Biology Unit 1.2 Revision Notes (Digestive System)

I hope you find these useful!

Basically, I have divided my notes up into parts of the syllabus, so 1.1, 1.3, 1.4, 1.5 and 1.6 are separate documents, but are all on here.

The part of the syllabus relevant to these notes is on the cover page at the start of the notes.

Sorry for any spelling mistakes or anything :L.

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The The gross structure of the human digestive system limited to oesophagus, stomach, small and
large intestines, and rectum. The glands associated with this system limited to the salivary
Digestive glands and the pancreas.
Digestion is the process in which large molecules are hydrolysed by enzymes to produce smaller…

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Condensation and the formation of peptide bonds linking together amino acids to form
polypeptides. The relationship between primary, secondary, tertiary and quaternary structure,
and protein function.

The biuret test for proteins.

Proteins and Amino Acids

Monomers of proteins are amino
A dipeptide is formed when two
amino acids join…

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acids in polypeptide

The way in which a
polypeptide chain is
Secondary folded into a helix or
pleated structure

The irregular folding
of secondary
Tertiary structure into a
globular shape

Sometimes proteins
are made of several
Quaternary polypeptide chains
wound together

Structural Levels

A protein's shape determines its function.…

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Protein Functions

Biuret Test


Denature ­ loss of specific 3D shape due to the breaking of hydrogen bonds holding the
structure together; the protein loses its specific shape and will no longer function

All proteins including enzymes will denature under certain conditions
Conditions that cause proteins to denature:

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Enzyme Enzymes as catalysts lowering activation energy through the formation of enzyme-substrate
The lock and key and induced fit models of enzyme action.

Enzyme ­ a biological catalyst which speeds up the rate of chemical reactions by lowering
the activation energy

They catalyse metabolic reactions in your body…

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Enzyme The properties of enzymes relating to their tertiary structure. Description and explanation of the
effects of temperature, competitive and non-competitive inhibitors, pH and substrate
Properties concentration.

Candidates should be able to use the lock and key model to explain the properties of enzymes.
They should also recognise its limitations…

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Most human enzymes work best at pH 7, but there are some exceptions (like pepsin, which
works best at pH 2 and is found in the stomach)
Above and below the optimum pH, the H+ and OH- ions can mess up ionic and hydrogen
bonds, thus causing the active site…

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Competitive Inhibitors

Are molecules that are similar in shape to the substrate
They can enter the active site and stop the substrate entering and being catalysed until
the inhibitor leaves
V-Max can be achieved if substrate concentration is very high since the inhibitor is
unlikely to reach the active site…

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Carbohydrat Within this unit, carbohydrates should be studied in the context of the following
e Digestion
Starch, the role of salivary and pancreatic amylases and of maltase located in the
intestinal epithelium
Disaccharides, sucrase and lactase.

Biological molecules such as carbohydrates and proteins are often polymers and are based on…




These notes are very well presented and provide useful information in the form of text , diagrams and flow diagrams on the digestive system, protein, enzymes and carbohydrates, Use them as your notes, build on them from the resources you use yourself and then use them to create revision cards.  They would provide a useful basis for any student studying these topics at GCE level.

Sasha Dean


Thank You -  these notes are amazing!!

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