Module 2 Section 1 - Cell Structure Flashcards
Pyper
cell ultrastructure
the internal structure of cells
plasma membrane description - what’s it made from?
aka cell surface membrane
mostly made of lipids & proteins
plasma membrane function
controls the movement of substances in and out of the cell
has receptor molecules on it which respond to chemicals (e.g. hormones)
cell wall function
supports plant cells
nucleus description
contains chromatin (made from DNA and proteins) and often a nucleolus
has a nuclear envelope and nuclear pores
nucleus functions (3)
- controls the cell’s activities
- contains DNA, which contains instructions to make proteins
- site of DNA replication and transcription (making mRNA)
nucleolus function(s)
makes ribosomes and site of rRNA production (which carries out protein synthesis)
nuclear envelope function
surrounds the nucleus
contains pores to allow substances to move between the nucleus and cytoplasm
RER description (2 parts - where is it found and what does it look like?)
rough endoplasmic reticulum
bound to the nuclear envelope
membrane-bound fluid-filled space
RER function
folds and processes the proteins that are made at the ribosomes
SER description
smooth endoplasmic reticulum
membrane-bound fluid-filled space, but not covered in ribosomes
SER function
synthesises and processes lipids and carbohydrates
lysosome description (2 parts - where’s it found?)
round organelle with membrane
only animal cells
lysosome function
contains digestive enzymes to digest invading cells or break down worn-out cell components
How do you spell the name of the organelle that contains digestive enzymes?
Lysosome
ribosome description (3 parts - where is it found and what’s it made of?)
- may flow free in the cytoplasm or is attached to RER
- not membrane-bound
- made of proteins & RNA
vesicle description
small membrane-bound fluid-filled sac
vesicle function
transports substances in and out of the cells and between organelles
Golgi apparatus description
group of fluid-filled, membrane-bound flattened sacs
small circles (vesicles) often found at the edges of the sacs
Golgi apparatus 2 functions
- processes & packages new lipids & proteins (processes proteins e.g. adding sugar chains/carbohydrate groups)
- makes lysosomes
What does the Golgi apparatus look like?
Like the SER but surrounded by vesicles
Looks a bit like a WiFi symbol
mitochondrion description (3 parts - including shape)
oval-shaped (sort of like a peanut)
has a double-membrane; the inner membrane has loads of folds which form cristae
the matrix is inside, which contains enzymes involved in respiration
mitochondrion function
site of aerobic respiration, where ATP is produced
chloroplast description (3 parts)
double membrane-bound flattened organelle
thylakoid membranes inside which stack to form grana - these are linked together by lamellae (long, thin thylakoid membrane)
chloroplast function
some photosynthesis happens in the grana, other parts in thick fluid called the stroma
microtubule meaning
small protein cylinders
flagellum description
two microtubules in the centre with nine pairs around the edge
flagellum function
microtubules contract to make the flagellum move to propel the cell forwards
cilium description
- have an outer membrane
- ring of nine pairs of microtubules with two in the middle (9 + 2 formation)
cilia function (+ how do they do this?)
microtubules contract to make the cilia move, which can then move substances along the cell surface
centriole description (2 parts incl. what type of cell it is found in)
tiny bundle of small, hollow protein cylinders made of microtubules
animal cells and some plant cells
centriole function
involved with separating chromosomes during cell division
capsule 2 functions
- prevents the bacteria from drying out
- covers antigens to protect it from its host’s immune system
cisterna
a closed (and flattened) sac filled with liquid, forming part of some organelles
e.g. in the Golgi apparatus, RER
Where are cisternae found?
Endoplasmic reticulums and Golgi apparatus
Describe how cells’ ultrastructures help protein production.
- Nucleolus produces ribosomes
- Ribosomes synthesise proteins/polypeptide chains
- These proteins go to the rough endoplasmic reticulum, which folds and processes them e.g. by adding sugar chains
- The proteins are transported to the Golgi apparatus by vesicles via the cytoskeleton
- They are then further processed e.g. trimming off sugar chains or adding more
- The proteins are packaged into vesicles and transported around the cell, or out of the cell through the plasma membrane where the proteins are secreted by exocytosis
cytoskeleton meaning
‘cell’ skeleton
A large network of protein fibers and other molecules that gives shape and structure to cells
microfilament meaning
thin strands of proteins
Explain the importance of the cell cytoskeleton (4).
- keeps the cell in position
- helps the transport of organelles and materials around the cell
- helps maintain the cell’s shape and stability - strengthens the cell (e.g. some organelles are bound to the cytoskeleton)
- microfilaments can allow the cell to move (e.g. a flagellum)
Explain how the nature of the cytoskeleton allows it to perform its functions.
The cytoskeleton is dynamic (constantly changing) so it can respond to changes in the cell.
Compare the way eukaryotes’ and prokaryotes’ DNA is found.
Eukaryotes: linear (has two distinct ends)
Prokaryotes: circular
Compare the organisation of eukaryotes’ and prokaryotes’ DNA.
Eukaryotes: associated with histone proteins (which DNA coils around to help give chromosomes their shape and help control genes’ activity)
Prokaryotes: proteins fold and condense DNA (through supercoiling i.e. coiling coils into a ball)
Compare the membranes of organelles of eukaryotes and prokaryotes.
Eukaryotes: membrane and non-membrane bound organlles
Prokaryotes: non-membrane bound organelles
Compare the substances that make up the cell walls of different eukaryotes and prokaryotes.
Eukaryotes: cellulose cell wall in plants, chitin cell wall in fungi, no cell walls in animals
Prokaryotes: cell wall made of a polysaccharide peptidoglycan
Do eukaryotic cells or prokaryotic cells have more organelles?
Eukaryotic cells
Compare the flagella of eukaryotes and prokaryotes (what are they made of and how are they arranged?).
Eukaryotes: when present, microtubules are arranged in the 9 + 2 formation
Prokaryotes: made of the protein flagellin, arranged in a helix
Compare the size of ribosomes in eukaryotes and prokaryotes.
Eukaryotes: bigger (>20nm, 80S)
Prokaryotes: smaller (<= 20nm, 70S)
Where do you find 70S ribosomes (more than just one)
Prokaryotic cells
Mitochondria & chloroplasts in eukaryotic cells
Compare the complexity of the cytoskeleton in eukaryotes and prokaryotes.
Eukaryotes: more complex
Prokaryotes: less complex
occular lens
eyepiece lens
diopter adjustment
next to eyepiece lens, raising or lowering the eyepiece to adjust the focus for each eye
nose piece
the circular structure where the objective lenses are screwed in
flat surface where slide is positioned
mechanical stage
thing that keeps the slide in position
stage clip
another name for the coarse/fine focus wheels
coarse/fine adjustment
How can you reposition the stage (left & right movement)?
Use the stage controls - two wheels on the lower side of the microscope
diaphragm (microscope)
Don’t think you need to know this, but it’s good to know.
Controls the amount of light that reaches the specimen
condenser (microscope)
Don’t think you need to know this, but it’s good to know.
Lens(es) below the stage that focusses light onto the specimen
Where is the diaphragm located?
Above the condenser but below the stage - although this isn’t necessarily always the case according to google images
from the bottom up, they go in alphabetical order
Types of microscopes
- Compound light microscope
- Laser scanning confocal microscope
- Scanning electron microscope
- Transmission electron microscope
Why do light microscopes have a poor resolution?
Light is used, which has a long wavelength.
Why do electron microscopes have a good resolution?
Beams of electrons are used, which have a shorter wavelength.
Where do you need to use an electron microscope and why?
In a vacuum - otherwise the electrons can be absorbed by the air
What do you need to do when preparing a TEM specimen, that you don’t have to do for a SEM specimen?
Thinly slice the specimen - the electrons aren’t being transmitted in a SEM
What do laser scanning confocal microscope images look like? What can they show?
Colourful (red, green & blue) due to flourescent dyes against a black background.
e.g. shows the cytoskeleton
What do SEM images look like?
3D coloured images of the specimen’s surface
They are ordinary black and white, but colour is added afterwards
What do TEM images look like?
2D images (that depend on the angle at which the specimen is sliced)
They are ordinary black and white, but colour can be added afterwards
How do light microscopes work? How do they form images?
A beam of light passed through the specimen. Some parts of the object absorb more light than others, producing an image.
How do laser scanning confocal microscopes work?
The specimen is tagged with fluorescent dyes.
A laser beam is passed through a lens, splitting it so that some of the light is directed to a small area on the surface of the specimen.
The laser hits the dyes, causing them to emit fluorescent light, which is focussed through a confocal aperture/pinhole (any light that isn’t focussed is rejected) onto a detector.
This is connected to a computer which generates an image. Multiple images can be combined to form 3D images of the specimen.
confocal = common focus
How do scanning electron microscopes work?
Samples are treated with a solution of heavy metals (these ions are scattered to provide contrast between structures).
A beam of electrons is sent across the specimen, knocking some of the specimen surface electrons off. These electrons that bounce off are then collected to form an image.
How do transmission electron microscopes work?
Samples are treated with a solution of heavy metals (these ions are scattered to provide contrast between structures).
Electromagnets focus a beam of electrons so that they are transmitted through the specimen to form an image. Denser parts of the specimen absorb more electrons so look darker on the image
Why might a scientist use a laser scanning electron miscroscope?
A SEM allows you to see sections of small structures that would be difficult to physically section off/cut (e.g. embryos) and creates a 3D image
Advantage of a laser scanning confocal microscope.
Can look at different depths of a specimen (3D)
Disadvantage of a laser scanning confocal microscope.
Fluorescent dyes can be toxic to the cells
Advantages of a SEM.
- Can be 3D.
- Lower resolution to transmission electron microscopes.
Disadvantage of a SEM.
Samples have to be treated with a solution of heavy metals.
Advantages of a TEM.
- High resolution so can look at small organelles e.g. ribosomes.
- Can look at internal structures of organelles in detail.
Disadvantages of a TEM.
- Samples have to be treated with a solution of heavy metals.
- Specimens need to be very thinly sliced (which can be difficult).
- Angle of slice can affect the image produced.
Compare and contrast a scanning electron microscope and a transmission electron microscope. [4 marks]
Similarities:
Both use electrons / electromagnets;
Both use vacuums / can’t image live tissue;
Both have higher magnification than optical microscopes;
Both have higher resolution than optical microscopes
Differences:
Electrons are transmitted through the specimen in TEM whereas electrons are
reflected off the surface in SEM OR TEM shows internal structure whereas SEM shows surface;
SEM can produce 3D images whereas TEM cannot;
TEM gives higher resolution than SEM;
TEM has higher maximum magnification than SEM;
SEM can be used on thicker specimens than TEM
At least one statement from similarities AND differences is required for full marks.
TEM shows ____ structure whereas SEM shows ____.
internal, surface
Name four stains.
- Iodine
- Methylene blue
- Eosin / H&E
- Giemsa
What does the H&E stain look like?
cytoplasm - pink due to the eosin
RNA/DNA e.g. in nuclei and ribosomes - purple/blue due to the haematoxylin
What does the Giemsa stain look like?
Nuclei - purple
Red blood cells can look pink
Note: cytoplasms can look pink because Giemsa stains often contain eosin (which is also in the H & E stain)
How do you prepare a microscope slide (2 types)?
- Thinly slice specimen
- Wet mount - pipette a drop of water onto middle of slide
- Pick up specimen with tweasers and place in middle of slide
- Add a drop of stain
- Place a cover slip on top, gently tilting and lowering it to prevent air bubbles
- Remove excess stain by gently dabbing with a paper towel
Why are wet mounts used?
- To prevent cells from drying out
- For liquid specimens
smear slide (+ example of use)
A wet mount where a thin layer of liquid is spread across part of the slide. Often used in blood samples
stage micrometer meaning
microscope slide “ruler” placed on the stage with units (accurate scale) used to work out the value of each division on the eyepiece graticule at a particular magnification
eyepiece graticule meaning (units?)
a “ruler” on the eyepiece with numbers but no units
1 division on a stage micrometer is equal to 0.1mm. 2 divisions on a stage micrometer is equal in length to 16 eyepiece graticule divisions (eyepiece units). What is the real length of an object that is 15 eyepiece divisions long?
1 SM division = 8 EPG divisions
1 EPG division = 0.125 SM divisions
1 SM division = 0.1mm
0.125 SM divisions = 1 EPG division = 0.0125 mm
15 EPG divisions = 0.0125 * 15 = 0.1875 mm
A plant cell was observed with an optical microscope. Describe how the length of the cell could be estimated. [2]
Measure the length of the plant cell with an eyepiece graticule (1) calibrated against a stage micrometer (1)
Describe and explain how the structure of a chloroplast is related to its function. [4 marks]
Mark in pairs, e.g. 1 and 2 - up to 4 marks for:
* Thylakoids are flattened sacs (stacked into grana, connected by lamellae);
* (Which) increase surface area for photosynthesis
- Chlorophyll / photosynthetic pigments;
- (Which) absorb light for photosynthesis
- Stroma contains enzymes;
- For photosynthesis
- (Stroma contains) DNA and ribosomes;
- For protein synthesis
- (Stroma contains) starch grains;
- For energy storage.
Describe and explain the structure and function of the cell vacuole in plant cells. [4 marks]
- Has a single membrane / a tonoplast;
- (to) maintain (internal) pressure / rigidity / prevents wilting / turgidity;
- Contains cell sap / solution of dissolved sugars / salts / amino acids;
- (Which) acts as a (temporary) food storage
OR - (Which) isolates / separates unwanted chemicals (within the cell).
How do you calculate the length of a scale bar when drawing a scientific drawing?
Scale bar image length = magnification * length you want the scale bar to represent
(and then you convert it back into mm/cm to draw it!)
How do you calculate the magnification of a photograph from a labelled scale bar?
Scale bar image length = magnification * length scale bar actually represents
Magnification = scale bar image length / length scale bar actually represents
