cell biology Flashcards
discovery of the cell
1665, Robert Hooke looked at thin slice of cork through two-lens microscope
cell theory
- Schwann proposed ‘cell theory’
-> all organisms made of one or more cells
-> cell is basic unit of life; it is smallest unit that shows all characteristics of life
-> all cells come from pre-existing cells (i.e. process of cell division)
cytosol
jelly-like material in which organelles ‘float’
if organelles removed, soluble part that would be left is called the cytosol
mainly made of H2O
chemical reactions i.e. cellular signalling and glycolysis
nucleolus
spherical body inside the nucleus
becomes enlarged during protein synthesis
contains DNA templates for rRNA transcribed by RNA pol I
synthesize and assemble ribosomes
nucleus
contains DNA in the form of chromatin
surrounded by nuclear envelope which is a double membrane
- continuous with interior of RER
~3000 nuclear pores, regulated by protein structure
- large molecules strongly regulated
mitochondria
oxidative phosphorylation
- enzymatic oxidation of cell metabolites is converted into ATP
- uses electrons from biochemical reactions (NADH donates)
- needs ATP synthetase: H+ gradient generates ATP
endosymbiotic theory
mitochondria were primitive bacterial cells
mitochondria and eukaryotes become mutually benefit
permanent dependent relationship
have own circular DNA exclusively from mother
endoplasmic reticulum
forms interconnected network of tubules vesicles and cisternae within cells
site of protein synthesis and packaging of cell chemicals into transport vesicles
smooth ER
- synthesis of membrane lipids and steroids
- more prominent in:
-> cells of adrenal cortex (secrete steroid hormone)
-> hepatocytes where it synthesizes lipids for secretion of lipoproteins
-> sarcoplasmic reticulum of muscle cells is SER
rough ER
- has ribosomes on external cytoplasmic layer of ER and translate mRNA into protein
golgi apparatus
stacks of membrane-bounded cisternae located between ER and cell surface
main job processing protein synthesised in RER (packaging and shipping)
vesicular enzymes modify ( i.e. glycosylate) and transport molecules in cells for e.g. exocytosis
central dogma of molecular biology
all cells contain the same DNA
genes encode for proteins
- made of linearly arranged amino acid residues
central dogma of molecular biology
all cells contain the same DNA
genes encode for proteins
- made of linearly arranged amino acid residues
extracellular matrix
proteins exocytosed into the extracellular space
often referred to as connective tissue
comprises high quantities of fibrous proteins i.e. collagen
endocytosis (take it up)
cell membrane invaginates, pinches in, creates vesicles enclosing contents
exocytosis (get it out)
membrane vesicles fuses with cell membrane, releases enclosed material to extracellular space
cytoskeleton
extensive network of protein fibres
functions in:
- providing mechanical strength - myosin and actin muscle contraction
- locomotion, remodelling - move organelles around cell
- chromosome separation in mitosis and meiosis
- intracellular transport of organelles
- cellular signalling
microfilaments
- linear polymer of actin subunits
- flexible and string, resting buckling and filament fractures
microtubules
- conveyer belts inside the cells
- move vesicles, granules, organelles like mitochondria and chromosomes
- linear polymers of tubulin
intermediate filaments
- withstand mechanical stress
focal adhesions (attachment complexes)
- attachment complexes anchor contractile filaments to cell membrane
- comprise at least 150 proteins components
- inc many structural, enzymatic and proteolytic enzymes
ribosomes: mRNA translation
ribosomes made of protein and rRNA
ribosome clamps over tRNA and mRNA to make new protein
- A site received new tRNA
- P site receives peptide-bearing tRNA after peptide bond formation
- E site is where tRNAs exit
4 major proteolytic systems
cells need to constantly synthesise and degrade proteins
lysosomes - ‘bulk’ protein breakdown
- they are created by the addition of hydrolytic enzymes to early endosomes from the golgi apparatus
- these enzymes work best at low pH (~5)
-> proteins in the lysosomal membrane pump hydrogen ions from the cytosol to the lumen of the lysosomes
- the lysosomes create a space where the cell can digest molecules (proteins, fats, nucleic acids etc) safely
ATP-dependent ubiquitin proteasome- protein breakdown
- breakdown of ‘tagged’ cellular proteins
- essential part of normal cell turnover (and thus health)
calpains and caspases
- calpains are calcium activated degradative proteins
-> cleave and break down proteins when elevated calcium levels
- caspases cleave and degrade proteins
peroxisomes
- membrane bound enzyme sacs
- oxidation reactions produce h2o2
- catalase converts h2o2 -> h2o or uses it to oxidize another organic compound
- various energy substrates broken down by oxidative reactions in peroxisomes inc uric acid, amino acids and fatty acids
cell membrane: fluid mosaic model
hydrophilic head groups separate hydrophobic tails from aqueous cytosolic and extracellular environments
membrane transport (selectively permeable)
osmosis
- diffusion of water across semi-permeable membrane (low solute conc to high solute conc)
- aquaporins
simple diffusion
- no channels
facilitated diffusion
- assisted membrane proteins
active transport pump and carriers
- requires energy
- primary and secondary transport
- coupled transport
- one ion down electrochemical gradient AGAINST conc gradient
- energy supplied by electrochemical gradient
hypertonic solution
fluid greater conc solutes than inside cell
inside -> outside
isotonic solution
same conc of solutes
no net movement
hypotonic solution
fluid lower conc solutes than in the cell
outside -> inside cell
membrane potential and active transport
resting membrane potential
cell more permeable to K+ than Na+
Na+/K+ active transport
- ATP hydrolysis transport Na+ out of cell and K+ into cell both against conc gradients
signalling molecules
cells constantly receiving info to control and regulate their activities
cells communicate to others to control and regulate systems
molecules that communicate with other cells called signalling molecules/ ligands
signal transduction
act on chemical signal so must have receptor
information then processed to produce appropriate cellular response
may involve several steps called signal transduction pathway
responses to signals
activation of genetic material (DNA)
lead to production of proteins
enzymes in range of metabolic reactions
production of another hormone and carry signals to other cells
or may supress production of proteins inc enzymes and down-regulate particular metabolic reactions
