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Organelles is taught in the note for Cell Biology. Read it below and look for the section on this topic.

Cell Biology

14 min read

Cell theory

The cell theory says that all living things are made of one or more cells, the cell is the basic unit of structure and function, and new cells arise only from existing cells. It was built from the work of Hooke, who named cells, Schleiden and Schwann, who showed that plants and animals are made of cells, and Virchow, who showed that cells come from cells.

Organelles

The cell contains small structures called organelles, each with a job. An electron microscope shows their detail.

An animal cellA rounded animal cell with its parts labelled: cell membrane around the outside, cytoplasm filling the cell, a large nucleus with a darker nucleolus, mitochondria, ribosomes, endoplasmic reticulum and a Golgi body.cell membranenucleusnucleolusmitochondrionribosomesGolgi bodyendoplasmic reticulumcytoplasm
A plant cellA plant cell with a thick cell wall outside the cell membrane, a large central vacuole, green chloroplasts, a nucleus, and mitochondria. These parts differ from an animal cell, which has no cell wall, no large vacuole and no chloroplasts.cell wallchloroplastnucleuslarge vacuolecell membranemitochondrion
OrganelleStructureFunction
NucleusDouble membrane with pores, contains chromatinControls the cell; holds DNA
MitochondrionDouble membrane, inner folds called cristaeAerobic respiration: makes ATP
RibosomeSmall particles, free or on rough ERProtein synthesis
Rough ERMembranes with ribosomesMakes and transports proteins
Smooth ERMembranes without ribosomesMakes lipids
Golgi apparatusStack of flat sacsModifies and packages proteins
LysosomeSac of enzymesDigests worn-out parts and bacteria
ChloroplastDouble membrane, grana and stromaPhotosynthesis
VacuoleSac of cell sapStores water and supports the cell

Biological molecules

Cells are built from four main groups of organic molecules.

Building blocks of biological moleculesThree simple pictures. Many glucose units join to make starch. Amino acids, each with an amino group and a carboxyl group, join in a chain to make a protein. A fat molecule is made of one glycerol joined to three fatty acids. Carbohydrates, proteins and fats are the main biological molecules.glucoseCarbohydrate: glucose units → starchamino acid chainProtein: amino acids joinedFat: glycerol + 3 fatty acidsEnzymes are proteins that speed up reactions.
MoleculeMade ofRoleTest
CarbohydratesSugars (C, H, O)Energy and structureBenedict’s (reducing sugar), iodine (starch)
ProteinsAmino acidsEnzymes, structure, hormonesBiuret test (purple)
LipidsGlycerol and fatty acidsEnergy store, membranesEmulsion test (cloudy)
Nucleic acidsNucleotidesStore the genetic code

Enzymes

Enzymes are protein catalysts that speed up the reactions of the cell. Each has an active site that fits only one substrate. High temperatures change the shape of the active site (denaturation), so the enzyme stops working. Each enzyme works best at an optimum pH and temperature.

The lock and key model of an enzymeAn enzyme has a special-shaped region called the active site. Only a substrate with a matching shape fits, like a key in a lock. The substrate binds to form an enzyme–substrate complex, the reaction takes place, and the products leave the enzyme unchanged, ready to be used again. High temperature or the wrong pH changes the shape of the active site, so the enzyme is denatured.enzymesubstrateenzyme–substrate complexproducts leaveenzyme unchanged
The rate rises to an optimum near 37 °C and then falls sharply as the enzyme is denatured.
Try itEnzyme rate and temperature

Choose a temperature to see the relative rate of reaction of an enzyme with an optimum of 37 °C.

Check yourself Which organelle makes ATP in aerobic respiration?
Check yourself Which test shows protein?
Check yourself Why does a very high temperature stop an enzyme?

Key terms

Cell theory
All organisms are made of cells, and cells come from cells.
Organelle
A structure in a cell with a special job.
Enzyme
A protein that speeds up a reaction.
Substrate
The substance an enzyme acts on.

Summary

  • Cell theory: all living things are made of cells, which arise from cells.
  • Organelles each carry out a function.
  • Carbohydrates, proteins, lipids and nucleic acids are the main biological molecules.
  • Enzymes are proteins with an active site; temperature and pH affect them.
Cell theory Biological molecules