cell structure Flashcards
what is the cell theory
- cells are the smallest unit of life
- all cells come from pre-existing cells
- living organisms are composed of cells
what organelles/cellular components are visible under the light microscope
nucleus, chloroplast, cell wall, flagella, plasma membrane (in plasmolysed cells)
what are the membrane-bound organelles
nucleus, ERs, Golgi apparatus, lysosome, mitochondrion and chloroplast
what are the non-membrane organelles
ribosome and centriole
describe structure of nucleus
spherical
surrounded by nuclear envelope which is a double membrane - perforated with nuclear pores and continuous with rough ER
contains nucleolus and chromatin
functions of nucleus
- contains hereditary material DNA
- controls cell activities by regulating protein synthesis
- contains enzymes for DNA replication, transcription and RNA processing
structure of nucleolus
non-membranous, a sphere within the nucleus
contains large amounts of DNA, rRNA and protein
dense and stains dark
function of nucleolus
- synthesises rRNA
- site of assembly of rRNA and proteins into large and small ribosomal subunits - uses rRNA synthesised in nucleolus and proteins exported from cytoplasm
function of chromatin
contains genes: undergo transcription in nucleus = forms mRNA - then undergoes translation at ribosomes = forms polypeptides
structure of rough endoplasmic reticulum
network of membranous flattened sacs (cisternae_
has ribosomes bound to outer surface (‘bound’ ribosomes)
continuous with outer membrane of nuclear envelope
function of RER
- transports proteins which are synthesised by bound ribosomes to Golgi apparatus via transport vesicles
- allows proteins to fold into their native 3D conformation in the cisternal space
- glycosylation in cisternal space: glycosylates proteins to form glycoproteins
structure of smooth ER
network of membranous tubular sacs (cisternae)
lacks ribosomes on outer surface = smooth
function of SER
- synthesises lipids and carbohydrates
- abundant in liver: to detoxify drugs and poisons
- special SER called sarcoplasmic reticulum stores Ca2+ ions
structure of Golgi apparatus
membrane bound flattened sacs (cisternae) and associated Golgi vesicles
has a cis face: where transport vesicles from ERs fuse to = forms new cisternae
and a trans face: where Golgi vesicles continuously bud off from
function of GA
- Glycosylation: carbohydrates are added to proteins and lipids to form glycoproteins and glycolipids respectively;
- Modification* of existing glycoproteins and glycolipids by modifying/cleaving existing sugar chains
- In plant cells: the site for synthesis of polysaccharides such as pectin = then transported in vesicles to the cell membrane;
- Sorting and packaging* of proteins into different kinds of vesicles = targets and transports proteins to different parts of cell or for secretion out the cell
- Formation of lysosomes* which contain hydrolytic enzymes within them
structure of lysosome
membranous sac containing hydrolytic enzymes
contains an acidic environment for the enzymes
destroys cell if many lysosomes burst
pH of cytosol remains neutral if one lysosome bursts
function of lysosome
- in endocytosis: digest material taken in by cell by phagocytosis
- release enzymes from cells by exocytosis for extracellular digestion
- autophagy: digest unwanted/worn-out organelles
- autolysis: self-destruct a cell after its death
structure of ribosome
consists of a small and a large subunit - each subunit is made up of protein and rRNA is assembled in the nucleolus - only come tgt in translation
either freely floating in cytosol or bound to ER
function of ribosome
site for protein synthesis
1. bound ribosomes: synthesises proteins meant for insertion into membranes/packing within organelles/secretion out of the cell
2. free ribosomes: produce proteins that function within cytosol
structure of centriole
a pair of hollow cylinders made up of 9 triplets of microtubules each
positioned at right angles to each other
found in the microtubule organising centre found in the centromere
structure of microtubule
hollow tubes made of the protein tubulin
function of microtubules
- maintain the shape of cells - act as cytoskeleton
- microtubules: direct movement of transport vesicles and secretory vescicles to GA and cell surface membrane respectively
- make up the spindle fibres
- form structural component of centrioles, cilia and flagella
function of centriole
(includes microtubules)
- organises spindle fibres during nuclear division
- determines polarity of the cell
3.
describe endomembrane system
- DNA is used as a template to synthesise mRNA in the nucleus
- mRNA leaves nucleus via nuclear pores
- mRNA is used as a template to synthesise polypeptides on ribosomes on the RER
- polypeptides enter lume of cisternae of RER = folded into its tertirary conformation to form a protein = undegoes glycosylation.
- transport vesicle containing proteins buds off from RER and carries proteins to GA
- vesicle fuses with cis face of GA = releases proteins
- protein undergo futher modification, sorting anf packing
8.secretory vesicle containing the modified protein buds off trans face of GA = transported to and fuses with CSM - protein content of vesicle released by exocytosis - requires ATP
similarities between chloroplast and mitochondria
- Both are bound by a double membrane. Outer membranes are not folded;
- Inner membrane encloses a fluid-filled cavity (i.e. stroma in chloroplast & matrix in
mitochondrion); - both fluid-filled cavities contain 70S ribosomes;
- and contain circular DNA strands and enzymes e.g. DNA polymerase and RNA polymerase;
- ATP synthase(stalked particles) are found in both organelles.
differences between chloroplast and mitochondria
- size: larger vs smaller
- shape: discoid, biconvex vs spherical
- inner membrane: not folded and do not contain ATP synthase vs extensively folded with inner portion of membrane containing ATP synthase
- granules present: starch vs phosphate
- internal membrane system: present (in the form of stacks of thylakoids) vs absent
- location of atp synthase: on thylakoid membrane vs inner membrane
- presence of coloured pigments: present (photosynthetic pigments) vs absent
- arrangment of inner membrane: not arranged into folds vs arranged into folds known as cristae
