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Molecular cell biology


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what is cell theory?
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cell theory is that the cell is the structural unit of life that contains metabolic and genetic elements. cells can only arise by division of a preexisting cell. Modern cell theory is that energy flow occurs in cell, heredity information is passed from cell to cell and that all cell have the same basic chemical composition.

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What is cell theory?
Cell theory is that the cell is the structural unit of life that contains metabolic and genetic elements. cells can only arise by division of a preexisting cell. Modern cell theory is that energy flow occurs in cell, heredity information is passed from cell to cell and that all cell have the same basic chemical composition.
What are the two major cell types and what makes them different
Prokaryotes have circular DNA free in the cytoplasm, Eukaryotes have a 'true nucleus' linear DNA molecules held in a membrane bound nucleus, contain subcellular organelles to compartmentalise
Subdivisions of prokaryotes?
Bacteria and eubacteria
Where is dna located in prokaryotic cells, and how its structured
Nucleoid - not membrane bound, formed into a single loop and does not have introns, genes are grouped into operons
Describe the plasmid in a prokaryote
Small loops of non essential DNA and is smaller than genomic DNA. passes vertically during cell division or horizontally by bacterial conjugation. natural plasmids may carry antibiotic resistant genes. easil manipulated in vitro.
Describe the difference between vertical and horizontal transmission of plasmid
Vertical transmission is when a bacteria goes through binary fission (asexual reproduction), horizontal transmission involves conjugation.
What is conjugation?
Once replication of the plasmid is completed a donor will produce a pilus which makes contact with the recipient bacterium. pore in the membrane if formed to create a continuous conjugation tube. replic plasmid becomes linear and travels to the recipient where it becomes circular.
Ribosomes in prokaryotes
Free in cytoplasm (not attached to membrane), composed of protein and rRNA and function to translate mRNA to protein, sedimentation 70s.
Storage granules in prokaryotes
Store of carbon, either store glycogen or poly-ß-hydroxybutyrate but not both. Glycogen granules dispersed through cytoplasm visible when stained, poly-ß-hydroxybutyrate stains with the fat stain Sudan black
What are mesosomes?
Aggregates of tubular membrane structures, derived directly from plasma membrane
What are the internal membranes in prokaryotes
Lamellae, vescles or tubules, appearance in EM depends on bacteria type
What are bacterial microcompartments?
Protein shells filled with enzymes for key activities,carboxysomes help autotrophic prokaryotes fix carbon via calvin cycle, pdu are involved in propanediol utilisation
Plasma membrane in prokaryotes
Phospholipid bilayer embedded with proteins, do not have cholesterol which are replaced by hopanoids,stabalising membrane
Plasma membrane function
Contains cytoplasm and regulates movement of materials, site of cell wall synthesis, no mitochondria enzymes for energy gen need to be organised within plasma membrane
Outer membrane function
Gram neg, protects invading bacteria from host defence, essential nutrients pass via porins
Function of bacterial cell wall in prokaryotes
Resists internal osmotic pressure, prevents bursting in hypotonic media
What is in the cell wall
Peptidoglycan, strength is due to cross linking of peptide chains, prevents sugar units of polymer sliding over.
Capsule in prokaryote
Layer of polysaccharide and glycoprotein surrounding the bacteria
What is the periplasm
The space between peptidoglycan layer and the plasma membrane, filled with loose peptidoglycan network and enzymes for nutrient acquisition.
Flagellum in prokaryotes
Composed of flagellin low amounts of sulphur containing aromatic amino acids and high levels of aspartic and glutamic acid
What colour do gram negative and gram positive bacteria
Gram positive bacteria are purple, gram negative are pink what colour do gram negative and gram positive bacteria
Teichoic acid
Glycerol ribitol or manitol polymers in gram positive cell walls
Describe the gram negative cell wall
Thin layer of peptidoglycan,overlaid by a lipid layer similar to plasma membrane
Microbial diversity
Considers the vast array of microorganisms
What are acidophiles
Bacteria that can grow at a pH of 3 or below, they need to maintain a net outflow of protons to maintain the internal pH
What can acidophiles be used for commercially
Can be used to leach metals from low grade ores
What are alkalophiles
Bacteria that are inhibited by pH 8-9 or above, must maintain a net inflow of protons to preserve internal pH, example is Vibrio cholerae
What are the three groups of oxygen requirements for bacteria
Aerobes - depend on molecular oxygen facultative anaerobes - use oxygen if available anaerobes - cannot use oxygen
Aerobic bacteria
Found in terrestrial and aquatic habitats, don't grow in static liquid culture, require shaking
Facultative anaerobes
Commonly used andmedically significant E.coli, require fermentable sugars
Anaerobic bacteria
Some killed by oxygen (obligate),others are tolerant, depends on superoxide dismutase
What is the importance of superoxide dismutase
Destroys toxic superoxide radicals dormed during oxidation, converts superoxide radical to hydrogen peroxide and oxygen
Temperature - Psychrophiles
Grow well at 0 optimum near 15, found in arctic, membranes are high in unsaturated fatty acids
Psychotrophs
Grow at 0 but optimum is between 20-30, present in soil, cause of food spoilage
Mesophiles
Growth optimum around 20-40, majority are mesophiles, includes bacteria that live in association with or cause disease in animals
Thermophiles
Optimum about 55-65, grow in compost, enzymes and nucleic acids are heat stable, membrane lipids more saturated than mesophiles
Hyperthermophiles
Grow above 90, optimum between 80-113, includes species which grow in hot areas of ocean
Black smoker' bacteria
Grow in sulphide chimneys, grow at 113 '
Halophiles
Can tolerate high salt levels can colonise saline lakes, cell wall may be damaged from low salt concentrations
Are eukaryotes unicellular or multicellular
Eukaryotes can be both unicellular and multicellular
DNA molecules in Eukaryotes
Have linear DNA molecules packaged as chromosomes enclosed in nucleus, have membrane bound organelles
Unicellular eukaryotes
Most complex eukaryotes, perform all functions, unicellular when food available, when food is scarce they aggregate and specialise to form primitive multicellular organism
What are Eukarytotic cell membranes composed of
Phospholipids and protein, spontaneously assemble to form closed bilayers
Eukarytoic cell membranes: two faces
The two faces of the cell membrane are asymmetric in terms of lipid and protein composition Cytosolic face is the inner part, exoplasmic face is the outer part.
Functions of plasma membranes
Regulation of transport balance of chemical conditions chemical reaction site detects signals interacts with other cells/extracellular (multicellular)
Name the organelles of the eukaryotic cell
Nucleus, ER, golgi complex, mitochondria, lysosomes (ac), peroxisomes, cytosol, cytoskeleton
Nucleus
Contents are in contact with cytoplasm via nuclear pores which pass through both membranes Large dense region= Nucleolus, rich in protein and RNA
What does the nucleus separate
Separates DNA from the cytosol; transcription from translation
ER- two types and what they do
Extensive membrane structure forming interconnected sacs and tubules Rough ER= ribosomes attached to surface, plays role in synthesis of membrane-bound and secreted proteins Smooth ER = no ribosomes, plays role in producing lipids
ER
Lipid synthesis, membrane protein synthesis, Ca 2+ ion storage, detoxification Key features: interconnected closed membrane tubules and vesicles
Ribosomes
Multi-subunit structures, 50% protein, 50% ribosomal RNA rRNA key to structure and function of ribosomes synthesis of proteins 40s and 60s subunit= 80s
Mitochondria
Contains DNA and ribosomes, can direct production of some of own proteins self replicating = binary fission site of ATP production, aerobic metabolism, important role in apoptosis Key features: outer membrane intermembrane space inner membrane matrix
What is apoptosis?
Programmed cell death
Mitochondrial DNA
Genes exhibit cytoplasmic inheritance and encode rRNAs, tRNAs, mitochondrial proteins size and coding capacity of mtDNA varies products of mitochondrial genes are not exported mutations cause genetic diseases, leigh syndrome, optic neuropathy
Golgi complex
Stack of flattened membranous sacs vary in number sacs form from parts of rough ER which break off and fuse Inner face is close to the nucleus ensures that vesicles budding off outer face can fuse with plasma membrane packages lysosomal proteins and proteins to be secreted from cell
Lysosomes
Single membrane-bound organelles containing hydrolytic = degrade materials taken up by endocytosis and cell debris degrade damaged newly synthesised proteins
Peroxisomes
Single membrane-bound organelles contain catalase and urate ocidase = breaks down very long chain fatty acids via beta oxidation oxidation of toxins
Cytosol
Enclosed by the plasma membrane not static contents continuously moving key features: cytoskeleton polyribosomes metabolic enzymes
Cytoskeleton
Lattice like array of filaments and fine tubules involved in cell movement, division, maintenance, trafficking organelles 3 major components: microfilaments = actin microtubules intermediate filaments
Microfilaments
F-actin filaments are double helices of polymerised G-actin subunits fibres expand and contract by further polymerisation and depolymerisation, ATP dependent Interact with other filaments and 'motor' to create movement,contraction can cause shape change
Actin and myosin in Eukaryotic cells
Actin microfilaments work with myosin in muscle fibres myosin filaments walk along the tethered actin, pulling the filaments towards the centre to cause muscle contraction
Microtubules
Microtubules are polymers of tubulin that form part of the cytoskeleton tubes of tubulin: grow by polymerisation from specific microtubule organising centres microtubules can form trackways in cellsalong which motor proteins (kinesins) drag vescles, organelles. Play a fundamental role in partitioning of chromatids in cell divisions
Microtubules role in cell division
Partitioning of chromatids chromatids are one of two strands of a newly copied chromatid, two joined together at centrimere they are called sister chromatids and are genetically identical
Intermediate filaments
Different types that differ in composition and function, may have role in maintaining cell shape, tissue integrity
What are the specialised features of plant cells?
Chloraplasts, vacuoles and specialised peroxisomes plant cells have a rigid cell wall can communicate with eachother
Vacuoles
Make up 80% of plant cell store water, ions, nutrients, degrade macromolecules inflow of water by osmosis causes vacuole expansion and maintenance of turgor pressure expansion of vacuole involved in cell elongation
Chloraplasts
Double membrane bound, contain their own DNA Thylakoid membranes, fused into stacks in places, contains chlorophyll photosynthetic plant cells, contain chloraphyll to absorb light and generate NADPH and ATP
Specialised peroxisomes
Found in leaves involved in photorespiration (oxygen to carbon dioxide) Glyoxysomes found in germinating seeds, carry out glyoxylate cycle to convert fatty acids into sugars
Plant cell wall
Rigid cell wall comprised mainly of cellulose cross linked by hemicellulose, pectin, and lignin
Plasmodesmata
Directly connect the cytosol of adjacent cells in higher plants
Name the different tissues that cells that are organised into
Epithelia, nervous tissue, connective tissue, muscle, blood
Why are the layers of the early embryo important?
They give rise to the cell types, goes from xygote to blastocyst and then gastrula Germ cells = sperm or egg endoderm (internal) layer = lung alveoli, thyroid, pancreatic cell Mesoderm (middle) layer = cardiac muscle, skeletal muscle, tubule cell of kidney, RBC, smooth muscle. Ectoderm (External layer) = epidermis skin cells, neuron, pigmant cell.
Cells produced at 50-cell stage?
Cells that are produced at the 50- cell stage are called Embryonic stem cells, these cells are totipotent except foetal membranes)
What is totipotent?
Ability of a single cell to divide and produce all of the differentiated cells in an organism.
What is a pluripotent stem cell?
A pluripotent stem cells give rise to cells to a particular tissue
What is a monopotent stem cells
Monopotent stem cells can produce only one cell type
Can adult cells be reprogrammed?
Adult cells can be reprogrammed by manipulating the expression of key regulatory genes to produced induced PS cells, derived from blood or skin cells.
Differentiated cells
Differentiated cells express different subsets of genes: transcribed genes (transcriptome), and translated proteins (proteome).
Mechanism and Differentiation
Tissue specific gene expression is primarily regulated at the level of transcription, fine tuning at post-transcriptional and post-translation levels also occur. Signals received by the cell activate transcription factors to turn on certain genes. Inactive genes are characterised by methylation at CG doublets in their promoters
What are the four major classes of cell surface receptors
G-protein couples receptors Tyrosine kinase-linked receptors Ion channels receptors receptors with intrinsic enzymatic activity Singles generated at the plasma membrane are transduced to the nucleus via a complex series of secondary events
Name the secondary events in transducing signals from the plasma membrane
Binding of the second messengers to receptors and phosphylation
Apoptosis role
Has roles in embryogenesis, tissue homeostasis, damage limitation, control and functioning of immune system. Evolutionarily conserved and genetically controlled
What are the Two main gene families involved in apoptosis
Bcl-2 family (regulation) Caspase family (execution) Many accessory proteins - death domain proteins
Characteristics of apoptosis
Mild convolution, chromatin compaction, margination condensation of cytoplasm Breakup of nuclear envelope, nuclear fragmentation, Blebbing cell fragmentation Phagocytosis
Importance of Apoptosis
Too little apoptosis can lead to cancer, autoimmune diseases and prolonged viral infection Too much apoptosis leads to neurodegenerative diseases, autoimmune, tissue damage through trauma, progression of AIDS.
How does apoptosis become unregulated?
Genes controlling it become damaged or aberrantly expressed, inappropriate triggering of apoptosis, the interference by exogenous genes
Name cell types: Epithelia
Epithelial cells - from sheets that cover the inner and outer of the bodies surfaces Absorptive cells - have microvilli to increase their surface area ciliated cells - have cilia that beat to move substances over the sheet Secretory cells - secrete substances out onto the sheet
What are the main types of intestinal cells
Absorptive cells outnumbers others 10:1 Goblet cells: secrete mucous Paneth cells: secrete growth factors and antibacterial substances Enteroendocrine cells: secrete peptide hormones and serotonin into gut wall
Name 3 Neuron cell types
Neurons are specialised for communication, the axon conducts electric signals away from the cell body multipolar interneurons motor neurons sensory neurons
Cell types: rod cells, what are they?
Rod cells are specialised sensory cells in the retina, layers of disks contain light sensitive pigmant = rhodopsin Light evokes an electrical signal that is transmitted to the brain
Cell type: Erythrocytes, what are they?
Highly specialised, carry oxygen, protein component is haemoglobin loss of nuclei and internal membrane, cant replicate
Connective tissue, name some different connect tissues that arise from fibroblasts
Fills spaces between epithelial sheets and tubes Bone cell - osteoblasts/osteocytes Fat cells - adipocyte smooth muscle cell Cartilage cell - chondrocyte
What does fibroblast differentiation depend on
Depends on the etracellular matrix YAP and TAZ are transcription regulators that move to the nucleus in response to tension developed in the actin-myosin bundles in the cytoplasm
What does the transcription regulators YAP and TAZ stand for
YAP = yes associated protein TAZ = transcriptional coactivator with PDZ-binding motif
What are the different types of muscle cells
Cardiac muscle - in the wall of heart, adjacent cells connected by electrical conducting junctions to ensure synchronous contraction Skeletal muscle - striated muscle fibres, made from large multinucleated cells. control voluntary movement Smooth muscle - thin elongated cells non striated, control involuntary movement
What are the requirements for a multicellular organism
Interactions: Cell adhesion molecules tight junctions, gap junctions, adherens junctions Desomosomes Interactions between cells and their surroundings: Hemidesmosomes and focal adhesions basal lamina Extracellular matrix - integrity of tissues
Major classes of cell adhesion molecules
Homophilic interactions: Cadherins (E-cadherin) Ig-superfamily Heterophilic interactions: Integrins (alpha v beta 3) Selectins (P-selectin)
Tight junctions?
Sometimes cells need to form an impermeable barrier, tight junctions seal gaps between cells, the membranes are firmly pressed together and prevent leakage.