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B io Factsheet
September 1997 Number 4
Structure to function in eukaryotic cells
The cell surface membrane and the membranes which form organelles in enzymes and substrates to be concentrated and pH to be optimised.
eukaryotic cells all have the same basic structure, known as the fluid Membranes can therefore be said to compartmentalise the interior of
mosaic model. Such membranes provide control of the entry and exit of eukaryotic cells.
substances into cells and organelles and such control is a result of the
phospholipid bilayer and membrane proteins. The relationship between structure and function can be described in terms
of the whole cell or in terms of the individual organelles of the eukaryotic
In eukaryotic cells, such membranes divide the cytoplasm into multiple cell.
compartments (organelles). Organelles allow different functions to occur
efficiently and simultaneously in different parts of the cell. For example, Table 1 describes the structure and function of a motor neuron cell which is
the outer double membrane of the mitochondrion separates out those commonly featured in examination questions. The structure and function
reactions which occur in mitochondria from those in the general cytoplasm. of eukaryotic organelles is described overleaf.
Furthermore, the internal membranes of the mitochondria allow the enzymic
reactions of the Kreb's cycle to be kept quite separate from the electron Exam Hint - Structure to function questions are very commonly set
transfer chain reactions (ETC). This is essential since both sets of reactions on all A level Biology syllabuses. They are one of the syllabus areas
have different enzymes, hence different pH optima. By splitting up the where all candidates should be capable of gaining the highest marks.
cytoplasm of the mitochondria, the membranes which form the crista allow Once the functions of organelles have been memorised, candidates
should become confident at interpreting the function of unknown cells.
Table 1.
Cell Structure Function
Motor Neuron Cell body contains: Provides the genetic code for the production of
nucleus neurotransmitter substances, e.g. acetylcholine and
(i) Nucleus enzymes, eg. cholinesterase.
(ii) dense groups of ribosomes For production and transport of proteins and
Nissl and endoplasmic reticulum neurotransmitters.
granules called Nissl granules
Long axons For rapid transmission of nerve impulse. Synapses, where
dendrites two nerves join, is the slowest part of transmission, so
the longer the axon, the fewer the synapses and the faster
the impulses transmitted.
axon Axon contains axoplasm Allows transport between cell body and axon
Nodes of Ranvier between Allows Na+ /K+ pump to operate which sets up resting
Schwann cells potential. Schwann cells of myelin sheath speed up the
axon may be a metre or more in length
impulse because they increase the surface area for
transmission of current.
High phospholipid content in Provides electrical insulation.
membrane of Schwann cell
nodes of
Synaptic knob at end of
dendrite contains:
(i) many mitochondria To provide ATP for active refilling of synaptic vesicles.
of nerve
impulse (ii) numerous vesicles For modification and release of chemical transmitters
across the synapse.
Many dendrites To allow communication with other neurons.

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Structure to function in eukaryotic cells Bio Factsheet
Structure and Function of Organelles Structure Function
Nucleus Double nuclear envelope To enclose and protect DNA (normally visible as
chromatin granules).
Nuclear pores. Allow entry of substances such as nucleotides for DNA
replication and exit of molecules such as mRNA during
protein synthesis.
Normally, the nuclear pores are Small molecules pass through the pores by diffusion,
plugged by an RNA/protein whereas large molecules such as partly completed
complex. ribosomes pass through actively.…read more

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Structure to function in eukaryotic cells Bio Factsheet
Cell Structure Function
Endoplasmic Reticulum Endoplasmic reticulum is a Allows transport of substances within the cell.
system of hollow tubes and
Rough endoplasmic reticulum The ribosomes on the rough endoplasmic reticulum may
(rer) is covered with ribosomes synthesise proteins which can then be transported through
and consists of an the cell in the cavities of the endoplasmic reticulum.…read more

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Structure to function in eukaryotic cells Bio Factsheet
Cell Structure Function
Lysosomes Lysosomes are vesicles which When released, these enzymes can break down old
contain hydrolytic enzyme, organelles, storage molecules or, indeed, the whole cell,
collectively known as when it dies.
Chloroplasts. Double Membrane Allows the isolation of photosynthetic reactions.…read more

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Structure to function in eukaryotic cells Bio Factsheet
Practice Questions Answers
1. Outline the similarities between chloroplasts and mitochondria. Marking points are shown by semicolons
2. The diagram shows a generalised eukaryotic cell. 1. Both organelles are surrounded by two membranes;
Both show internal compartmentalisation - i.e.…read more


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