Cell Structure Flashcards
1
Q
What is a eukaryotic cell?
A
- the more complex of the two
- contain a number of different organelles
2
Q
ORGANELLE - cell-surface membrane
A
- a bilayer of phospholipids with proteins embedded it
- receptors and antigens are attached to this surface
- controls the entry and exit of substance in and out of the cell
3
Q
ORGANELLE - nucleus
A
- an organelle containing chromosomes, which consist of protein-bound, linear DNA
- contains one or more nucleoli
- has a double membrane called a nuclear envelope - this has pores to allow mRNA to leave the nucleus
4
Q
ORGANELLE - nucleolus
A
- found in the nucleus
- may be one or more present
- make ribosomes
5
Q
ORGANELLE - mitochondria
A
- has a double membrane
- the inside of this double membrane is folded into structure called cristae
- matrix fills the inside of the mitochondria
- contains their own small ribosomes and their own DNA
- site of aerobic respiration
6
Q
ORGANELLE - chloroplasts
A
- found in plant and algae cells
- site of the reactions of photosynthesis
- also have a double membrane
- on the inside, there are thylakoid membranes - these are arranged in stacks called grana which are linked by lamellae
- contain their own small ribosomes and circular DNA
7
Q
ORGANELLE - Golgi apparatus/Golgi body
A
- consists of a series of fluid filled flattened sacs made of membrane
- process proteins and lipids and package them into vesicles which are transported out of and around the cell
- often seen at the edge of sacs
8
Q
ORGANELLE - lysosomes
A
- a type of vesicle that contains lysozyme enzymes
- these enzymes digest engulfed material or worn out organelles
9
Q
ORGANELLE - ribosomes
A
- translate mRNA to synthesise proteins
- made of two subunits of protein as well as RNA
- found attached to the rough endoplasmic reticulum or free in the cytoplasm
- don’t have a membrane
10
Q
ORGANELLE - rough endoplasmic reticulum
A
- can be called RER (must call it by full name at least once in answer to get marks however)
- a series of fluid filled flattened sacs of membrane
- has ribosomes attached - this is where it gets its rough appearance
- the proteins synthesised by the ribosomes are folded and processed here
11
Q
ORGANELLE - smooth endoplasmic reticulum
A
- can be called SER (must call it by full name at least once in answer to get marks however)
- similar to the rough endoplasmic reticulum
- just has no ribosomes attached
- synthesises and processes lipids
12
Q
ORGANELLE - vacuole
A
- a large organelle surrounded by a membrane that contains sap
- has a role in providing turgidity in plant cells by maintaining pressure inside the cell so the plant does not wilt.
13
Q
ORGANELLE - cell wall
A
- made from cellulose in plants and algae cells
- made from chitin in fungal cells
- provides support and structure to the cell
- in plants, there are small channels through the cell walls which connect the cells - these are called plasmodesmata
14
Q
Cell specialisation
A
In complex multicellular organisms, eukaryotic cells (the stem cells) become specialised for specific functions
15
Q
What is a tissue?
A
A group of specialised cells working together to perform a particular function.
16
Q
What is an organ?
A
A group of tissues working together to perform a particular function.
17
Q
What is an organ system?
A
Organs working together form an organ system.
18
Q
Rank cell organisation
A
- unspecialised cell/stem cell
- specialised cell (e.g. muscle cell, nerve cells, gametes)
- tissue
- organ (e.g. lungs)
- organ system (e.g. respiratory system)
19
Q
What are prokaryotic cells?
A
- much smaller than eukaryotic cells
- also differ from eukaryotic cells in having no nucleus
- prokaryote literally means ‘before nucleus’
20
Q
How are ribosomes different in prokaryotic cells vs eukaryotic cells?
A
They are smaller in prokaryotic cells.
21
Q
Prokaryotic cells - cell wall
A
- supports the cell
- made of murein (a glycoprotein)
22
Q
Prokaryotic cells - plasmids
A
- small loops of DNA
- contain genes for characteristics such as antibiotic resistance
23
Q
Prokaryotic cells - slime capsule
A
- THEY MAY HAVE IT
- surrounds the cell
- gives it protection
24
Q
Prokaryotic cell - flagella
A
- THEY MAY HAVE IT
- can have one or more
- for movement
25
Prokaryotic cells - list of organelles
- cell wall
- cell membrane
- flagellum
- plasmid
- circular DNA
- ribosomes
- slime capsule
26
What are microscopes?
Instruments that produce a magnified image of an object.
27
What is the material you put under a microscope called?
Specimen or object.
28
What do you call the area that can be observed with a microscope?
The field of view.
29
What do you call the appearance of the object under the microscope?
The image.
30
Go and label a microscope
31
How do you use a microscope (the method)?
1. Prepare a temporary mount (basically a temporary slide) or use a prepared slide.
2. Place this on stage.
3. Start on the lowest magnification.
4. Use the coarse focus to bring the image into view.
5. Adjust using fine focus.
6. If you want to view at a higher magnification, turn the nosepiece to the next objective lens.
32
What is the equation to calculate the total magnification of a microscope?
Ocular lens x eyepiece lens = total magnification
33
Define magnification
Describes how much larger it appears compared to the actual size of the object.
Increases size of image but doesn’t necessarily show more detail, which is where resolution comes in.
34
What is the maximum magnification of an optical microscope?
x1500
35
Define resolution
The smallest distance apart that two objects can be and still appear as separate items.
Determined by wavelength of light.
36
What is the maximum resolution of an optical microscope?
0.2 micrometers
37
What is an artefact?
Things that appear a the microscope image but are not supposed to be there.
A results from the way the specimen is prepared.
38
Electron microscope (in general)
- use a beam of electrons (instead of light), which can be focused in electromagnets
- **Magnification** - x1500000
- **Resolution** - 0.0002 micrometers
- they can view small organelles such as ribosomes, endoplasmic reticulum and greater detail of the mitochondria (you can’t see this on an optical microscope)
- HOWEVER, because electrons are easily absorbed or deflected by molecules in the air, a near **vacuum** has to be created within an electronic microscope so that it works effectively
- therefore we cannot study living specimens with an electron microscope
- only produce black and white images
39
TYPES OF ELECTRON MICROSCOPE- transmission electron microscopes (TEM)
- **How it works** - electrons pass through the specimen and the dense parts absorb more electrons so appear darker
- have a typical maximum **magnification** of x1000000
- high **resolution** - up to 0.2nm
- produces high resolution images of the internal structure of organelles
- HOWEVER they require very thin specimens, which can be difficult to prepare
40
TYPES OF ELECTRON MICROSCOPES - scanning electron microscopes (SEM)
- **How it works** - a beam of electrons scans the specimen, which produces a 3D image of the external structure of the specimen
- **Max resolution** - typically 2nm
- **Max magnification** - x100000
41
What precautions must be taken before cell fractionation?
The solution that the tissue is put in must be…
- **Cold** - to reduce enzyme activity that could damage organelles
- **Buffer solution should be added** - so extremes/fluctuations of pH don’t denature the enzymes or proteins
- **Same water potential** - the fluid must have the same WP as the cells in the tissues so there is no osmosis and organelles don’t shrivel or burst.
- **Isotonic** - tissue and solution should have the same concentration of chemical - goes back to water potential.
42
THE PROCESS - cell fractionation
1. **Homogenisation** - cells are broken up by the homogeniser (or blender). This disrupts the cell membrane, so the cell is broken open and releases the organelles from the cell.
2. **Filtration** - the homogenised cell solution is filtered through a gauze to separate any large cell debris or complete cells. The much smaller organelle pass straight through.
3. **Ultracentrifugation** - the process by which the fragments in the filtered homogenate are separated in a machine called a centrifuge, which spins tubes of homogenate at very high speeds in order to create a centrifugal force.
- The tube of filtrate is placed in centrifuge and spun at a slow speed, so the heaviest organelles, like the nuclei, are flung to the bottom. The forms a thin sediment known as the pellet.
- The supernatant (the fluid at the top of the tube) is removed, leaving just the pellet.
- The supernatant is transferred to another tube and spun in the centrifuge at a faster speed than before, so the next heaviest organelles, the mitochondria, a forced to the bottom of the tube.
- This process is continues until all wanted organelles are separated.
43
Cell organelles from heaviest to lightest?
- nuclei
- chloroplasts
- mitochondria and lysosomes
- fragments of plasma membrane and endoplasmic reticulum
- ribosomes
44
How to prepare a slide
1. Pipettes a drop of water onto the slide.
2. Place a specimen on with tweezers and stain (iodine for plants, methylene blue for animals or heavy metals for SEM).
3. Then stand the cover slip next to it and lower it on top of the specimen.
