These are comprehensive, organised, and easy-to-read notes that cover a three-unit module consisting of thirteen lectures on cell structure and function, cell communication, as well as cell death. These are perfect for bioscience and animal/veterinary students as well as prospective students who ne...
Basic Cell Structure
Describe the basic structures of proteins, nucleic acids, carbohydrates and phospholipids.
Outline the differences between eukaryotic and prokaryotic cells.
Outline the functions of the plasma membrane; cytoskeleton; nucleus; endoplasmic
reticulum; Golgi apparatus; secretory vesicles; endosomes; lysosomes and mitochondria.
Identify the above cellular structures as seen using appropriate imaging techniques.
POLYMER Protein
MONOMER Amino acid
Proteins (polypeptides) contain hundreds of
amino acids in long chains. These chains fold
in onto themselves to create complex 3D
PROPERTIES shapes, which are specific to their functions.
Proteins exist in solution, in chains and in
complexes associated with one another and
connect to, or pass through, the membranes.
Every amino acid has a central carbon atom to
which are attached four different chemical
groups:
- Amino group (–NH2)
- Carboxyl group (– COOH)
STRUCTURE - The hydrogen atom (– H)
- R (side) group
Proteins can have a structure which is either
primary, secondary, tertiary or quaternary,
depending on the specific bonding and folding
within or between different amino acid chains.
Enzymes – increasing the rate of reaction
Protection – e.g. immunoglobulin (antibody)
FUNCTION Receptors – e.g. rhodopsin
Transport – e.g. haemoglobin
Hormonal – e.g. insulin
DNA RNA Protein
Transcription Translation
In the nucleus In the cytoplasm
, 2
POLYMER Nucleic acids
MONOMER Nucleotide
Nucleotides are monomers of DNA and RNA.
ATP is also a nucleotide. Nucleic acids are
PROPERTIES classed as acids due to the negatively charged
phosphate groups. Hydrogen bonds form
between the bases (A & T or U, C & G)
Individual nucleotides are made up of three
components:
STRUCTURE
- A pentose sugar
- A phosphate group
- A nitrogen-containing organic base
Information storage (DNA/RNA) – provide
the code to describe how proteins are made.
In eukaryotes, DNA is found in the nucleus;
RNA is found in the cytoplasm.
FUNCTION
Energy transfer (ATP) – energy is released
when the highly energetic bond between the
phosphate groups is broken.
POLYMER Carbohydrates
MONOMER Monosaccharide
Monosaccharides are sweet-tasting, soluble
substances.
Examples of monosaccharides include
PROPERTIES glucose, galactose and fructose.
Glycogen is an insoluble, compact and highly
branched carbohydrate used by animals to
store energy in a form of glucose monomers.
Glucose is a hexose (6-carbon) sugar. The
atoms of carbon, hydrogen and oxygen can be
STRUCTURE
arranged in many different ways, giving rise to
different isomers.
Energy source – glycogen can be rapidly
broken down to form glucose monomers,
which are used in respiration.
FUNCTION Energy storage – glycogen, which is a
carbohydrate, is found in animals and
bacteria. In animals, it is stored as small
granules mainly in the muscles and the liver.
, 3
POLYMER Lipids
MONOMER Glycerol/fatty acids
Contain carbon, hydrogen and oxygen
Insoluble in water
PROPERTIES Soluble in organic solvents such as alcohols
and acetone.
The main groups of lipids are triglycerides (fats
and oils) and phospholipids.
Phospholipids are a major component of the
STRUCTURE
membrane. They contain a hydrophobic tail and a
hydrophilic head. The hydrophilic parts of the
phospholipids orient themselves to face the
water molecules.
Energy source – when oxidised, lipids provide
more than twice the energy as the same mass of
carbohydrate.
Waterproofing – lipids are insoluble in water and
therefore useful as a waterproofing. Mammals
produce an oily secretion from the sebaceous
glands in the skin.
Insulation – fats are slow conductors of heat and
FUNCTION
when stored beneath the body surface help to
retain body heat. They also act as electrical
insulators in the myelin sheaths around nerve
cells.
Protection – fat is often stored around delicate
organs, such as the kidney.
Structural – cholesterol is used to strengthen the
cell membrane by making it more rigid.
All of these molecules are interrelated:
DNA replication is catalysed by proteins
RNA regulated and catalyses protein formation
DNA translation to RNA is catalysed by proteins
Proteins catalyse phospholipid formation
Phospholipids control the locations of DNA, RNA and
proteins
, 4
Comparison of prokaryotic and eukaryotic cells
PROKARYOTIC CELLS EUKARYOTIC CELLS
No true nucleus, only an area where DNA is
Distinct nucleus, with a nuclear envelope
found
(Pro) DNA is not associated with proteins DNA is associated with proteins called histones
Some DNA may be in the form of circular
There are no plasmids and DNA is linear
strands called plasmids
Membrane-bound organelles, such as
No membrane-bound organelles
mitochondria, are present
Ribosomes are smaller (70S) Ribosomes are larger (80S)
Cell wall made of murein (peptidoglycan) No cell wall, just cell membrane
May have an outer mucilaginous layer called a
No capsule
capsule
Roles of structures found in a bacterial cell
CELL STRUCTURE ROLE
The physical barrier that excludes certain substances and
Cell wall protects against mechanical damage and osmotic lysis
Protects bacterium from other cells and helps groups of
Capsule bacteria to stick together for further protection
Acts as a differentially permeable layer, which controls
Cell-surface membrane the entry and exit of chemicals
Possesses the genetic information for the replication of
Circular DNA bacterial cells
Possesses genes that may aid the survival of bacteria in
Plasmid adverse conditions, e.g. produces enzymes that break
down antibiotics
, 5
Roles of structures found in a eukaryotic cell
CELL STRUCTURE ROLE
Acts as the control centre of the cell through the production of mRNA and tRNA and
hence protein synthesis
Nucleus Retains the genetic material of the cell in the form of DNA and chromosomes
Manufactures ribosomal RNA and ribosomes
The site of the aerobic stages of respiration (the Krebs cycle and the oxidative
phosphorylation pathway)
Mitochondrion
Responsible for the production of ATP
Rough endoplasmic reticulum (RER)
Provides a large surface area for the synthesis of proteins and glycoproteins
Endoplasmic Provides a pathway for the transport of materials, especially proteins, throughout the
cell
reticulum
Smooth endoplasmic reticulum (SER)
Synthesises, stores and transports lipids and carbohydrates
Adds carbohydrates to proteins to form glycoproteins
Release enzymes to the outside of the cell (exocytosis) in order to destroy material
around the cell
Lysosomes
Digests wore out organelles so that useful chemicals they are made of can be re-used
Completely break down cells after they have died (autolysis)
Conversion of the genetic code into an amino acid sequence
Ribosome
The site of protein synthesis
Control the entry and exit of materials in discrete organelles
Separate organelles from cytoplasm so that specific metabolic reactions can take place
Intracellular
Provide an internal transport system, e.g. endoplasmic reticulum
membranes
Isolate enzymes that might damage the cell, e.g. lysozymes
, 6
CELL STRUCTURE
Provides a semi-permeable membrane between the cell and its external environment
Controls movement of substances in and out of the cell
Cell surface
Involved in cell-cell adhesion
membrane
Contains numerous proteins which serve as pores, pumps, receptors and signalling
molecules
Controls the shape of the cell, allows it to move and provides tracks which proteins
organelles can move along
Provides structural support for the cell, maintaining its shape and providing anchorage
Cytoskeleton for organelles.
Organises structures and activities of the cell
Involved in signalling between cells
Involved in the sorting and delivery of internalised material from the cell surface and
Endosome the transport of materials from the Golgi to the lysosome
Secretory Cell secretions – e.g. hormones and neurotransmitters – are packaged in secretory
vesicles at the Golgi apparatus. The secretory vesicles are then transported to the cell
vesicles surface for release
, 7
Golgi
Apparatus
.
.
,8
, 9
PARAMETERS LIGHT MICROSCOPY ELECTRON MICROSCOPY
Size Small and portable Large and static
Cost Relatively cheap Expensive
Radiation type Light Electrons
Magnification X1500 X500 000
Resolution 250nm 0.25nm
Control of image
Glass lenses Electromagnets
formation
Type of material
Living/moving/dead/abiotic Dead/abiotic
that can be viewed
Image colour Can see colours/might need staining Black and white/requires staining
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