Cell Structure Flashcards
how do optical microscopes work
-light is directed through a thin layer of specimen that is supported on a glass slide.
-light is focused through several lenses
-use visible light having a wavelength of between 400nm and 700nm. therefore structures closer together than 200nm will appear as one object
what is the magnification on a light microscope
x1500
what is the resolution on a light microscope
limited, 200nm
what image does a light microscope produce
-photomicrograph
-2D
-coloured image
disadvantages of using a light microscope
small organelles e.g ribosomes cannot be seen.
2D
ribosome
very small, non membrane-bound organelles 20nm diameter, cannot be observed by light microscope
how does a laser scanning microscope work
-use laser light to scan an object point by point at different depths and assemble on a computer
-have depth selectivity
-specimen must be stained with fluorescent dyes.
-thick section of tissue is scanned
-laser beam is reflected by fluorescent dyes.
advantages of laser scanning microscope
-can be used on thick or 3D specimens
-allow external 3D structure to be observes
-very clear, high resolution images produced (even see structure of cytoskeleton in cells)
how does a TEM work
-use electromagnets to focus a beam of electrons
-beam of electrons is transmitted/passed through the specimen
-denser parts absorb more electrons (these parts appear darker on the final image)
advantages of TEMs
-high resolution images
-allows the internal structures within cells to be observed
disadvantages of TEMs
-thin sections only
-dead specimens only (due to vacuum)
-lengthly preparation treatment for specimens
-no colour
how does a SEM work
-send a beam of electrons across a specimen
-beam bounces off the surface of a specimen and electrons are detected
-produce 3D images that show surface of specimens
advantages of SEMs
-can view thick or 3D specimens
-allow the external, 3D structure to be observed
-colour can be added
how do optical microscopes work
-light is directed through a thin layer of specimen that is supported on a glass slide.
-light is focused through several lenses
-use visible light having a wavelength of between 400nm and 700nm. therefore structures closer together than 200nm will appear as one object
disadvantages of laser scanning microscopes
-slow process, takes time and expertise
-expensive
-can cause photodamage to cells.
disadvantages of SEMs
-lower resolution than TEM
-dead specimens only
-no colour naturally
magnification of TEM
x500,000
resolution of TEM
0.5nm
magnification of SEM
x500,000
resolution of SEM
3-10 nm
structure of nucleus
-surrounded by a double membrane (nuclear envelope)
-are pores in nuclear envelope
-contains chromatin (DNA wound around histone proteins)
function of nuclear envelope
separates contents of nucleus from rest of cell
function of nucleus
-control centre/ controls activities of cell
-stores genome
-transmits genetic info
-provides instructions for protein synthesis
function of nuclear pore
enable larger substances e.g messenger proteins to leave nucleus
structure of nucleolus
no membrane, contains RNA
function of nucleolus
site of ribosome production
structure of RER
-system of membranes (contain fluid-filled cavities=cisternae)
-coated with ribosomes
function of RER
-transport system
-large surface area for ribsomes (assemble amino acids into proteins)
structure of SER
-system of membranes (fluid filled cavities=cisternae)
-no ribosomes on surface
function of SER
-contains enzymes that catalyse reactions
-involved with absorption, synthesis and transport of lipids from gut.
structure of golgi apparatus
-stack of membrane bound flattened sacs.
-secretory vesicles bring material to and from GA
function of golgi apparatus
-modify proteins by:
-adding sugar molecules to make glycoproteins
-adding lipid molecules to make lipoproteins
-folded in their 3D shape.
-proteins packaged into vesicles that are pinched off are
-stored in cell
-moved to plasma membrane
structure of mitochondria
-spherical. rod shaped, branched
-2-5 um long
-inner part=fluid filled matrix
function of mitochondria
-site of ATP production during aerobic resp
-self replicating
-abundant in cells where much metabolic activity takes places, e.g liver cells
structure of chloroplasts
-large organelles 4-10 um long
-surrounded by a double membrane
-inner membrane=continuous with stacks of flattened sacs (thylakoids) which contain chlorophyll.
-fluid filled matrix=stroma
-contain loops of DNA and starch grains
function of chloroplasts
-site of photosynthesis
-contain chlorophyll: used to make ATP from light energy (occurs in the grana)
structure of vacuole
surrounded by membrane called tonoplast (contains fluid)
function of vacuole
-only plant cells have large, permanent vacuole.
-filled with water and solutes (maintains stability and turgidity of cell)
structure of lysosomes
-smaller bags, formed from golgi apparatus, each surrounded by a single membrane
-contain powerful hydrolytic (digestive) enzymes.
-abundant in phagocytic cell (such as neutrophils and macrophages)
function of lysosomes
-keep powerful hydrolytic enzymes separate from rest of cell
-can engulf old cell organelles, and foreign matter, digest them and return the digested components.
structure of cilia and undulipodia
-protrusions from the cell and surrounded by cell surface membrane.
-contains microtubules
-formed from centrioles
function of cilia and undulipodia
-epithelial cells have hundreds of cilia that beat and move the band of mucus
-most cells in the body have one cilium acting as an antenna. (contains receptors)
-only type of human cell to have an undulipodium is a spermatozoon. (undulipodium enables spermatozoon to move)
structure of ribosomes
-small spherical organelles- 20nm in diameter
-made of ribosomal RNA
-made in nucleolus
-some remain free in cytoplasm, some attach to ER
function of ribosomes
-ribosomes that are bound to ER=used for synthesising proteins.
-ribosomes that are free in cytoplasm are site of assembly of proteins used inside the cell
structure of centrioles
consist of 2 bundles of microtubules at 90° to each other (microtubules made of tubulin protein subunits)
function of centrioles
-before cell divides, the spindle, made of threads of tubulin, forms from centrioles.
-chromosomes attach to the middle part of the spindle and motor proteins walk along tubulin threads, pulling chromosomes to opposite ends of the cell.
-involved in formation of cilia and undulipodia:
-before cilia form, centrioles multiply and line up beneath the cell surface membrane.
-microtubules sprout outwards from each centriole, forming cilium and undulipodia.
structure of cellulose cell wall
-outside of plasma membrane
-made from bundles in cellulose fibres.
function of cellulose cell wall
-plant cell walls:
-provide strength and support
-maintain cell shape
-permeable
explain how to use an eyepiece graticule and stage micrometer to measure size of a structure
-place micrometer on stage to calibrate
-line up scales on graticule and micrometer. count how many graticule division are in 100um on the micrometer
-length of 1 eyepiece division = 100um / number of divisions
-use calibrated values to calculate actual length of structure
describe production and secretion of proteins
the nucleus produces mRNA. mRNA leaves the nucleus through the nuclear pore and attaches onto a ribosome on the rough endoplasmic reticulum (RER). the mRNA is translated by the ribosome and the ribosome synthesizes a protein. the vesicles are pinched off into and the protein is transported in the vesicles to the golgi apparatus. the protein is modified and packaged. the protein is pinched off into vesicles and is transported to the plasma membrane. protein fuses with the plasma membrane and the protein is released into the extracellular matrix
describe relationship between organelles involved in production and secretion of proteins
the ribosomes that synthesise proteins are attatched to the RER. the golgi apparatus, which modifies proteins for secretion, aligns with the RER
what are bacterial and fungal cell walls made of?
bacteria= peptidoglycan
fungi=chitin
explain role of cholesterol, glycoproteins & glycolipids in the cell-surface membrane
-cholesterol= steroid molecule connects phospholipids and reduces fluidity
-glycoproteins= cell signalling, cell recognition (antigens) & binding cells together.
-glycolipids= cell signalling & cell recognition.
structure and function of flagella
-hollow helical tube made of the protein flagellin
-rotates to propel (usually unicellular) organism
structure and function of cilia
-hairlike protrusions on eukaryotic cells
-move back and forth rhythmically to sweep foreign substances e.g. dust or pathogens away
cytoskeleton importance
-provides mechanical strength
-aids transport within cells
-enables cell movement
cytoskeleton importance
-provides mechanical strength
-aids transport within cells
-enables cell movement
organelles that both eukaryotic and prokaryotic have
-cell membrane
-cytoplasm
-ribosomes
contrast eukaryotic and prokaryotic cells
P=small & unicellular
E=larger, often multicellular
P=no membrane bound organelles & no nucleus
E=have organelles and nucleus
P=circular DNA not associated with proteins
E=linear chromosomes associated with histones
P=small ribosomes
E=larger ribosomes
P=binary fission (always asexual)
E=mitosis & meiosis (sexual/asexual)
P=cellulose cell wall (plants)/chitin (fungi)
E=no cell wall in animal cells, plants made of merein (peptidoglycan)
P=capsule, sometimes plasmids & cytoskeleton
E=no capsule or plasmids, always cytoskeleton
describe steps of protein synthesis
-ribosomes made in nucleolus
-mRNA made in nucleus
-ribosome attatches to ER
-mRNA leaves nucleus through nuclear pore and attaches to a ribsome on the RER
-ribosomes uses ‘instructions’ from mRNA to synthesise a protein
-protein folded/packaged/processed and travels via vesicles to the golgi
-fuses with golgi and protein is modified and packaged
-usually exported, vesicles transport to cell surface membrane, fuse and release proteins.
