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Chapter 3

Chapter 3 Carbohydrates.pdf

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Department
Life Sciences
Course
LIFESCI 2N03
Professor
Erin Westman
Semester
Fall

Description
Pryanose    o  btw  c1  c5   Carbohydrate chemistry - include sugars, starches andfiber. “-ose”name . - Most important sugars are hexose o Glucose fructose and galactose Monosaccharaides - onesugar - hexose 6 carbons have the same chemical formula   C H 6 (i12mer6differencesare thearrangement of Epimer    -­‐different  at  1  positions   atoms in space andinrelation totherest of the molecule :structure have different function Furctose       -­‐  Four  carbon  ring   Glucose   -­‐  very  sweet  main  sugar  in  fruits  and  honey   -­‐  6  carbon  ring   -­‐  frequently  added  to  processed  food  :  high  diertary  source   -­‐  somewhat  sweet   -­‐  most  common  and  important  to  nutrient     Galactose     (transported  around  the  body)   -­‐  least  common,  not  very  sweet     Disaccharides     Complex  sugars :  disaccharides  and   polysaccharides     -­‐ still  have  the  “-­‐ose”  ending  but  you  need  to  know     they  contain  2  sugars     o Maltose    (two  glucose)  produce  during  start   Condensation   digestions     -­‐ join  together  simple  sugars   o Sucrose  (glucose  +  fructose)  table  sugar  and   -­‐ makes  water    and  a  glycosidic  bond.     sweet  taste     Polysaccharides     o Lactose  (glucose  +glactose)  main  sugar  in     Glycogen     -­‐ found  in  meats  and  not  so  much  plants,  not  significant  source  of  carbohydrates     -­‐ role  is  to  store  glucose  for  future  use  in  the  liver  (can  be  found  in  the  muscle)     -­‐ Highly  branched  chains  that  enzymes  respond  by  attacking  them  for  glucose.   Starches     -­‐ plants  cell  store  glucose  as  starches     -­‐ long  branch  (un)branched  chains  linked  together     -­‐ packed  side  by  side  in  grains/wheat/rice/potatoes/legumes     -­‐ amylyopectin  (branched)  or  amylose(unbranched)     -­‐ enzymes  break  down  it  to  maltose  then  glucose/  “resistant  starch”  –  hard  to  digest   Fiber   -­‐ sugars  (polymers  of  glucose)  join  by  bonds  that  can’t  be  digested  by  humans   -­‐  Starch:  got  glucose  bond  that  can  be  digested  because  it  is  water  -­‐  soluble  fibers,  form  gels  (viscous)  and   easily  digested  by  bacteria  (fermentable).  Example:  corn  oats  barley  legumes  citrus  fruits.   -­‐ Cellulose:  got  glucose  bonds  that  cannot  be  digested  because  it  is  insoluble  fibers  that  do  not  form  gel  and   less  fermented.  But  it  can  promote  bowel  movement  alleviate  constipation  and  prevent  diverticular   disease.   Note  bacteria  and  humans  shows  benefit:  mutralism.     Dietary  fibre:     -­‐ associated  with  phytic  acid  (pytate  which  is  not  good  because  it  get  excreted)     -­‐ not  a  dietary  fiber  but  found  in  the  some  foods   -­‐ uncertain  if  fiber  itself  or  phytate  is  the  cause  of       o bind  ingested  minerals  ;  which  are  then  excreted  as  an  insoluble  complex   o excessive  (>40g/day)  fiber  intake  could  risk  of  micronutrients  deficiencies  because  it  robs  you  of   the  essential  nutrients  that  you  should    be  eating.     Carbohydrate  hydrolysis     Water  and  a  larger  sugar  makes  two  smaller  sugars  by  breaking  the  bonds  and  water.       Carbohydrate  Digestions   Steps:     -­‐ Initiates  in  the  mouth  :  salivary  amylase  hydrolyzes  starched  to  dextrins  (shorter  polysacchardies)     -­‐ Pauses  in  the  stomach:    HCL  and  protease  cause  the  inactive  salivary  amylase  also  the  fibre  lingers  in  the   stomach  to  signals  fullness   -­‐ Resumes  in  the  small  intestine:  pancreatic  amylase  does  MAJOR  part  of  hydrolyzing  starch/dextrins  to   maltose.   o Inside  the  intestine:  the  outer  membrane  of  the  cell  the  enzymes  break  down  disaccharides  .   Carbohydrate  Absorption   Small  intestine:   -­‐ Glucose   o Absorbed  by  active  transport  in  the  small  intestine  ,   and  some  in  mouth  lining     -­‐ galactose     o absorbed  by  active  transport,     -­‐ fructose   o  absorbed  facilitated  diffusion  which  is  very  slow.  Since  its  slow  it  doesn’t  immediately  affect  blood   sugar.      (also  amylose  because  there’s  a  certain  start  region)   Large  intestine:   -­‐ fibres     o remain  undigested  and  unabsorbed  in  the  small  intestine    to  the  large  intestine     o bacteria  in  the  large  intestine  ferment  some  fibres  :  generate  water,  gas  and  short  chain  fatty  acid   o cells  of  the  colon  absorb  and  use  these  short-­‐cain  fatty  acid  :  little  energy  is  generated  by  fiber     -­‐ attracted  water  to  soften  stools     Lactose  Intolerance     -­‐ symptoms  after  lactose-­‐containing  food:  bloating,  gases,  cramping,  and  diarrhea     -­‐ caused  by  low  or  absent  lactase  enzymes  on  intestinal  cell  membrane  –  the  enzymes  cannot  cleave  the   bond  of  the  lactose  sugar,  therefore  the  bacteria  ferments  the  lactose  and  produces  gasses.     o we  are  mammals:  lactase  expression  is  highest  right  after  birth  so  infants  feed  on  milk  effetely     o genetic  regulation  of  lac  operon  may  decrease  expression  of  lactase  to  5-­‐10%  by  teenage  years     o also  difference  in  ethic  groups  because  of  the  food  and  sugar  that  was  prepared  in  their  food   (culture.)       Living  without  lactase   -­‐ avoid  food  high  in  lactase:  milk  is  high  in  lactose  while  femented  foods  (cheese/soy  milk)  lower  in  lactose   because  the  bacteria  already  hydrolyzed  it,  must  meet  RDA  (riboflavin  vitamin  D  and  calcium)     -­‐ Pre-­‐treated  milk  with  lactase  enzymes  :  hydrolyze  lactose  before  consumptions     -­‐ Ingest  lactase  tablets  with  dairy  fiids  :  hydrolyze  lactose  but  must  make  it  through  the  stomach   Role  of  glucose   -­‐ cell  use  glucose  for   energy  (mostly   starched)     -­‐ cells  modify   structures  with   carbohydrates  (   glycoproteins  =  sugar   +  protein  or   glycolipids  =sugar  +   Or  epinephrine   fats)     -­‐ stored  as  glycogen  or   use  to  make  fat     -­‐ prevent  ketosis   (require  about  50-­‐ 100  g  carb  /day     Blood  glucose  homeostasis     -­‐ any  extreme  blood  sugar  level  is  detrimental     o low  blood  sugar    cause  dizziness  and  hypoglycemia     o high  blood  sugar  cause  fatigue  and  diabetes     -­‐ regulated  by  hormones  from  pancreases     o insulin  (beta  cells  of  pancreas):  signals  to  move  glucose  from  the  blood  into  tissue-­‐    for  storage     o glucagon  (alpha  cells  of  pancreas):  signals  to  move  glucose  out  of  the  storage  and  into  the  blood   streams  (  to  supply  tissue)     Insulin   Glucagon   -­‐ secreted  in  response  to  high  blood  sugar   -­‐ secreted  in  response  to  low  blood  sugar   -­‐ amount  proportional  to  the  deviation  from   -­‐ direct  liver  to  break  down  glycogen  and  release   normal  blood  sugar   glucose  to  the  blood   o muscle  tissue  does  not  react  to  glucagon;  the   -­‐ insulin  receptors  on  various  tissue   stimulates  the  uptake  of  glucose  into  the   muscle  glycogen  is  for  cell’s  own  use     cells     -­‐ as  blood  glucose  rises  to  normal  secretions  of   o some  cells  just  take  little  for  their   glucagon  slow  and  then  stops     use     o cells  of  liver  and  muscles  take  up   Epinephrine  =  adrenaline     -­‐ hormone  secreted  by  adrenal  gland  in  response  to   and  store  as  glycogen     stress     -­‐ As  glucose  in  the  blood  is  depleted  by  cells   up  taking  it,  insulin  secretion  lows  down   o fight  or  flight:  signals  for  glucose  to  release     and  stop  as  blood  sugar  reach  normal.       which  prepares  for  muscle  action  or  a  run  for   -­‐ Founded  by  sir  Frederick  Banting  &   it.   Charles  Herbert  best     -­‐ also  signal  liver  to  release  glucose  from  glycogen   Blood  sugar  disease   Diabetes:  They  have  blood  sugar  even  when  fasting  (greater  than  7  mmol/L)  Two  types;  Type  1:  pancreas  fails  to   produce  insulin  (uncommon)  Type  2:  cells  fail  to  respond  to  insulin  (common  associated  with  obesity).  There  is  also   gestational  diabetes  which  is  temporary  during  pregnancy.       Hypoglycemia:  They  have  low  blood  sugar  causing  weakness,  fainting(  due  to  lack  of  glucose  for  brain  and  nervous   system).  This  is  often  due  to  poorly  managed  diabetes  (  too  much  insulin/activity/poor  food  intake/illness  .  Treated   by  modifying  the  diet  to  include  more  fibre  –rich  food  and  adequate  protein  (smaller  meals  more  frequently)   Glycemic  Response :  the  extent  to  which  a  food  raises  the  blood  glucose  concentration  and  elicits  an  insulin   response     -­‐ measure  how  quickly  blood  sugar  rises,  how  high  it  release  and  how  quickly  it  returns  to  normal   -­‐ low  response:  slow  absorption,  modest  rise  in  blood  glucose,  smooth  return  to  normal    (resistant  startch)   -­‐ high  response:  fast  absorption  and  surge  in  blood  glucose,  overreaction  that  plunges  glucose  below  normal   are  less  desirable.  (refine  sugar)     Medium:  whole  grain   Low:  legumes  and  milk   and  fruits   products     High:  Refine  sugar  and     Process  foods     Glycemic  index  applications   -­‐ people  with  diabetes  :  limit  high   Nutritional  sugar  sources     glycemic  index  choices  help  stabilize   Natur
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