Lecture 8 - Proteins Flashcards
What is the 21st AA in humans that is not apart of the standard 20
selenocysteine
In humans, how many proteinogenic AAs are there
21
What is a proteinogenic AA
AA incorporated into protein during translation
What is an example of a non-proteinogenic AA
GABA (some neurotransmitters)
How many AAs are essential
9
What does it mean to be an essential AA
body cannot make it, must come from diet
What is the newest addition to the essential amino acids
histidine
What types of tissues have protein in the body
adipose tissue, blood, connective tissue, eye lens, skeletal muscle, cortical bone, and skin
What are the 3 main tissues in the body for protein location
blood (RBC), connective tissue, and the eye lens
What are enantiomers
D & L configurations, mirror images of one another
What are zwitterions
H transferred from COOH to NH2 in AA structure to make a negative COO- and positive NH3+, making a more polar structure
AAs are connected by ____________ bonds
peptide bonds
What is another term for peptide bond
amide bond
How do 2 AAs bond
carboxyl end of one reacts with amino group of another, releasing H2O as condensation and forming a peptide bond
What is the difference between the term polypeptide and protein
polypeptide = >50 AAs (long chain of amino acids)
more than 1 polypeptide = biologically active protein
What is primary structure
polypeptide chain of AAs held together by peptide bonds
What is secondary structure
hydrogen bonds that create a more stable structure of the polypeptide chain (think alpha helix and beta sheets)
What is tertiary structure
arrangement of secondary structure in 3D space
What is quaternary structure
combination of 2 or more tertiary structures required to make a functional protein
What is a native protein
normal 3D structure conformation
What is denatured protein
loss of bioactivity and conformation via pH, heat, detergents, etc.
What level of structure is not affected by denaturation
primary structure
What is a conditionally essential AA
not normally required in the diet in a healthy individual, but essential under certain contexts
What is an example of a genetic problem (from birth) that would result in a conditionally essential AA being essential
phenylketonuria: person is unable to breakdown Phe into Tyr (build up of Phe in the body causes mental defect)
What is a developed disease that would result in a conditionally essential AA being essential
liver disease that impairs Phe and Met catabolism (Tyr and Cys are synthesized from Phe and Met, so here Tyr and Cys are indispensable)
What are non-essential AAs
not needed in diet, completely synthesized in the body
What are 3 basic AAs
lysine, arginine, histidine
What are the characteristics of the basic AAs
polar
+ve charge on NH3 group enabling DNA binding
What are the characteristics of lysine
essential
simple straight chain
absent from grain products
What are the characteristics of arginine
non essential in healthy adults
What are characteristics of histidine
essential
ring structure
used to produce histamine
What are the 4 acidic AAs
aspartate, glutamate, asparagine, and glutamine
What are the characteristics of acidic AAs
polar
-ve charge on carboxyl side chain
What are the characteristics of aspartate
non-essential
transmitted to oxaloacetate (Krebs)
What are the characteristics of glutamate
non-essential
transmitted to a-ketogluterate (Krebs)
used to produce GABA
What are the characteristics of asparagine
non-essential
What are the characteristics of glutamine
non-essential
important in AA catabolism because it is a carrier of nitrogen
What are the neutral AAs
glycine and alanine
What are the characteristics of the neutral AAs
no charge, non-polar, aliphatic (C and H atoms join in straight or branched chains)
What are the characteristics of glycine
non-essential
no enantiomers
used primarily to produce porphorin
What are the characteristics of alanine
non-essential
important in AA catabolism because it is a carrier of nitrogen
important role in the glucose-alanine cycle
What are some branched chain AAs
leucine, isoleucine, and valine
What are the characteristics of branched chain AAs
neutral aliphatic, non-polar, all are branched, all are essential, not catabolized in the liver (high levels found in ciruclation)
What AAs are found in high amounts in circulation and why
branched chain: not catabolized in liver, so lots is found in circulation
What are the hydroxylated AAs
serine and threonine
What are the characteristics of hydroxylated AAs
OH group on side chain is important for protein phosphorylation
polar
What are the characteristics of serine
non-essential
OH group on side chain important for phosphorylation
What are the characteristics of threonine
essential
OH group on side chain important for phosphorylation
What are sulphur containing AAs
cysteine and methionine
What are the characteristics of sulphur containing AAs
contain sulphur
non polar
What are the characteristics of cysteine
non-essential
made from methionine
“spares” methionine when cysteine is consumed in the diet
used to form disulphide bonds
used in glutathione synthesis
What are the characteristics of methionine
essential
methionine is limiting in legumes
What are aromatic AAs
phenylalanine, tyrosine, tryptophan, and proline
What are the characteristics of aromatic AAs
contain rings
non polar (except tyrosine)
What are the characteristics of phenylalanine
essential
used to make tyrosine
What are the characteristics of tyrosine
non-essential
“spares” Phe
used to synthesize neurotransmitters
What are the characteristics of tryptophan
essential
used to make serotonin
used for niacin synthesis
What are the characteristics of proline
non-essential
important for collagen production
aliphatic side chain
What are the 9 essential amino acids
lysine, histidine, leucine, isoleucine, valine, threonine, methionine, phenylalanine, and tryptophan
Is there enzymatic break down of proteins in the mouth during digestion
no
What breaks down proteins in the stomach
HCl in gastric juice
pepsin
What does the pancreas have to do with protein break down
pancreatic juice used to digest proteins enzymatically
What breaks down proteins in the small intestine
enzymes break down proteins, zymogens are active, and AAs are absorbed
What cells secrete HCl in protein digestion in stomach
parietal cells
What are the two functions of HCl
denature proteins
activate pepsin
What bonds are disrupted in denaturing of protein
hydrogen bonds
electrostatic bonds
Pepsin is secreted as _________________, which is an inactive zymogen
pepsinogen
How does pepsinogen activate in HCl
since HCl is acidic, pepsinogen can activate as pepsin via conformational change (cannot do this in neutral pH)
What is meant by pepsin is an endopeptidase
cleaves peptide bonds within a polypeptide chain
What activates trypsinogen to trypsin in the small intestine
enteropeptidase enzyme in the brush border
Activation of trypsin activates what other enzymes
chymotrypsin
elastase
carboxypeptidase
What two ways are AAs absorbed in the small intestine
facilitated diffusion
active transport
What are absorbed faster, essential or non essential AAs
essential
Do free AAs have advantage for absorption over protein from foods
no
What happens to proteins in terms of use
used for energy or synthesis of new proteins
What is the function of glutamine in intestinal enterocytes
generate energy for the cell
stimulate cell proliferation
increase synthesis of heat shock proteins
drive mucus production
Liver uses 20% of AAs to…
make new protiens/enzymes and make peptide hormones
Liver uses 80% of AAs to…
catabolize them so NH3 is sent to urea cycle, carbon skeleton sent to Krebs for energy
What are the 4 aspects to consider in protein quality
AA composition
digestibility
presence of toxic factors
species consuming the protein
