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CHAPTER 1 THE CELL & BIOMOLECULES OF LIFE (Part 1)

(A) Outline the cell theory with the understanding that cells are the smallest unit of life,
all cells come from pre-existing cells, and living organisms are composed of cells

A little History
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1665 – Englishman Robert Hooke examines cork under a compound microscope
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1675 – Dutchman Antonie van Leeuwenhoek discovers unicellular organisms
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K
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the father of modern pathology)
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All living organisms are composed of one or more cells
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The cell is the most basic unit of structure and function in living organisms
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Cells arise from pre-existing cells by cell division
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 A buffer solution to maintain pH
 A low temperature of 4°C to inhibit protease activity and preserve the unique 3D
conformation of proteins in organelles
Methods of mechanical rupturing of cell membrane
 Ultrasound
 Osmotic Lysis (rupture protoplasts)
 Pressure
 Homogeniser (abrasive equipment)

Differential Centrifugation
 Used to separate organelles and cellular components as a function of their sedimentation coefficient,
dependent on size and density (as well as viscosity of the medium)
 Allows for the study of isolated organelles to study cell structure and function
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 A series of pellets containing cell organelles of decreasing sizes can therefore be obtained
 Nuclei, Mitochondria/Chloroplasts/Peroxisomes & Lysosomes, Plasma Membrane/Microsomes
(fragmented ER)/Polyribosomes, Ribosome Subunits, Cytosol

Autoradiography
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Used to identify the synthesis and cellular distribution sites of metabolic products by tagging specimen
molecules with radioisotopes such as 15N and 32P
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Steps (extra info)
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Tissue specimens exposed to radioactive label
Tissues washed off to remove excess label and later fixed and sectioned
Sections are placed on microscopic slides
Slides dipped in melted photographic emulsion in the darkroom
Slides are dried and stored in the dark
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Grains exposed in the emulsion mark sites of inactivity

Organelles
Membranous organelles
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Rough Endoplasmic Reticulum
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Smooth Endoplasmic Reticulum
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Golgi Apparatus
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Lysosomes
 Vesicles
 Vacuoles
 Mitochondria (double membrane)
 Chloroplasts (double membrane)
 Nucleus (double membrane)
Non-membranous organelles
 Centrioles
 Ribosomes
 Flagella
 Cilia
Other parts
 Cell Wall
 Cytosol (cytoplasmic fluid)
 Cytoplasm
 Nucleus
 Nucleolus
 Cell Plasma Membrane

(C) Outline the functions of the membrane systems and organelles listed in (B)
MEMBRANOUS ORGANELLES
a) Nucleus (double membrane)
Description
 Largest membranous organelle; spherical or oval in shape with a size of between 5-20 µm
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 Cells may be uninucleated, binucleated or multinucleated
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(DNA replication and mRNA transcription occurs here)

Contains
i) Nuclear envelope
 Double phospholipid membrane which separates the contents of the nucleus from the
cytoplasm
 Each of the two membranes is a lipid bilayer (So the double membrane is basically two bilayers
with a gap in between them)
 Inner and outer membranes are continuous with each other; region between them known as
perinuclear space, which is contiguous with the endoplasmic reticulum lumen; Outer
membrane contiguous with the membrane of the endoplasmic reticulum
 Perforated by nuclear pores, made up of a large protein complex which allows
macromolecules such as mRNA, tRNA and rRNA to exit the nucleus, and proteins to enter
and exit the nucleus
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Appears as light-coloured patches
 Tightly coiled chromatin known as heterochromatin (not being transcribed)
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• The pars fibrosa contains large loops of DNA from a number of chromosomes containing
genes from which rRNA is transcribed to become part of ribosomes
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Function: Composed of DNA carrying rRNA genes to synthesize ribosomal RNA, which is
involved in the assembly of ribosomes required for translation (protein synthesis)
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It forms a separate compartment allowing metabolic reactions to be localized
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protein hormones
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Storage and release of Ca2+ especially in the Sarcoplasmic Reticulum of muscles
Package certain proteins from rough ER in the cisternae for transport
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 At the trans face (concave face), the Golgi Apparatus breaks up to form vesicles called lysosomes
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e) Lysosomes
Description
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Spherical sacs of 0
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2 µm in diameter
It is bound by a single membrane
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It serves as a storage vesicle to keep the enzymes apart from the rest of the cell, hence
preventing it from destroying the cell
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2 types of lysosomes: Primary lysosome and Secondary lysosome
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These enzymes were first synthesized on the rER and later transported to Golgi Apparatus
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• Autolysis
• Cells (injured and dying tissues) can self-destruct through the mass release of
lysosomal contents into the whole cell
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f) Vacuoles
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In animal cells, small, mobile vacuoles
In plant cells, large (central) permanent vacuole
 Solution within the tonoplast (vacuolar membrane) known as cell sap
 Functions
 Storage of organic compounds
 Disposal site for toxic metabolic by-products
 Containment of pigments
 Cell growth & elongation (water accumulation causes cytoplasmic contents to be
pushed to the periphery)

g) Mitochondria (double membrane)
Description
 Spherical, rod shaped, double membraned organelle
 Outer membrane is smooth, inner membrane is highly convoluted with cristae to increase
surface area for various enzyme systems and proteins embedded in the inner membrane;
allows for the localisation of more ATP synthase and electron transport chains
 Selectively permeable inner membrane that allows for the formation of an electrochemical gradient
 Narrow, fluid-filled space between two membranes known as inter-membrane space
 Compartment enclosed by inner membrane is the mitochondrial matrix which houses
DNA, RNA and ribosomes
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The light-dependent reactions of photosynthesis occur at the thylakoid membrane while the lightindependent reactions (Calvin cycle) occur in the stroma
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– 1 molecule of rRNA (16S) + 20 proteins

– 3 molecules of rRNA + 47 proteins
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b) Centrioles
Description
• Pair of hollow cylinders located near nucleus; 0
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3 to 0
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Function
• Organize spindle fibres during cell division
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Label the various organelles and parts of the animal cell below

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