
cells can link the amino acids together to make proteins to keep for their own or to go i
central dogma
DNA-->mRNA-->proteins
requirement for protein synthesis
ALL ESSENTIAL AMINO ACIDS must be present
sequence of a protein determined by:
genes
transcription
messenger RNA copies the genetic information from DNA
takes place in the nucleus
translation
genetic information in RNA is converted into the amino acids sequence of a protein
mRNA takes it outside of the nucleus for translation to occur
tRNA collects amino acids from the cell fluid and brings them to the mRNA
protein turnover
continuous breakdown and synthesis of body proteins involving the recycling of amino acids
majority of body's proteins found in
muscle tissue; allow the body to move and can release amino acids for energy if needed
affects shape and strength of bones, teeth, skin, tendons, cartilage, blood vessels, etc.
acid-base balance
proteins help maintain the acid-base balance of various body fluids by acting as buffers
antibodies
proteins form the immune system moelcules that fight diseases
blood clotting
proteins provide the netting on which blood clots are built
energy and glucose
proteins provide some fuel for the body's energy needs
enzymes
proteins facilitate needed chemical reactions
fluid and electrolyte balance
proteins help to maintain the water and mineral composition of various body fluids
gene expression
proteins associate and interact with DNA, regulating gene expression
hormones
proteins regulate body processes; some are proteins or are made from amino acids
transportation
proteins help transport needed substances (lipids, minerals, and oxygen) around the body
energy density of proteins
4 kcal/gram
amino acids to glucose
amino acids can be converted to glucose, fatty acids never can
amino acids therefore can maintain a blood glucose level
the nitrogen from the amine groups are stripped and incorporated into the liver as urea and excreted through the urine
three uses for oversupplied amino acids
amine groups discarded
residues can either meet immediate energy needs, make glucose for storage as glycogen, make fat for energy storage
storage of proteins
no storage center for proteins, excess must excrete the amine group and use the residues
therefore, during starvation proteins are taken from small proteins in the blood, then from tissues in muscles, liver, or other organs
four conditions for wasting amino acids
when body lacks energy from other sources
when diet supplies more protein than the body needs
when body has too much of a single amino acid (ex: from a supplement)
when diet supplies protein of low quality with too few essential amino acids
DRI intake for proteins
0.8 grams for each kilogram of body weight
1.8 grams/kilogram
1 kilogram=2.2 pounds
minimum amount is 10% of total calories and no higher than 35%
women: 46 grams per day men: 56 grams per day
nitrogen balance
amount of nitrogen consumed compared with the amount excreted in a given time period
this is the goal for healthy, non-pregnant adults (consume enough to replace what is used every day)
positive and negative nitrogen balance
more protein at the end of the day than they had at the beginning ex: growing children, pregnant women
losing more nitrogen than they are taking in ex: illness or injury triggers this, amino acids and energy are needed to fuel body's defenses and fight th
nitrogen equilibrium
intake and outtake of nitrogen are equivalent
this is desired
complete protein
supplies all essential amino acids
body must have all essential amino acids to build proteins; if one is missing the amino acids will be excreted
incomplete protein
low in 1 or more essential amino acid
complementary proteins
2 or more incomplete proteins; amino acid assortments complement each other in a way that essential amino acids missing from one are supplied by the other
must be eaten in the same day
ex: grains and legumes, seeds/nuts,and vegetables
excess proteins
create too much ammonia (NH3) and that stresses the kidneys
too much NH3=toxic
excess proteins=extra calories=extra fat
harms to a high protein diet
o Low in plant foods (fiber, vitamins, phytochemicals)
o Increase risk for heart disease
o Linked with colon cancer
o Stresses kidneys
o Increases bone loss
o Recommendation: no more than 2x RDA for protein
protein-energy malnutrition
world's most widespread malnutrition problem; includes both marasmus and kwashiorkor
prevalent in Africa, Central America, South America, Middle East, and East and South Asia
strikes early in childhood
marasmus
form of PEM related to protein malnutrition and infections with recognizable symptoms like edema
occurs most commonly in children from 6-18 months on a diet of low energy and low protein quality
top contributors of protein in the US
beef, poultry, milk
effects of marasmus
wasting and weakening of muscles, stunted brain development, slow metabolism, no fat under skin to insulate against cold, stunted growth, skin loses elasticity and moisture, digestive tract lining deteriorates and absorption fails, anemia, low immunity be
kwashiorkor
disease resulting from extremely low protein intake
symptoms resemble marasmus but without wasting of body fat
proteins and hormones to maintain fluid balance are gone and fluid leaks out of the blood and accumulates in the belly and legs causing edema
of
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