Digestive system Flashcards
Describe physical digestion
Food is broken down into smaller pieces by the teeth in the mouth. It is then sent to the stomach where it is broken down further by the churning movement of the stomach muscles.
Explain why food is broken down
Food is broken down so that the surface area of the food is increased which increases the rate of digestion.
Describe chemical digestion
The polymers in our food are insoluble. They can’t be directly absorbed into our blood stream and assimilated into new products. Instead they are hydrolysed by enzymes in the mouth, stomach and small intestine. They are broken down into smaller, more soluble molecules.
What is the name of the muscle contractions in the oesophagus and stomach?
Peristalsis
Explain how the stomach digests food?
Food enters the stomach from the oesophagus and is controlled by sphincter muscles which control entry and exit. The folds in the stomach lining allow it to expand to hold up to 4 litres of food and water in humans. The stomach wall secretes digestive juices which contain hydrochloric acid, pepsin ( a digestive enzyme ) and mucus. the pepsin hydrolyses large protein molecules into smaller chain polymers. It only works at a specific pH and the food is converted to chyme.
Name the two main parts of the small intestine
The duodenum and the ileum
Explain what happens to food in the small intestine
The acidity of the chyme is neutralised by bile and pancreatic juices which also breaks it down into smaller molecules. In the ileum the small soluble molecules ( glucose, amino acids etc ) are absorbed through villi that line the small intestine. These molecules diffuse through the small intestine via facilitated diffusion and active transport.
Explain what a monomer is and give an example
A monomer is a single molecule which can bond to other molecules. An example would be an amino acid
Explain what a polypeptide is
A polypeptide is a group of amino acids joined by peptide bonds ( two joined together is called a dipeptide )
What is the same general structure of an amino acid and state how they vary.
A carbon atom bonded to an amino group ( NH2 hence amino acid ) a carboxyl group (COOH) and a hydrogen. What makes them different is the variable group often labelled R.
How are polypeptides formed?
Amino acids are joined by a condensation reaction in which an H2O molecule is formed from an OH on one amino acid and a H from another. The OH comes from the carboxyl group and the H comes from the amino group. This creates a peptide bond.
What are the four “levels” of protein structure?
Primary
Secondary
Tertiary
Quarternary
Describe a primary structure protein
The sequence of amino acids in a polypeptide chain.
Describe a secondary structure protein
The polypeptide chain doesn’t remain straight due to hydrogen bonds forming between the amino acids which cause it to kink into one of two shapes-alpha helix or beta pleated sheets.
Describe a tertiary structure protein
The secondary structure protein is often further coiled which causes more bonds to form between more parts of the polypeptide chain. A single polypeptide chain will only reach a tertiary structure. The bonds formed include ionic bonds, disulphide bonds etc
