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