proteins/amino acids

• Protein


  Organic macronutrient with caloric value of 4 kcals/g
• The Chemist's View of Proteins

  • Atoms: carbon, hydrogen, oxygen, nitrogen
  • Amino acids: carbon, hydrogen, amino group, acid group, side group/chain

  
• Proteins are more complex than carbohydrates or fats
• Twenty amino acids


  • Acidic
  • Basic
  • Aromatic
  • Ketogenic
  • Glucogenic

  
• Non-essential amino acids


  • alanine
  • arginine
  • asparagine
  • aspartic acid
  • cysteine
  • glutamic acid
  • glutamine
  • glycine
  • proline
  • serine
  • tyrosine

  
• Amino Acid Metabolism


  1. Anabolism: neurotransmitters, unique compounds, semi-essential AA, body fat

  2. Catabolism: [ATP]intracellular
• Amino Acid Hierarchy


  • Cysteine (semi-essential)
  • Methionine
  • Tyrosine (semi-essential)
  • Phenylalanine

  
• Essential Amino Acids


  • Histidine
  • Isoleucine
  • Leucine
  • Lysine
  • Methionine
  • Phenylalanine
  • Threonine
  • Tryptophan
  • Valine

  
• Proteins are made up of amino acids linked by peptide bonds formed through condensation reactions
• Protein Structure


  1. Primary

  2. Secondary

  3. Tertiary

  4. Quaternary
• Condensation reactions link amino acids to form proteins

  
• Pyruvate is the carbon skeleton of the amino acid alanine

  
• Protein Denaturation


  Disruption of stability, uncoiling and loss of shape, caused by stomach acid
• Protein Digestion


  1. Mouth

  2. Stomach: hydrochloric acid, pepsinogen to pepsin

  3. Small intestine

  
• Protein Absorption


  Transport into intestinal cells, uses of amino acids by body, blood transport amino acids to liver, enzyme digestion, predigested proteins
• Protein Synthesis


  1. DNA template to make mRNA (transcription)

  2. mRNA carries code to ribosome

  3. mRNA specifies sequence of amino acids (translation)

  4. tRNA delivers amino acids to ribosome, enzymes catalyze amino acid bonding, multiple ribosomes working

  
• mRNA Function


  Transcribe DNA code, take code to ribosome, give instructions to ribosome on how to build protein

  
• tRNA Function


  Deliver amino acids to the ribosome as it is building (synthesizing) protein

  
• Protein turnover


  Reason why we need to synthesize protein
• Functions/roles of protein in the body

  • Growth (children) and maintenance (adults)
  • Structures - Building blocks for most body structures
  • Replacement of dead or damaged cells
  • Consider all the proteins in / make up a cell
• Enzyme catalysis


  1. Substrate attraction to active site

  2. Enzyme forms complex with substrates

  3. Enzyme unchanged, new compound formed
• Enzymes


  Breakdown, build, transform, catalyze
• Roles of proteins


  • Hormones - Insulin, growth hormone
  • Neurotransmitters - Epinephrine, Norepinephrine, Serotonin
  • Other unique molecules - thyroxin, melanin, niacin
• Protein in cells and plasma

  Regulates fluid balance - "leaky" blood vessels can lead to edema
• Causes of edema


  • Excessive protein losses - inflammation, illness
  • Inadequate protein synthesis - liver damage
  • Inadequate protein intake
• Proteins as buffers


  Attract hydrogen ions to regulate acid-base balance
• Protein transport functions


  • Lipid - lipoproteins
  • Vitamin binding proteins
  • Hemoglobin
  • Mineral binding and storage protein
  • Pumps - Na+/K+
• Antibodies


  Defend body against disease, have specificity, provide immunity and memory
• Protein for energy and glucose


  Starvation and insufficient carbohydrate intake leads to wasting of lean body tissue
• Protein metabolism


  Key reactions - Transamination, Deamination, Converted to urea
• Making non-essential amino acids

  Key reactions

  
• Breaking down nutrients for energy - Amino acids

  1. Deamination of amino acids

  2. Amino acids converted to pyruvate, acetyl CoA, or enter TCA cycle

  
• Urea


  How the body gets rid of ammonia
• Factors affecting protein quality

  • Amino acid composition
  • Digestibility
• Biological value


  Nitrogen retained / Nitrogen absorbed
• Amino acid (chemical) score

  Essential amino acid in test protein / Essential amino acid in reference protein
• Protein digested-corrected amino acid score (PDCAAS)

  Chemical score x Digestibility
• High-quality proteins


  • Animal proteins
  • Plant proteins
• Complementary proteins


  Low-quality proteins combined to provide adequate levels of essential amino acids
• Protein claims on food labels

  • Quantity of protein in grams
  • Percent Daily Value (not mandatory, but should be given)
  • Protein claim
  • Intended to consume by children younger than 4 years
  • If % DV given, then it should indicate the quality too