Cell Structure Flashcards
Function of cell surface membrane
Regulates the movement of substances into and out of the cell. Has receptor molecules allowing response to chemicals like hormones
Function of cell wall
Supports plant cells
Description of cell surface membrane
The membrane found on the surface of animal cells and just inside the cell wall of plant cells and prokaryotic cells. Its made mainly of lipids and protein
Description of cell wall
A rigid structure that surrounds plant cells. Its made mainly of the carbohydrate cellulose
Nucleus description
A large organelle surrounded by a nuclear envelope (double membrane) containing many pores. The nucleus contains chromatin (made from DNA and proteins) and a structure called the nucleolus
Function of a nucleus
It controls the cell’s activities (controlling transcription of DNA). DNA contains instructions to make proteins. The pores allow substances to move between the nucleus and cytoplasm. The nucleolus makes ribosomes
Description of a lysosome
Round organelle surrounded by a membrane, with no clear internal structure
Functions of a lysosome
Contains digestive enzymes which are kept separate from the cytoplasm by the surrounding membrane
Description of a ribosome
A very small organelle that either floats free in the cytoplasm or is attached to the rough endoplasmic reticulum. It is made from proteins not RNA and not surrounded by a membrane
Function of a ribosome
Site of protein synthesis
Description of the rough endoplasmic reticulum
A system of membranes enclosing a fluid-filled space. The surface is covered with ribosomes.
Function of rough endoplasmic reticulum
Folds and processes proteins that have been made at the ribosomes
Description of the smooth endoplasmic reticulum
A system of membranes enclosing a fluid-filled space. The surface is not covered with ribosomes.
Function of the smooth endoplasmic reticulum
Synthesizes and processes lipids
Description of a vesicle
A small fluid-filled sac in the cytoplasm, surrounded by a membrane
Function of a vesicle
Transports substances in and out of the cell and between organelles. Some are formed by the Golgi apparatus or the endoplasmic reticulum, while others are formed at the cell surface
Description of the Golgi Apparatus
A group of fluid-filled membrane-bound, flattened sacs. Vesicles are often seen at the edges of the sacs
Functions of the Golgi Apparatus
It processes and packages new lipids and proteins. It also makes new lysosomes
Description of mitochondrion
Oval shaped with double membrane. The inner one is folded forming cristae. Inside in the matrix containing enzymes for respiration
Function of a mitochondrion
The site of aerobic respiration where ATP is produced. Found in large numbers in cells that are very active and require lots of energy
Description of a chloroplast
Small, flattened structure found in plant cells. Surrounded by double membrane and has membranes inside called thylakoid membranes. These are stacked up in some parts of the chloroplast to form grana. Grana are linked together by lamellae = thin, flat pieces of thylakoid membrane.
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)
Description of a centriole
Small, hollow cylinders, made of microtubules (tiny protein cylinders). Found in animal cells, but only some plant cells
Function of a centriole
Involved in the separation of chromosomes during cell division
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. Known as the 9+2 formation
Function of cilia
The microtubules allow cilia to move used by the cell to move substances along the cell surface
Description of Flagellum
Like cilia but longer as they stick out from the cell surface and surrounded by the plasma membrane. Inside like cilia there is a 9+2 formation of microtubules
Stages of how organelles are involved in protein production
1) Proteins are made at the ribosomes
2) The ribosomes on RER make proteins that are excreted or attached to the cell membrane. The free ribosomes in the cytoplasm make proteins that stay
3) New proteins produced at the RER are folded and processed (eg sugar chains are added) in the RER
4) They are transported in vesicles from the ER to the Golgi apparatus
5) At the Golgi apparatus, the proteins may undergo further processing (eg sugar chains are trimmed or more are added)
6) The proteins enter more vesicles to be transported around the cell
What is the cytoskeleton
Network of protein threads arranged as microfilaments and microtubules
Four main functions of the cytoskeleton
- Support the cell’s organelles keeping them in position
- Strengthen the cell maintaining shape
- Responsible for the movement of materials within the cell e.g. chromosomes in cell division
- The proteins can cause movement such as cilia and flagella
Features of a prokaryotic cell
- Extremely small
- DNA is circular
- No nucleus
- Cell wall made of a polysaccharide
- Few and no membrane bound organelles
- Flagella made from flagellin in a helix
- Small ribosomes
Features of a eukaryotic cell
- Larger cell
- DNA is linear
- Nucleus present
- No cell wall (animals), cell wall made from cellulose (plants) or chitin (fungi)
- Many organelles
- Flagella made of microtubule proteins arranged in 9+2 formation
Example of a prokaryote
E. coli (bacterium)
Example of a eukaryote
Human liver cell
What is it like to look at a prokaryote under a microscope
Cannot see their internal structures under a normal microscope (need electron)
Magnification =
Image size / object size
Four types of microscopes
Light, Laser Scanning confocal, Transmission Electron, Scanning Electron
Features of a light microscope
- Use light
- Lower resolution (0.2 micrometers)
- Maximum useful magnification is around x 1500
Features of a laser scanning confocal
- Use intense beams of light (lasers)
- Specimen is tagged in dye causing it to give off light which produces a 3D image
- Pinhole means any out of focus light is blocked to give a clearer image
- Can look at objects at different depths in thick specimens
Features of transmission electron microscopes
- Use electromagnets to focus a beam of electrons that is transmitted through the specimen
- Denser parts absorb more electrons and therefore look darker
- Produces as high resolution image to look at range of organelles
Features of scanning electron microscopes
- A beam of electrons is scanned across the specimen knocking off electrons form the specimen
- These gather in the cathode ray tube forming an image
- Show the surface and can be 3D but lower resolution than TEM’s
Light microscope maximum resolution
0.2 micrometers
TEM maximum resolution
0.0002 micrometers
SEM maximum resolution
0.002 micrometers
TEM maximum magnification
Can be more than x 1 000 000
SEM maximum magnification
Usually less than x 500 000
Light microscope maximum magnification
x 1500
Why do you stain samples
To allows you to see certain organelles more clearly - light will show up clear if no organelles present
What would you use to stain cell cytoplasm’s
Eosin
What would you use to stain DNA
Methylene blue
How would you stain for an electron microscope
Objects are dipped in a heavy solution of metals and the metal ions scatter the electrons creating a contrast as some parts show up darker than others
How to prepare a dry mount slide
- Take a thin slice of the specimen
- Use tweezers to pick up the specimen and place on the middle of the clean slide
- Place a cover slip on top
How to prepare a wet mount slide
- Pipette a small drop of water onto the slide
- Using tweezers place the specimen on top
- Lower cover slip avoiding air bubbles
- Add a drop of stain to the edge of the cover slip and a paper towel at the other end.
How to use a light microscope
- Clip the slide with specimen onto the stage
- Select lowest-powered objective lens
- Use coarse adjustment know bringing the stage up to the objective lens
- Look down eyepiece and adjust with coarse and fine adjustment knob till clear
- Can swap to larger magnification
What is an eyepiece graticule
Fitted onto the eyepiece like a transparent ruler with numbers but no units
What is a stage micrometer
Placed on the stage and is a microscope slide with an accurate scale used to work out the value of the divisions of the eyepiece graticule at a magnification
