topic 3B - more exchange and transport systems Flashcards
what is digestion?
a process in which relatively large, insoluble biological molecules in food are hydrolysed into smaller, soluble molecules that can be absorbed across the cell membranes into the bloodstream and delivered to cells in the body
the role of enzymes in digestion:
enzymes are essential for the process of digestion as they catalyse the hydrolysis
what are the products of digestion used for?
-to provide cells with energy (via respiration)
-to build other molecules for cell growth, repair and function
protein + hydrolysation
amino acid
carbohydrates + hydrolysation
simple sugars
lipids + hydrolysation
glycerol and fatty acids
what does the human digestive system include?
-glands
-mouth
-oesophagus
-stomach
-small & large intenstines
-liver
the role of the mouth (digestive system)
-contains teeth which break food into smaller pieces and increase its surface area to volume ratio
-carbohydrate digestion begins here
-the food is shaped into a bolus (ball) by the tongue and lubricated in saliva so it can be swallowed easily
the role of the oesophagus
(digestive system)
-a hollow tube with muscular walls
-food passes from the mouth to the stomach (through this)
-contractions of the smooth muscle in the wall of the oesophagus help move food down towards the stomach
the role of the stomach
(digestive system)
protein digestion begins here
the role of small intestine
(digestive system)
-food passes through the lumen
-the wall of the small intestine contains smooth muscle tissue, which rhythmically contracts to move food along
-soluble food molecules are absorbed into the bloodstream across the wall of the small intestine (by diffusion and active transport → co transport)
-ileum is long and lined with finger-like villi to increase the surface area over which absorption can take place
-water absorption also occurs here
the role of the large intestine
(digestive system)
-any water remaining in food that was not able to be digested is absorbed here, along with vitamins and minerals
-undigested food material (faeces) is stored in the rectum and removed through the anus
enzymes in the digestive system:
-enzymes are substrate specific (different enzymes digest and breakdown the different biological molecules contained in food)
-digestive enzymes are extracellular
what are the three main types of digestive enzymes?
carbohydrases, proteases and lipases
where does the digestion of carbohydrates occurs?
in the mouth and the small intestine
what is amylase?
a carbohydrase that hydrolyses (breaks down) starch into maltose
what happens to maltose?
it is hydrolysed into glucose by the enzyme maltase
where is amylase made?
in the salivary glands, the pancreas and the small intestine
what is maltase?
a disaccharidase which is found in cell-surface membranes of the epithelial cells lining the small intestine
which other disaccharidases are in the cell-surface membrane of the epithelial cells in the small intestine and what do they do?
sucrase and lactase:
they hydrolyse sucrose and lactose respectively
this allows the absorption of monosaccharides into epithelial cells of the small intestine which pass them into the blood stream
structure & function of the lining of the small intenstine:
the lining of the small intestine is folded and there are microvilli present:
this increases the surface area
→ allows more membrane-bound disaccharidases to fit into the membrane
→ allows more absorption to take place
the digestion of starch by enzymes (arrows)
(lumen of the gut)
starch
→ amylase
maltose
→ maltase
glucose
(inside the epithelial cells of the small intestine)
the process of maltose being hydrolysed:
1) maltose molecules in the lumen of the gut diffuse towards membrane and bind to maltase
2) the membrane bound maltase hydrolyses maltose
3) two molecules of glucose are produced, which pass into the cytoplasm
which enzymes are involved in the digestion of protein?
-endopeptidase
-exopeptidase
-dipeptidase
where does protein digestion begin?
in the lumen of the stomach by protease enzymes
(PART 1) process of protein digestion in the stomach:
1) endopeptidase (a protease enzyme) hydrolyses peptide bonds within proteins, creating smaller sized protein chunks (dipeptides)
2) this enzyme is secreted along with hydrochloric acid, meaning the pH in the stomach is low (acidic)
3) the partially digested food moves from the stomach into the small intestine
(PART 2) process of protein digestion in the stomach:
1) fluid secreted by the pancreas travels to the small intestine and helps to neutralize the acidic mixture and increase the pH. this pancreatic juice contains endopeptidases and exopeptidase
2) lastly, there are dipeptidase enzymes found within the cell surface membrane of the epithelial cells in the small intestine
what do endopeptidases do?
they hydrolyse peptide bonds within polypeptide chains to produce dipeptides
what do exopeptidases do?
they hydrolyse peptide bonds at the ends of polypeptide chains to produce dipeptides
what does dipeptidase do?
it hydrolyses dipeptides into amino acids which are released into the cytoplasm of the cell
the digestion of protein by enzymes (arrows)
(lumen of the gut)
protein
→ (endopeptidase)
polypeptides
→ (exopeptidase)
dipeptides
→ (dipeptidase)
amino acids
(inside the cell-surface membrane of an epithelial cell)
the process of dipeptides being hydrolysed:
(lumen of the gut)
1) dipeptides diffuse towards membrane and bind to dipeptidase (enzyme-substrate complex)
2) dipeptides are hydrolysed into two amino acids which pass into the cytoplasm of the epithelial cell
does digestion of lipids happen immediately?
-there are several stages of breakdown that lipids go through prior to digestion
stages before digestion of lipase:
1) in the stomach, solid lipids are turned into a fatty liquid containing fat droplets
2) when the fatty liquid arrives in the small intestine, bile (which has been made in the liver and stored in the gallbladder) is secreted
3) the bile salts bind to the fatty liquid and break the fatty droplets into smaller ones via emulsification
what does bile contain?
bile salts
what is the purpose of emulsification?
helps to increase the surface area of the fatty droplets for action of digestive enzymes
digestion of lipids
-takes place solely in the lumen of the small intestine
-lipase enzymes break down lipids to glycerol and fatty acids
the digestion of lipids by enzymes (arrows)
lipids (large fat globule)
→ (bile salts)
emulsified lipids (small fat droplets)
→ (lipase)
fatty acids & glycerol
what is amylase’s substrate?
carbohydrates
where is amylase produced and released?
produced:
salivary glands & pancreas
released:
mouth & small intestines
what is maltases substrate?
disaccharides
where is maltese produced and released?
produced:
small intestine
released:
small intestine
what is the substrate of endopeptidases?
proteins
where are endopeptidases produced and released?
produced:
stomach & pancreas
released:
stomach & small intestines
where are exopeptidases produced and released?
produced:
pancreas
released:
small intestine
what is the substrate of dipeptidase?
dipeptidases
where are dipeptidases produced and released?
produced:
small intestine
released:
small intestine
what is the substrate of lipase?
lipids
where is lipase produced and released?
produced:
pancreas
released:
small intestine
what happens to the products of digestion?
they are absorbed through the intestinal lining
what is the mechanism of absorption for monosaccharides and amino acids?
co-transport
what is the mechanism of absorption for lipids?
a different method than co-transport
what is found within the cell-surface membrane of the epithelial cells in the ileum? (absorption of amino acids)
specific co-transport proteins
when can amino acids be co-transported?
when there are sodium ions present, for every sodium ion that is transported into the cell, an amino acid is transported in
(through a sodium dependent amino acid carrier protein)
which process is used for transport of amino acids?
facilitated diffusion, which requires the movement of molecules down their concentration gradient
where do amino acids travel?
amino acids diffuse across the epithelial cell and then pass into the capillaries via facilitated diffusion (through a channel protein)
what is the concentration gradient of sodium between?
from the lumen of the ileum into the epithelial cell
how is the concentration gradient of sodium maintained?
the active transport of sodium ions out of the cell and into the blood via a sodium-potassium pump at the other end of the cell
which method of transport is used to transport monosaccharides?
facilitated diffusion
where do monosaccharides travel?
across the epithelial cell and enter the capillary at the other end of the cell by facilitated diffusion
where are the sodium dependent glucose carrier proteins?
in the cell-surface membrane of the small intestine
how is the concentration gradient of sodium ions maintained?
by actively transporting sodium ions out of the epithelial cells into the blood
products of lipid digestion:
fatty acids, monoglycerides and glycerol
what do monoglycerides and fatty acids associate with? (absorption of lipids)
they associate with phospholipids and bile salts to form micelles (very small droplets)
why are micelles useful?
monoglycerides and fatty acids aren’t very soluble so the micelles aid the transport of these molecules to the surface of the epithelial cells
what happens after micelles associate?
-the micelles break down and add to a pool of fatty acids and monoglycerides that are dissolved in the small intestine solution surrounding the epithelial cells
-these freely dissolved molecules enter the epithelial cell by diffusion
-they are non-polar molecules so they can diffuse through the phospholipid bilayer of the cell membrane
complications with moving into blood (absorption of lipids)
-the short fatty acid chains within the epithelial cells can move directly into the blood via diffusion but the longer chains can’t
what do longer fatty acid chains do so they can move into the blood?
recombine with monoglycerides and glycerol to form triglycerides in the endoplasmic reticulum
what happens to the triglycerides? (steps)
1) they are packaged into lipoproteins called chylomicrons
2) these droplets are transported to a lacteal (a lymph vessel within the villus) via exocytosis
3) ventually, chylomicrons enter the bloodstream
what are chylomicrons?
-chylomicron structure is a spherical ‘case’ made of phospholipids and lipoproteins that hold the non-polar triglycerides inside, hidden from the aqueous environment of the cytoplasm and blood
cholesterol and phospholipids are also found within chylomicrons
which tissues are in the stomach and what do they do?
glandular tissue:
produces enzymes and stomach acid
muscular tissue:
churns food, mixing it with enzymes and acid
role of the acid in the stomach:
-the acid helps to unravel proteins to enable enzyme activity
-it lowers the ph which is optimal for stomach enzymes to work
-a lower pH is detrimental to many types of microorganisms which may be present in food
what are the three parts of the small intestine?
the duodenum, the jejunum and the ileum (end part)
what is the lumen of the small intestine?
the space through which food passes
which digestion occurs in the duodenum?
carbohydrate, protein and lipid digestion
what occurs in the jejunum and ileum?
soluble food molecules are absorbed into the bloodstream across the wall of the small intestine
ileum facts:
long and lined with finger-like villi:
increase the surface area over which absorption can take
what do the cells of all living organisms need?
a constant supply of reactants for metabolism
reactants: single celled vs multicellular
-single celled organisms can gain oxygen and glucose directly from their surroundings, and the molecules can diffuse to all parts of the cell quickly due to short diffusion distances
-larger organisms, however, are made up of many layers of cells, meaning that the time taken for substances such as glucose and oxygen to diffuse to every cell in the body would be far too long
how to solve the issues with reactants and large organisms:
(+ examples)
their exchange surfaces are connected to a mass transport system
(eg: the lungs are connected to the circulatory system)
what is mass transport?
the bulk movement of gases or liquids in one direction, usually via a system of vessels and tubes
advantages of mass transport systems:
-help to bring substances quickly from one exchange site to another
-help to maintain the diffusion gradients at exchange sites and between cells and their fluid surroundings
-ensure effective cell activity by keeping the immediate fluid environment of cells within a suitable metabolic range
what is the circulatory system?
the one-way flow of blood within the blood vessels carries essential nutrients and gases to all the cells of the body
what are haemoglobins?
a group of chemically similar molecules that are found in many different organisms
what is haemoglobin?
a globular protein & an oxygen-carrying pigment found in red blood cells
features of red blood cells:
-biconcave discs
-do not contain a nucleus
why are red blood cells biconcave?
high SA:V ratio for the diffusion of gases
why don’t red blood cells have a nucleus?
more space inside the cell for haemoglobin so that they can transport as much oxygen as possible
what structure does haemoglobin have?
quarternary; it is made up of four polypeptide chains
what subunits are haemoglobin made of?
globin protein subunits (two a-globins and two B-globins) and each subunit has a haem group
what are the four globin subunits held together by?
disulphide bonds
how are the four globin subunits arranged?
hydrophobic R groups are facing inwards → helps to preserve the 3D spherical shape
hydrophilic R groups are facing outwards
→ helps to maintain solubility
what ion is in haemoglobin and where?
the prosthetic haem group contains iron Il ion
what can this ion do?
reversibly combine with an oxygen molecule, forming oxyhaemoglobin
the presence of oxyhaemoglobin causes blood to appear…
bright red
each haemoglobin can carry…
four oxygen molecules
function of haemoglobin:
-binding oxygen in the lungs
-transporting the oxygen to the tissue to be used in respiration
-the existence of the iron II ion in the prosthetic haem group lets oxygen reversibly bind (none of the other amino acids in haemoglobin allow this)
why is haemoglobin better than oxygen travelling directly around the body?
oxygen is not very soluble in water and haemoglobin is, oxygen can be carried more efficiently around the body when bound to the haemoglobin
differences between types of haemoglobin:
the haem group is the same for all types of haemoglobin but the globin chains can differ substantially between haemoglobins from different species
other name for red blood cells:
erythrocytes
oxyhaemoglobin equation
402 + Hb = Hb40
oxygen + haemoglobin = oxyhaemoglobin
what is cooperative binding?
the binding of the first oxygen molecule results in a conformational change in the structure of the haemoglobin molecule, making it easier for each successive oxygen molecule to bind
terms for binding & unbinding of oxygen
associating, dissociating
loading, unloading
cm → dm
divide by 10
what does an oxygen dissociation curve show?
the rate at which oxygen associates and dissociates, with haemoglobin at different partial pressures of oxygen
what is partial pressure (of oxygen)?
the pressure exerted by oxygen within a mixture of gases
when is haemoglobin saturated?
when all of its oxygen binding sites are taken up with oxygen; so when it contains four oxygen molecules
what is haemoglobin’s affinity for oxygen?
the ease with which haemoglobin binds and dissociates with oxygen
high affinity
it binds easily and dissociates slowly
low affinity
it binds slowly and dissociates easily
haemoglobin’s affinity for oxygen changes at…
different partial pressures of oxygen
shape of dissociation curve at low partial pressures of oxygen: (association)
shallow curve:
due to the shape of the haemoglobin molecule it is difficult for the first oxygen molecule to bind to haemoglobin; this means that binding of the first oxygen occurs slowly
(haemoglobin has a low affinity for oxygen at low pO^2)
shape of dissociation curve at middle level partial pressures of oxygen: (association)
steeper curve:
after the first oxygen molecule binds to haemoglobin, the haemoglobin protein changes shape (cooperative binding), making it easier for the next haemoglobin molecules to bind
this speeds up binding of the remaining oxygen molecules
shape of dissociation curve at high partial pressures of oxygens: (association)
levelling off:
as the haemoglobin molecule approaches saturation it takes longer for the fourth oxygen molecule to bind due to the shortage of remaining binding sites
(high affinity for oxygen at high p02)
explanation of the shape of dissociation curve at high partial pressures of oxygen: (disassociation)
R → L
in the lungs, where p02 is high, there is very little dissociation of oxygen from haemoglobin
shape of dissociation curve at medium partial pressures of oxygen: (disassociation)
R → L
steep region:
-oxygen dissociates readily from haemoglobin
-this region corresponds with the partial pressures of oxygen present in the respiring tissues of the body
-ready release of oxygen is important for cellular respiration
(low affinity)
shape of dissociation curve at low partial pressures of oxygen: (disassociation)
dissociation slows again; there are few oxygen molecules left on the binding sites, and the release of the final oxygen molecule becomes more difficult
what is the bohr shift?
a shift to the right in the oxygen dissociation curve due to carbon dioxide level changes
what happens to haemoglobin when the partial pressure of carbon dioxide in the blood is high?
haemoglobin’s affinity for oxygen is reduced
where does the bohr shift occur?
in respiring tissues, where cells are producing carbon dioxide as a waste product of respiration
why does haemoglobin’s affinity for oxygen reduce when the partial pressure of carbon dioxide in the blood is high?
-CO2 lowers the pH of the blood
-CO2 combines with water to form carbonic acid
-carbonic acid dissociates into hydrogen carbonate ions and hydrogen ions
-hydrogen ions bind to haemoglobin, causing the release of oxygen
carbonic acid (formula)
CO2 + H2O
why is the bohr shift helpful in respiring tissues?
it means that haemoglobin gives up its oxygen more readily in the respiring tissues where it is needed
where does the dissociation curve shift when CO2 levels increase & what does this mean?
to the right:
enhances the unloading of oxygen into tissues to meet the oxygen demand of the tissue.
what is cardiac output?
the volume of blood that is pumped by the heart (the left and right ventricle) per unit of time
cardiac output of an average adult:
4.7 litres of blood per minute when at rest
cardiac output of fitter individuals:
often have higher cardiac outputs due to having thicker and stronger ventricular muscles in their hearts
when does cardiac output increase & why?
when an individual is exercising:
so that the blood supply can match the increased metabolic demands of the cells
what is heart rate?
the number of times a heart beats per minute
what is stroke volume?
the volume of blood pumped out of the left ventricle during one cardiac cycle
cardiac output equation:
heart rate x stroke volume
what do the variating globin polypeptides tell us about haemoglobin?
the precise properties of haemoglobin
what do haemoglobin types vary in?
their oxygen-binding properties
factors that can impact the evolution of haemoglobin within a species:
-environmental factors
oxygen at high altitudes:
the partial pressure of oxygen in the air is lower at higher altitudes
how have different animals adapted to low levels of oxygen at high altitudes?
(which animals)
llamas:
they have haemoglobin that binds much more readily to oxygen (higher affinity)
↳ this lets them get a sufficient level of oxygen saturation in their blood when the partial pressure of oxygen (pO2) in the air is low
where has the disassociation curve shifted for animals at high altitudes?
to the left
what is foetal haemoglobin?
the haemoglobin of a developing foetus
adaptations of foetal haemoglobin:
a higher affinity for oxygen than adult haemoglobin
why is it important for foetal haemoglobin to have a high affinity?
it allows a foetus to obtain oxygen from its mother’s blood at the placenta:
-fetal haemoglobin can bind to oxygen at low pO2
-at this low pO2 the mother’s haemoglobin is dissociating with oxygen
where has the disassociation curve shifted when looking at foetal haemoglobin?
shifts to the left of that for adult haemoglobin
what does this shift mean?
at any given partial pressure of oxygen, foetal haemoglobin has a higher percentage saturation than adult haemoglobin
what happens to a babies’ haemoglobin at birth & why?
-after birth, a baby begins to produce adult haemoglobin which gradually replaces foetal haemoglobin
-this is important for the easy release of oxygen in the respiring tissues of a more metabolically active individual
