2a (cell structure/division) Flashcards
Describe the structure and function of the nucleus.
Surrounded by nuclear envelope with nuclear pores. Contains dna and histone complex (chromatin) and the nucleolus which makes rna which is made into ribosomes that move out of cell and attach to rough er
Describe the structure and function of the chloroplasts.
Small, flat, double membrane. Filled with stroma (liquid) and grana (stacks of thylakoids linked my lamellae). Site of photosynthesis.
Describe the structure and function of the mitochondria.
Double membrane. Inner layer folds to form cristae which project into matrix which has enzymes for resp.
Describe the structure and function of the ribosomes.
Tiny, in cytoplasm/ attached to rough er. Made of protein and rna. Site of protein synthesis.
Describe the structure and function of the Golgi apparatus.
Fluid filled, membrane bound flat sacs. Process and package lipidsand proteins.
Describe the structure and function of the Golgi vesicles.
Fluid filled sac in cytoplasm, surrounded by membrane, made by apparatus. Store and transport.
Describe the structure and function of rough ER.
Membrane bound sacs (cisternae). Studded with ribasomes. Folds and processes proteins.
Describe the structure and function of smooth ER.
Membrane bound sacs (cisternae). Synthesises and processes lipids.
Describe the structure and function of lysosomes.
Round organelle surrounded by membrane. Type of vesicle. Contain lysozymes which digest invaders/ worn out parts.
Describe the structure and function of the cell surface membranes.
Made of lipids and proteins. Regulates movement of substances in and out of cell. Receptor molecules on it respond to chemicals.
Describe the structure and function of the cell wall.
Rigid structure surrounds plant,algae (cellulose) and fungi (chitin). Supports shape. Has plasmodesmata (pores) allow exchange/ transport.
Describe the structure and function of the vacuole.
Just plants (animal may have temporary). Filled with cell sap (watery solution of water sugar enzymes etc) surrounded by membrane called tonoplast. maintains cells pressure and rigidity stops wilting.
Describe the structure and function of the centrioles.
Just in animals. Self replicating organelles made of 9 bundles of microtubules. May help organise cell division.
Describe the structure and function of the cilia and flagella.
Single cell eukaryotes- essential for locomotion
Multicellular organisms- cilia move fluid/ materials past immobile cells and move cells
How are intestinal epetherial cells adapted for their function?
Microvilli- large sa for absorption
Mitochondria- energy for absorption
How big are ribosomes in prokaryotic cells compared to eukaryotic?
Smaller
What is a flagellum?
long hair like structure that rotates so the prokaryotic cell can move. some have none some have multiple
What is circular dna?
long coiled up strand of dna free in the cytoplasm and not associated with any proteins.
what are plasmids?
small loops of dna not part of the main circular molecule. contain genes for antibiotic resistance etc and can be passed between prokaryotes. not all prokaryotic cells have them.
what is a slime capsule?
helps protect (mainly bacteria) from attack from immune system cells. not all have one
what is a prokaryotic cell wall made of?
murein which is a glycoprotein (protein with carbohydrate attached)
What is a prokaryotic cell?
a cell that lacks membrane bound organelles and is much smaller than a eukaryotic cell
How do prokaryotic cells replicate?
binary fission
what does binary fission involve?
- circular and plasmid dna replication (circular once but plasmid lots)
- cells get bigger and dna moves to opposite poles
- cytoplasm divides and cell wall begins to form
cytoplasm divided in 2 creating daughter cells with 1 copy of circular dna and varied no of plasmids
what is a virus?
examples?
acellular and non living- just nucleic acids surrounded by proteins
HIV causes AIDS, influenza virus causes flu and rhinovirus causes cold
Describe the structure of a virus
what does each part do?
a core of genetic material (dna or rna) surrounded by a capsid (protein coat) which protects genetic material with attachment proteins that allow virus to identify and attach to host cells
describe viral replication
Viruses not alive so dont divide. They inject their nucleic acid into the host cell (after attaching to host with attachment complimentary to receptor proteins) , the infected host cell replicates the virus particles using its machinery (ribosomes, enzymes etc). the viral components assemble and leave the host cell.
How do you work out number of bacteria at end of divisions?
no at start x 2^no of cell divisions
What is magnification?
how much bigger the image is than the specimen
What is resolution?
the ability to distinguish between 2 points- mag doesnt increase it
(furthest away 2 objects can be for them to appear as separate items.
magnification=
image size / actual size
how does a light microscope work?
uses light to form image
light has long wavelength so lower resolution.
cant see ribosomes, er maybe mitochondria
max mag and res of optical microscope?
mag- 1500
res- 0.2 um
how does a transmission electron microscope work?
condenser electromagnets focus beam of electrons which is transmitted through specimen
denser parts absorb more electrons so appear darker vice versa
image appears on screen and can be photographed to produce photomicrograph
adv of transmission microscopes
high res (up to 0.1nm) so shows small objects
disadv of transmission microscopes
specimen thins so beam can pass
nonliving specimens-vacuum (so particles in the air dont deflect the electrons)
high energy electrons may damage specimen
2D and no colour (despite complex staining)
how does a scanning electron microscope work?
scans beam of electrons across surface of specimen knocking off electrons (so doesnt need to be thin) which are gathered in cathode ray tube to form and image. pattern of scattering depends on contours of surface- can build 3D image by computer analysis of pattern of scattered electrons
adv of scanning microscope
thick specimens can be used
3D
disadv of scanning microscope
low res (20nm)
nonliving specimens- vacuum
no colour despite staining but false colour can be added
less effective at showing inside of cell
how do you prepare a microscope slide?
drop of water on slide
prepare thin layer of tissue (so light can pass)
add stain (eosin for cytoplasm or potassium iodide for starch in plants)
add coverslip carefully with mounted needle to avoid air bubbles.
What is an artefact?
something you can see down a microscope that isnt part of cell/specimen youre looking at- can be dust, air bubbles, fingerprints etc
usually made during preparation so common in electron micrographs which take a lot of prep
how did scientists realise artefacts werent part of cell?
prepared specimen differently and if object seen sometimes not others then likely to be an artefact
describe the 3 stages of fractionation
1) homogenisation to break plasma membrane and release organelles. blend/ grind with cold isotonic buffer solution
2) filter homogenate through gauze to remove whole cells and debris
3)ultracentrifugation- spin heaviest organelles form pellet so pour off supernatant and spin it again at faster speed then keep repeating
what is cell fractionation?
separating organelles from cells
why do you use a cold, isotonic buffered solution
cold- reduce enzyme activity of enzymes that break down organelles. stops autolysis
isotonic- organelles dont gain/lose water through osmosis casing damage
buffered- maintain pH so proteins dont denature
what order do organelle pellets form in?
nuclei, chloroplast, mitochondria, lysosomes, endoplasmic reticulum, ribosomes
what is mitosis and what is it needed for?
Mitosis is the part of the cell cycle in which a eukaryotic cell
divides to produce two daughter cells, each with the identical
copies of DNA produced by the parent cell during DNA
replication. needed for growth and repair of tissues (replacement of cells)
cell cycle order
interphase, {prophase, metaphase anaphase, telophase}, cytokinesis
what happens in interphase?
cell carries out normal functions but prepares to divide
G1- cell grows, organelles replicated, cytoplasm increases
S- dna unravelled and replicated, 2 copies remain joined at centromere
G2- checks for errors, proteins synthesised
ATP content increases for division
what happens in prophase?
chromosomes condense, shorten, thicken so visible
centrioles (tiny bundles of protein)move to poles and form spindle fibres
nucleolus disappears, nuclear envelope breaks down and chromosomes free in cytoplasm
what happens in metaphase?
chromosomes line up across equator and spindle fibres attach from centriole to centromere
what happens in anaphase?
centromere divides in 2 separating sister chromatids
spindle fibres contract pulling chromatids to opposite poles (centromere first so v shaped)
energy from mitochondria gathered at spindle fibres
what happens in telophase?
chromatids have reached poles and uncoil to become long and thin and not visible- now called chromosomes
spindle fibres disintegrate, nuclear envelope forms around each group of chromosomes
what happens in cytokinisis?
cytoplasm divides so now 2 genetically identical daughter cells
What is cancer?
uncontrolled cell division forming a tumour. Cancer is a tumour that invades surrounding cells
what is the proto-oncogene?
what happens when it mutates?
gene that helps cells grow
mutates to become oncogene which is permanently switched on so cells grow out of control
what is the tumour supressorgene?
what happens when it mutates?
slows down cell division, repairs dna mistakes, tells cells when to die
when doesnt work properly, cells grow out of control
some cancer treatment disrupts cell cycle. 3 examples?
1) interphase- dna cant replicate
G1- prevent enzyme synthesis
needed for dna replication so cant
enter s phase and kills itself
S- damage dna so if detected, killed
2) metaphase- spindle fibre doesnt form
properly and attach to centromere
3) anaphase- prevents spindle fibres
contracting
Problems with cancer treatments?
Treatments kill all cells dividing but tumour cells divide more frequently so more likely to kill them.
drugs target rapidly dividing cells but some normal body cells rapidly divide such as hair producing cells.
Mitotic index =
no of cells with visible chromosomes / total number of cells
