3B - more exchange and transport systems Flashcards
why can’t large biological molecules be absorbed from the gut into the blood?
because they’re too big to cross the membrane.
what happens to large molecules during digestion?
they’re broken down into smaller molecules (e.g. glucose and amino acids) which can move across the cell membranes.
which reaction breaks down the large molecules?
hydrolysis reaction.
what are carbohydrates broken down into?
disaccharides.
what are fats broken down into?
fatty acids and monoglycerides.
what are proteins broken down into?
amino acids.
what are enzymes used for?
to break down biological molecules in food.
what enzyme catalyses the breakdown of starch?
amylase.
what is starch a mixture of?
two polysaccharides.
how does amylase work?
by catalysing a hydrolysis reaction that breaks the glycosidic bonds in starch to produce maltose (a disaccharide).
where is amylase produced?
salivary glands (releases amylase in the mouth) and the pancreas (releases amylase in the small intestine).
what are membrane-bound disaccharidases?
enzymes that are attached to the cell membranes of epithelial cells lining the ileum.
what is the ileum?
the final part of the small intestine.
what do membrane-bound disaccharidases break down?
disaccharides (into monosaccharides).
name three disaccharides.
maltose, lactose and sucrose.
how can monosaccharides be transported across the epithelial cell membranes in the ileum?
via transporter proteins.
which enzyme catalyses the breakdown of lipids?
lipase enzymes.
what do lipids break down into?
fatty acids and monoglycerides.
which bonds are broken in lipids?
ester bonds.
where are lipases made?
mainly in the pancreas (secretes into the small intestine).
what are bile salts produced by?
the liver.
what do bile salts do?
they emulsify lipids.
what does it mean when lipids are emulsified?
they form small droplets.
why is it better that lipids break down into small droplets?
several small lipid droplets means that the surface area is larger which means there’s more surface area of lipid for lipases to work on.
what happens to the fatty acids and monoglycerides?
they stick with the bile salts to form tiny structures called micelles.
what do micelles do?
they help the products of lipid digestion to be absorbed.
what enzymes break down proteins?
peptidases.
what do proteins break down into?
amino acids.
which bonds join amino acids together?
peptide bonds.
what are the three types of peptidases?
endopeptidases, exopeptidases and dipepridases.
what do endopeptidases do?
they act to hydrolyse peptide bonds within a protein.
what do exopeptidases do?
they act to hydrolyse peptide bonds at the ends of protein molecules. they remove single amino acids from proteins.
give three examples of endopeptidases.
pepsin, trypsin and chymotrypsin.
what are dipeptidases?
they’re exopeptidases that work specifically on dipeptides.
what do dipeptisases do?
they separate the two amino acids that make up a dipeptide by hydrolysing the peptide bond between them
where are dipeptidases often located?
in the cell-surface membrane of epithelial cells in the small intestines.
where are the products of digestion absorbed?
across the ileum epithelium into the bloodstream.
how is glucose absorbed?
by active transport via a co-transporter protein.
how is galactose absorbed?
active transport via a co-transporter protein.
how is fructose absorbed?
via facilitated diffusion through a different transporter protein to glucose and galactose.
where do micelles help to move fatty acids and monoglycerides to?
the epithelium.
why can micelles ‘release’ the monoglycerides and fatty acids?
because they constantly break up and reform.
are whole micelles taken up across the epithelium?
no.
why can monoglycerides and fatty acids diffuse directly across the epithelial cell membrane?
because they’re lipid-solvable.
how are amino acids absorbed?
sodium ions are actively transported out of the epithelial cells into the ileum. they then diffuse back into the cells through sodium-dependent transporter proteins in the epithelial cell membranes, carrying the amino acids with them.
where is haemoglobin found?
in the red blood cells.
what is the role of haemoblobin?
to carry oxygen around the body.
what is haemoglobin?
a large protein with a quaternary structure.
what is haemoglobin quaternary structure made up of?
four polypeptide chains, each chain having a haem group which contains an iron ion (gives haemoglobin its red colour).
how many molecules of oxygen can each molecule of human haemoglobin carry?
4.
where does oxygen join to haemoglobin?
in the lungs.
what is formed when oxygen joins to haemoglobin?
oxyhaemoglobin.
where does oxyhaemoglobin turn back to haemoglobin?
near body cells that need oxygen.
what is it called when an oxygen molecule joins to haemoglobin?
association or loading.
what is it called when oxygen leaves oxyhaemoglobin?
dissociation or unloading.
what is affinity for oxygen?
the tendency a molecule has to bond with oxygen.
what does haemoglobin a affinity for oxygen depend on?
the conditions it’s in.
what’s a condition that affects the affinity for oxygen?
partial pressure of oxygen (pO2)
what is partial pressure of oxygen?
the measure of oxygen concentration.
does oxygen load onto haemoglobin to form oxyhaemoglobin where there’s a high or low pO2?
high.
where does oxygen enter blood capillaries?
at the alveoli in the lungs.
do alveoli have a high or low pO2?
high.
when happens in cells to reduce the pO2?
respiration.
where do red blood cells deliver oxyhaemoglobin to?
respiring tissues.
what are some factors of the alveoli in the lungs?
- HIGH oxygen concentration
- HIGH pO2
- HIGH affinity
- oxygen LOADS
what are some factors of respiring tissues?
- LOW oxygen concentration
- LOW pO2
- LOW affinity
- oxygen UNLOADS
what does an oxygen dissociation curve show?
how saturated the haemoglobin is with oxygen and any given partial pressure.
