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Summary 4BBY1030- Cell Biology and Neuroscience
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4BBY1030- Cell Biology and NeuroscienceL2: Cell Types and Sub cellular Structures
• There are 3 main points to cell theory:
• All living organisms are made up of one or more cells.
• The cell is the basic unit of life.
• Cells arise from pre existing cells by division.
• Prokaryotes have no nucleus and are always single celled. They include bacteria, including
cyanobacteria and archaea which are adapted to live in extreme environments.
• Eukaryotes have a nucleus and can be single or multicellular.
• It is assumed that all cells are derived from a common ancestor.
• The plasma membrane has 4 main roles: to act as a barrier, communication, import and export
and as an electrical capacitor.
• The cytoskeleton has several major roles, including maintenance of shape/stability, adaptation
of shape, cell division, motility and movement of particles within cells.
• Cytoplasm is an aqueous solution with a pH of 7.2. It contains ions, a high concentration of
proteins, tRNA’s, free ribosomes and inclusion bodies.
• The nuclear envelope is a double membrane which contains the nucleoplasm, chromosomal
DNA and packaging proteins (histones) and gene regulatory proteins.
• The nucleus is the site of ribosome synthesis and can capture gene regulatory proteins.
• The endoplasmic reticulum is a network of interconnected membrane vesicles (cisternae) and is
continuous with the outer nuclear membrane.
• The rER is the site of synthesis for secreted and transmembrane proteins and has ribosomes.
• The sER is the site of synthesis for lipids and steroid hormones detoxification of the liver and
release of glucose from the liver.
• The golgi apparatus is a stack of flattened membrane vesicles, used for the modification of
proteins desired for secretion as well as transmembrane proteins.
• The mitochondria makes up 25% of the cell. It has a double membrane called the cristae.
• It contains circular DNA (mtDNA) and ribosomes in the matrix which gives it an alternate genetic
code.
• Mutations in mtDNA defects nuclear genes that code mitochondrial proteins, which is passed
down through mothers.
• Lysosomes degrade unwanted protons and particles taken up by the cell, and membranes and
organelles which are no longer needed.
• Peroxisomes degrade fatty acids and toxic compounds. The oxidation of fatty acids produced
precursors for biosynthetic pathways.
• Oxidation produces H2O2 which is harmful. Catalase neutralises this:
, L3: Cells in their environment
• It is believed that the last common ancestor of cells lived in an environment containing HCHO,
HCN, cyanide, gylceraldehyde, PO43- etc.
• The theory is that simple chemicals formed RNA (which can store info) through catalysis. They
folded into ribozyme complexes which had catalytic activity, and eventually developed into DNA
as well as lipid bilayers to spontaneously form vesicles.
• Photosystem I and II developed independently and are now part of photosynthesis which further
supports the endosymbiotic theory.
• Single celled eukaryotes are called protozoans.
• Embryogenesis requires tight control of cell division, morphogenesis and differentiation.
• Somatic cells are differentiated and mortal whereas germ cells are gonidia (asexual),
reproductive and immortal. They were both present in the first organisms.
• Outside of the host cell a virus is known as a viron. It consists of DNA/RNA, capsid, and
sometimes a lipid envelope.
L4: Cytoskeleton
• There are 3 types of cytoskeleton, actin, intermediate and microtubules.
• Because of the motor activity of myosin, myosin filaments slide on actin filaments causing
muscle contraction.
• Main functions of actin on non-muscle cells include defining their shape and structure, allowing
them to change shape and move, and allowing them to exert contractile force (cleavage furrow).
• Stress fibres are contractile actomyosin bundles in the cytoplasm.
• Lamellipodium is a thin, sheet like extension which contains a meshwork of actin filaments.
• Filopodium are spiky, transient protrusions made by actin monomers.
• Actin filaments are polymers made by actin monomers and undergo dynamic polymerisation-
depolymerisation cycles. They can also be severed, cross-linked etc.
• Keratin (only in epithelial cells) is a protein that can form intermediate filaments which are multi-
stranded fibres with a coiled structure. They strengthen cells against mechanical stress.
• The nuclear lamina is the intermediate fibre which gives structural support to the nuclear
envelope. These are broken down during cell division to allow spindle fibres to access the
chromosomes.
• Microtubules are the main components of spindle fibres (13 = 1 fibre). They also form the shaft
in cilia and propel their beating, similar to sperm tails.
• Microtubules form a network in the cytoplasm to help move organelles.
• The dynamic instability of them allows for their efficient remodelling.
• Diverse regulatory proteins control the dynamics and function of microtubules.
• Motor proteins travel on microtubules using energy. Kinesins move towards the +ve side and
dyreins move to the -ve side. They also allow transport in the neuron across the axon.
L5: Extracellular matrix, cell adhesion and cell junctions
• There are two types of extracellular matrices. The basement membrane/basal lamina underlies
all epithelia and surrounds some non-epithelial cell types. It is mainly composed of collagen IV,
laminin, nidogen and perlecan.
• The fibrillar matrix is composed of many fibres in the mesenchyme, and is where cells such as
fibroblasts are buried. It’s mainly composed of collagen I, fibronectin, elastin and proteoglycans.
• Cell junctions are structures that enable cell adhesion, known as junctional complexes.
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