cell structure Flashcards
cell-surface membrane (eukaryotic cells)
- phospholipid bilayer
- function –> extracellular substances enter & waste leaves the cell (sometimes requires active transport or membrane proteins)
smooth endoplasmic reticulum
- (membrane forms flattened sacs –> called cisternae)
- site of lipid synthesis, toxin modification & glycogenesis
rough endoplasmic reticulum
- (membrane forms flattened sacs –> called cisternae)
- has large no. of ribosomes attached to the surface
- folds & processes proteins made on the ribosomes
nucleus
(eukaryotic cells)
- nuclear envelope has a double membrane & nuclear pores to export mRNA n ribosomes into cytoplasm
- contains chromatin –> consists of DNA bound to histone proteins
- contains nucleolus –> site of ribosome production
ribosomes
-either free or on R.E.R
-eukaryotes have 80s ribosomes –> consists of 2 subunits, 60s & 40s
-70s ribosomes found in prokaryotes, mitochondria & chloroplasts
-site of translation (during protein synthesis)
golgi apparatus
(eukaryotic cells)
- stack of membrane-bound flattened sacs
- proteins modified in cis-face
- role in ‘packaging’ & ‘secretion’ of proteins
- digestive enzymes placed into lysosomes
golgi vesicles
(eukaryotic cells)
export modified proteins to fuse with the cell membrane (leave through trans-face)
mitochondria
(eukaryotic cells)
- site of aerobic respiration
- double membrane
>inner membrane folds to form cristae (gives it large S.A –> increases rate of aerobic resp.) - small circular pieces of DNA found in the matrix
centrioles
(eukaryotic cells)
- hollow cylinders
- produce spindle fibres for cell division
lysosome
(eukaryotic cells)
- small, membranous vehicle
- has hydrolytic enzymes –> destroys pathogens/gets rid of unwanted cells & organelles
vacuoles (only in plant cells)
- membrane-bound organelle found in all plant cells
- surrounded by tonoplast
- turgid –> helps cells stay rigid
chloroplasts (only in plant cells)
- site of photosynthesis (light-dependant stage takes place in the thylakoid membranes, light-independant stage takes place in the stroma)
- membrane-bound thylakoids containing chlorophyll stack to form grana
–> grana joined tg by lamellae
plant cell wall
- provides structural support (made of cellulose)
- plasmodesmata (narrow threads of cytoplasm) connect the cytoplasm of neighbouring plant cells)
epithilial cell
(specialised eukaryotic cell)
- villi increase S.A for absorption
- mitochondria releases energy to waft things away/transport digested food molecules
erythrocyte
(specialised eukaryotic cell)
no nucleus & biconcave disc shape –> maximises S.A –> can carry more oxygen
sperm cell
(specialised eukaryotic cell)
- acrosome enzyme to penetrate egg
- long midpiece –> lots of mitochondria –> releases lots of energy for swimming
how is bacteria digested?
(exam q)
lysosomes fuse with the vesicle & release hydrolytic enzymes
organelles in prokaryotic cells
1) plasma membrane
2) peptidoglycan cell wall
3) capsule (outer gel coating)
* flagella
* pili (for attachment to other cells, involved in reproduction)
* plasmid DNA
* circular DNA
* ribosomes (not membrane bound!!)
what is the name for the types of organelles eukaryotic cells contain but prokaryotic cells don’t contain?
membrane-bound organelles!
difference between DNA in eukaryotes & DNA in prokaryotes
- eukaryotes –> linear, long, associated w histone proteins, contains introns
- prokaryotes –> circular, short, not associated w histone proteins, no introns
parts of virus particle
-attachment proteins
-genetic material
-capsid
process of viral replication
- virus injects nucleic acid into host cell
- infected host cell replicates the virus
process of binary fission
- circular DNA & plasmids replicated in bacterial cell
- circular DNA & plasmids move to opp. poles of cell
- cytoplasm divides
- two daughter cells prod. –> each contains 1 copy of circular DNA (but can have multiple plasmids)
define ‘resolution’
minimum distance at which 2 very close objects can be distinguished
light microscope –> preparation
- cut thin layer of specimen
- add drop of water & potassium iodide/stain onto specimen
- put coverslip on top
light microscope –> pros
- images are colourful
- living tissue can be viewed
light microscope –> cons
- long wavelength of light makes resolution low
- max. magnification only x1500
scanning electron microscope
- beam of electrons scatters across surface of specimen, knocking electrons off –> electrons form 3D image
- lower resolution than TEM (but higher than optical)
transmission electron microscope
- beam of electrons passes through specimen
–> areas that absorb electrons = darker on micrograph
–> internal image prod.
electron microscopes –> cons
- in vacuum environment –> living objects can’t be viewed
- specimens must be very thin
- specimens must be dehydrated & stained w heavy metals
- complex staining process may intorduce artefacts
why do electron microscopes have a vacuum environment?
so particles in the air don’t deflect electrons out of the beam alignment
define ‘cell fractionation’
technique which separates organelles according to their density
stages of cell fractionation
- homogenisation
- filtration
- ultracentifugation
homogenisation
place cells in cold, isotonic & buffered solution –> blend to release organelles
* cold –> reduces enzyme activity as some enzymes may break down organelles
* isotonic –> solution needs same w.p as organelles so osmosis doesn’t occur (organelles would burst/shrink)
* buffered –> maintains constant pH (proteins in organelles can be denatured by change in pH)
filtration
removes any tissue debris
ultracentrifugation
- filtrate spun at diff. speeds
- heaviest organelles sink to bottom of tube, forming pellet
- fluid above the supernatant is removed and spun again in centrifuge at higher speed
- process continues until desired organelle is obtained
(nuclei would be 1st, ribosomes would be last)
stages of cell division
- interphase
- mitosis
- cytokinesis
interphase
- G1 –> protein synthesis
- S –> DNA replication
- G2 –> DNA checked over
mitosis
- prophase –> chromosomes condense & become visible, spindle fibres form, nuclear membrane breaks down
- metaphase –> chromosomes line at up equator & attach to the spindle fibres via centromere
- anaphase –> spindle fibres contract, centromere splits, sister chromtids pulled to opp. poles of cell
- telophase –> nucleus begins reforming
cytokinesis
2 gentically identical, diploid cells produced
what is mitosis used for?
- growth & repair
- asexual reproduction
