Cell Structure Flashcards
What is the description of a cell membrane?
The membrane found on the surface of animal cells and just inside the cell wall of plant cells and prokaryotic cells. It’s made mainly of lipids and protein.
What is the function of a cell membrane?
Regulates the movement of substances into and out of the cell. It also has receptor molecules on it, which allow it to respond to chemicals like hormones.
Whats the description of a cell wall?
A rigid structure that surrounds
plant cells. It’s made mainly of
the carbohydrate cellulose.
What is the function of a cell wall?
Supports plant cells.
Whats the description of a nucleus?
A large organelle surrounded by a nuclear envelope (double membrane), which contains many pores. The nucleus contains chromatin (which is made from DNA and proteins) and a structure called the nucleolus.
Whats the function of a nucleus?
The nucleus controls the cell’s activities (by controlling the transcription of DNA. DNA contains instructions to make proteins The pores allow substances (e.g. RNA) to move between the nucleus and the cytoplasm. The nucleolus makes ribosomes
Whats the description of a lyosome?
A round organelle surrounded
by a membrane, with no clear
internal structure.
What is the function of a lyosome?
Contains digestive enzymes. These are kept separate from the cytoplasm by the surrounding membrane, and can be used to digest invading cells or to break down worn out components of the cell
Whats the description of a ribosome?
A very small organelle that either floats free in the cytoplasm or is attached to the rough endoplasmic reticulum. It’s made up of proteins and RNA. It’s not surrounded by a membrane.
Whats the function of a ribosome?
The site where proteins
are made.
Whats the description of Rough endoplasmic reticulum?
A system of membranes enclosing
a fluid-filled space. The surface is
covered with ribosomes.
Whats the function of the rer?
Folds and processes proteins
that have been made at the
ribosomes.
Whats the description of ser?
Similar to rough endoplasmic
reticulum, but with no ribosomes.
What is the function of ser?
Synthesises and
processes lipids.
What is the description of a vesical?
A small fluid-filled sac in
the cytoplasm, surrounded
by a membrane.
What is the function of a vesical?
Transports substances in and out of the cell (via the plasma membrane) and between organelles. Some are formed by the Golgi apparatus or the endoplasmic reticulum, while others are formed at the cell surface.
Whats the description of a golgi?
A group of fluid-filled,
membrane-bound, flattened sacs.
Vesicles are often seen at the
edges of the sacs.
What is the function of a golgi?
It processes and packages
new lipids and proteins.
It also makes lysosomes
Whats the description of a mitochondrion?
They’re usually oval-shaped. They have a double membrane — the inner one is folded to form structures called cristae. Inside is the matrix, which contains enzymes involved in respiration.
Whats the function of a mitocondrion?
The site of aerobic respiration, where ATP is produced. They’re found in large numbers in cells that are very active and require a lot of energy.
Whats the description of a chloroplast?
A small, flattened structure found in plant cells. It’s surrounded by a double membrane, and also has membranes inside called thylakoid membranes. These membranes are stacked up in some parts of the chloroplast to form grana. Grana are linked together by lamellae — thin, flat pieces of thylakoid membrane.
Whats the function of a chloroplast?
The site where photosynthesis takes place. Some parts of photosynthesis happen in the grana, and other parts happen in the stroma (a thick fluid found in chloroplasts).
Whats the description of a centriole?
Small, hollow cylinders, made of microtubules (tiny protein cylinders). Found in animal cells, but only some plant cells.
What is the function of a centriole?
Involved with the separation
of chromosomes during cell
division
Whats the description of cilia?
Small, hair-like structures found on the surface membrane of some animal cells. In cross- section, they have an outer membrane and a ring of nine pairs of protein microtubules inside, with two microtubules in the middle.
What is the function of cilia?
The microtubules allow the cilia
to move. This movement is used
by the cell to move substances
along the cell surface.
Whats the description of flagella?
Flagella on eukaryotic cells are like cilia but longer. They stick out from the cell surface and are surrounded by the plasma membrane. Inside they’re like cilia too — two microtubules in the centre and nine pairs around the edge.
Whats the function of flagella?
The microtubules contract to make the flagellum move. Flagella are used like outboard motors to propel cells forward (e.g. when a sperm cell swims).
How is protein produced in a cell?
1) Proteins are made at the ribosomes.
2) The ribosomes on the rough endoplasmic
reticulum (ER) make proteins that are
excreted or attached to the cell membrane.
The free ribosomes in the cytoplasm make
proteins that stay in the cytoplasm.
3) New proteins produced at the rough ER
are folded and processed (e.g. sugar chains
are added) in the rough ER.
4) Then they’re transported from the
ER to the Golgi apparatus in vesicles.
5) At the Golgi apparatus, the proteins may
undergo further processing (e.g. sugar
chains are trimmed or more are added).
6) The proteins enter more vesicles to be
transported around the cell.
E.g. glycoproteins (found in mucus) move
to the cell surface and are secreted.
Whats the cytoskeleton?
1) The organelles in cells are surrounded by the cytoplasm. The cytoplasm is more than just
a solution of chemicals though — it’s got a network of protein threads running through it.
These protein threads are called the cytoskeleton.
2) In eukaryotic cells the protein threads are arranged as microfilaments (small solid strands)
and microtubules (tiny protein cylinders).
What are 4 functions of the cytoskeleton
The cytoskeleton has four main functions:
1) The microtubules and microfilaments support the
cell’s organelles, keeping them in position.
2) They also help to strengthen the cell and maintain its shape.
3) As well as this, they’re responsible for the movement of materials
within the cell. For example, the movement of chromosomes
when they separate during cell division depends on contraction
of microtubules in the spindle
4) The proteins of the cytoskeleton can also cause the cell to move.
For example, the movement of cilia and flagella is caused by
the cytoskeletal protein filaments that run through them. So in
the case of single cells that have a flagellum (e.g. sperm cells),
the cytoskeleton propels the whole cell.
The cytoskeleton is dynamic (constantly changing), which allows it
to respond to changes in the cell and carry out its functions.
Whats the difference between prokaryotes and eukaryotes?
PROKARYOTES
Extremely small cells (less than 2 µm diameter)
DNA is circular
No nucleus — DNA free in cytoplasm
Cell wall made of a polysaccharide, but not cellulose or chitin
Few organelles and no membrane-bound organelles, e.g. no mitochondria
Flagella (when present) made of the protein flagellin, arranged in a helix
Small ribosomes
EUKARYOTES
Larger cells (about 10-100 µm diameter)
DNA is linear
Nucleus present — DNA is inside nucleus
No cell wall (in animals), cellulose cell wall (in plants) or chitin cell wall (in fungi)
Many organelles — mitochondria and other membrane-bound organelles present
Flagella (when present) made of microtubule
proteins arranged in a ‘9 + 2’ formation
Larger ribosomes
What is magnification?
Magnification is how much bigger the image is than the specimen
(the sample you’re looking at).
What is resolution?
Resolution is how detailed the image is. More specifically, it’s how well a microscope
distinguishes between two points that are close together. If a microscope lens can’t
separate two objects, then increasing the magnification won’t help.
How to work out magnification
magnification = image size/object size
Whats a light microscope?
1) Light microscopes use light
2) They have a lower resolution than electron microscopes — they have a maximum resolution
of about 0.2 micrometres (µm). So they’re usually used to look at whole cells or tissues.
3) The maximum useful magnification of a light microscope is about × 1500.
Whats a laser scanning confocal microscope?
1) Laser Scanning Confocal Microscopes use laser beams (intense beams of
light) to scan a specimen, which is usually tagged with a fluorescent dye.
2) The laser causes the dye to fluoresce — give off light. This light is then
focused through a pinhole onto a detector. The detector is hooked up
to a computer, which generates an image. The image can be 3D.
3) The pinhole means that any out-of-focus light is blocked,
so these microscopes produce a much clearer image
than a normal light microscope.
4) They can be used to look at objects at different depths in thick specimens.
Whats a electron microscope?
Electron microscopes use electrons instead of light to form an image.
They have a higher resolution than light microscopes so give more detailed
images. There are two kinds of electron microscope:
What is a transmission electron microscope?
Transmission electron microscope (TEM) — use electromagnets to focus
a beam of electrons, which is then transmitted through the specimen.
Denser parts of the specimen absorb more electrons, which makes them
look darker on the image you end up with. TEMs are good because
they provide high resolution images (so they can be used to look at a
range of organelles) but they can only be used on thin specimens.
A TEM image of a mitochondrion is shown above on the right.
Whats a scanning electron microscope?
Scanning electron microscope (SEM) — scan a beam of electrons across
the specimen. This knocks off electrons from the specimen, which are
gathered in a cathode ray tube to form an image. The images produced
show the surface of the specimen and can be 3D. But they give lower
resolution images than TEMs. Here’s an SEM image of a mitochondrion.
comparison light microscope TEM SEM
light microscope maximum resolution 0.2 µm maximum magnification × 1500 TEM maximum resolution 0.0002 µm maximum magnification can be more than × 1 000 000 SEM maximum resolution 0.002 µm maximum magnification usually less than × 500 000
Why do we need to use stain?
In light microscopes and TEMs, the beam of light (or electrons) passes through the object being viewed.
An image is produced because some parts of the object absorb more light (or electrons) than others.
2) Sometimes the object being viewed is completely transparent. This makes the whole thing look white
because the light rays (or electrons) just pass straight through.
3) To get round this, the object can be stained:
How to stain in light microscope?
Staining samples for light microscopes:
• For the light microscope, this means using
some kind of dye. Common stains include
methylene blue and eosin.
• The stain is taken up by some parts of the
object more than others — the contrast
makes the different parts show up.
• Different stains are used to make different things
show up. For example, eosin is used to stain cell
cytoplasms. Methylene blue stains DNA.
• More than one stain can be used at once.
How to stain e- microscope?
Staining samples for electron microscopes:
For the electron microscope, objects are dipped in a solution of heavy
metals (like lead). The metal ions scatter the electrons, again creating
contrast — some parts of the object show up darker than others.
Electron micrograph images are always
black and white even when stained,
but colour can be added artificially
after the image has been made.
How to prepare a microscope slide dry mount?
Dry mount
Your specimen needs to let light through it for you to be able to
see it clearly under the microscope. So if you’ve got quite a thick
specimen, you’ll need to take a thin slice to use on your slide.
• Use tweezers to pick up your specimen and
put it in the middle of a clean slide.
• Pop a cover slip (a square of thin, transparent plastic or glass) on top
How to prepare a microscope slide wet mount?
Wet mount
• Start by pipetting a small drop of water onto the slide.
Then use tweezers to place your specimen on top of the water drop.
• To put the cover slip on, stand the slip upright on the slide, next to the water
droplet. Then carefully tilt and lower it so it covers the specimen. Try not to
get any air bubbles under there — they’ll obstruct your view of the specimen.
• Once the cover slip is in position, you can add a stain. Put a drop of stain next
to one edge of the cover slip. Then put a bit of paper towel next to the opposite
edge. The stain will get drawn under the slip, across the specimen.
Here’s How to Use a Light Microscope…
1) Start by clipping the slide containing the specimen
you want to look at onto the stage.
2) Select the lowest-powered objective lens
(i.e. the one that produces the lowest magnification).
3) Use the coarse adjustment knob to bring the stage up to just
below the objective lens.
4) Look down the eyepiece (which contains the ocular lens).
Use the coarse adjustment knob to move the stage downwards,
away from the objective lens until the image is roughly in focus.
5) Adjust the focus with the fine adjustment knob, until
you get a clear image of what’s on the slide.
6) If you need to see the slide with greater magnification,
swap to a higher-powered objective lens and refocus.
What is a Eyepiece Graticule and Stage Micrometer
Eyepiece Graticule and Stage Micrometer
1) Sometimes, you might want to know the size of your specimen.
And that’s where the eyepiece graticule and stage micrometer come in — they’re a bit like rulers.
2) An eyepiece graticule is fitted onto the eyepiece. It’s like a transparent ruler with numbers, but no units.
3) The stage micrometer is placed on the stage — it is a microscope slide with an accurate scale (it has units)
and it’s used to work out the value of the divisions on the eyepiece graticule at a particular magnification.
4) This means that when you take the stage micrometer away and replace it with the slide containing your
specimen, you’ll be able to measure the size of the specimen.
How to use a Eyepiece Graticule and Stage Micrometer?
Line up the eyepiece graticule and the stage micrometer.
2) Each division on the stage micrometer is 0.1 mm long.
3) At this magnification,1 division on the stage micrometer
is the same as 4.5 divisions on the eyepiece graticule.
4) To work out the size of 1 division on the eyepiece
graticule, you need to divide 0.1 by 4.5:
1 division on eyepiece graticule = 0.1 ÷ 4.5 = 0.022 mm
5) So if you look at an object under the microscope at
this magnification and it’s 20 eyepiece divisions long,
you know it measures: 20 × 0.022 = 0.44 mm
Remember: at a different magnification, 1 division on the stage micrometer
will be equal to a different number of divisions on the eyepiece graticule —
so the eyepiece graticule will need to be re-calibrated
Eyepiece graticule
