Chapter 2 - Cell structures + microscopy Flashcards
Describe the structure of the nucleus
Nuclear envelope which has nuclear pores. Also has a nucleolus made of RNA.
Describe the function of the nucleus
- Cell’s control centre.
- DNA replication.
- Transcription and RNA processing.
- Ribosomes and RNA leave through nuclear pores
Describe the structure of the nuclear envelope
- Has protein lined channels called nuclear pores.
- Has a double membrane
Describe the function of the nuclear envelope
Nuclear pores facilitate the movement of materials in and out of the nucleus
Describe the structure of the nucleolus
- Not membrane bound
- Contains DNA
- Chromatin is the genetic material
- DNA is wound around histones
Describe the function of the nucleolus
- Makes ribosomes
- Site of tRNA production
When cell is not dividing: Chromatin is extended
When cell about to divide: Chromatin coils tightly into chromosomes
Describe the structure of the mitochondria
- Contains an enzyme rich liquid called the matrix
- Surrounded by a double membrane in which the inner membrane is fold to form cristae - this provide a large surface area.
- Contain their own DNA (mtDNA) and ribosomes
Describe the function of the mitochondria
Site of aerobic respiration
Produces ATP
Found in muscle + epithelial cells
Describe the structure of the golgi apperatus
- Contain fluid-filled sacs known as cisternae
- Contain smaller vesicles which are hollow
Describe the function of the golgi apperatus
- Process and package lipids and proteins - done by cisternae
- Store and transport lipids and proteins - done by the vesicles
- Synthesise lysosomes (specialised vesicles)
Describe the structure of the Rough ER
- Has folded membranes called cisternae, which enclose a fluid filled space
- Has ribosomes on the outer surface area
- Large surface area
Describe the function of the Rough ER
- Synthesis of proteins
- Provided a pathway for materials, such as proteins to be transported around the cell (into cisternae and to the Golgi)
Describe the structure of the Smooth ER
- Contains a network of membranes called cisternae
- Large surface area
Describe the function of the Smooth ER
Synthesise, store and transport lipids and carbohydrates
Describe the structure of Ribosomes
- Made up of proteins and rRNA
- Consists of one large and one small unit
- Not surrounded by a membrane
- Some in cytoplasm, some bound to rough ER
Describe the function of Ribosomes
- Site of protein synthesis
- Involved in translation - translate genetic material into proteins
- Eukaryotic cells contain 80S ribosomes, whereas prokaryotic contain 70S ribosomes
Describe the structure of the plasma membrane
- Found on the surface of animal cells
- Mainly made up of lipids and proteins
Describe the function of the plasma membrane
1.Controls movement of substances in and out of cell - its partially permeable
2. Cell signalling - receptors can detect signals from other cells
Describe the structure of the cell wall
- Made of cellulose
- Contains channels (gaps) called plasmodesmata
Describe the structure of the cell wall
- Supports the cell - contents of the cell press against it to make it rigid
- Prevents the cell from bursting - cell can withstand high osmotic pressure
- Allows exchange of substances between cells because the plasmodesmata connects neighbouring cells
Describe the structure of chloroplasts
- Contain fluid-filled sacs called thylakoids which are stacked up to form grana
- Surrounded by a double membrane, enclosing a fluid known as storm (like the cytoplasm)
- Contain their own DNA and ribosomes
Describe the function of chloroplasts
Site of photosynthesis - these reactions take place in the grana and stroma
Describe the structure of the vacuole
- Contains cell sap (solution of sugar and salts)
- Surrounded by a selectively permeable membrane known as tonoplast
Describe the function of the vacuole
- Helps to maintain pressure within the cell - keeps the cell rigid and stops the plant from wilting
Describe the structure of lysosomes
- Surrounded by a membrane to keep enzymes separate from the cytoplasm of the cell
- Contain hydrolytic enzymes (eg; proteases)
Describe the function of lysosomes
1 Digests invading cells - this process uses enzymes
2. Break down waste material - including old organelles
Describe the structure of centrioles
- Small tubes of proteins.
2.There is a pair of them next to the nucleus in animal cells and in the cells of some Protoctista. You don’t find them in flowering plants and most fungi - Made of microtubules
Describe the function of centrioles
- Take part in cell division - they form the spindle fibres which move chromosomes during nuclear division
- Form cilia and flagella
Describe the structure of flagella and cilia
- Running through centre of both are 9 pairs of microtubules arranged in a circle, with another pair in the centre.
- They use ATP to move relative to the pairs next to them. This creates a bending motion.
Describe the function of flagella and cilia
Cilia - essential for the locomotion of specific organisms (e.g: wafting mucus). Found in trachea and fallopian tube
Flagella - whip like organelle (found on sperm). They move the cell
What is the cytoskeleton?
The cytoskeleton is present throughout the cytoplasm and provides structure and support to the cell. It consists of 3 main components: microfilaments, microtubules, and intermediate filaments.
What are microtubules?
- Made of the protein actin.
- Involved in cell movement and locomotion, such as crawling and muscle contraction
What are microtubules?
- Made of the protein tubulin.
- Form a scaffold-like structure throughout the cell.
- Form the main component of the mitotic spindle, used for cell division.
- Act as tracks for intracellular transport of vesicles and organelles.
What are intermediate filaments?
- Maintain the position of organelles within the cell.
- Responsible for the mechanical strength of certain tissues, such as the skin and hair.
Describe algal cells
1.Contain the same organelles as plant cells.
2. Contain chloroplasts with different shapes to those found in plant cells.
Describe fungal cells:
1.Contain most of the organelles found in plant cells.
2. Do not contain chloroplasts.
3. Contain cell walls made up of chitin rather than cellulose.
What is the cytoskeleton?
Made up of protein filaments - form a network.
Present in cytoplasm. Provides structure and support to cell.
Has 3 main component: microfilaments, microtubules, intermediate filaments
What are microfilaments made from?
The protein actin
What is the function of microfilaments?
Involved in cell movement and cell contraction during cytokinesis + locomotion eg: crawling and muscle contraction.
What are microtubules made from?
the protein tubulin
What is the function of microtubules?
Form a scaffold-like structure throughout the cell, which determines the shape of cell
Form the main component of spindle fibers
Act as tracks for intracellular transport of vesicles and organelles
What is the function of intermediate filaments?
Maintain the position of organelles within the cell
Responsible for the mechanical strength of certain tissues, such as skin and hair.
What is the difference between magnification and resolution?
Magnification is how many times larger an image is than the object.
But resolution is the ability to distinguish between two separate points (or how detailed the image is).
How do you calculate magnification?
magnification = image size/ actual size
What does it mean to a calibrate the microscope ?
Finding out what one graticule division is.
What is used to calibrate the eyepiece graticule?
A stage micrometer is used to calibrate the eyepiece graticule.
What are the steps to calibrate the eyepiece graticule?
- Place the stage micrometer on the microscope stage and focus on the scale using the lowest magnification.
- Align the zero mark of the eyepiece graticule with the zero mark of the stage micrometer.
- Count the number of graticule divisions that fit into one micrometer division.
- Use the formula to calculate the size of each graticule division at that magnification
What is the formula to calculate the size of each graticule division at that magnification:
graticule division = size of one micrometer division/number of
graticule divisions
How do light microscopes work?
???
State the max.resolution of a light microscope
Around 200 nm / 0.2 μm
State the max. magnification of a light microscope
1500x
What are the 4 ways a sample could be a prepared?
- wet mount
- dry mount
- squash slides
- smear slides
Describe how to prepare a wet mount
- Use a pipette to place a small drop of water onto the centre of the glass slide.
- Use a pair of forceps to place a thin section of the specimen onto the drop of water. The specimen should be thin enough to allow light to pass through.
- Add a few drops of stain (e.g. iodine in potassium iodide) to the specimen. This increases contrast and allows cell components to become visible.
- Slowly add a cover slip (a clear glass square) onto the specimen.
What are some examples of specimens that could need a wet mount?
Aquatic organisms + other living organisms
Describe how to prepare a dry mount
Solid specimens are viewed whole, or cut into very thing slices with a sharp blade. (That’s called sectioning)
Then the specimen is placed directly onto the slide and covered with a cover slip.
What are some examples of specimens that could need a dry mount?
Hair, pollen, dust and insect parts can be viewed whole
Muscle tissue or plants can be sectioned and viewed this way.
Describe how to prepare squash slides
A wet mount is first prepared and the cover slip is pressed to squash the cells.
What are some examples of specimens that could need squash slides?
Soft samples eg: root tip squashes
Describe how to prepare smear slides
The edge of a slide is used to smear the sample to create a thin, even coating on a separate slide.
A cover slip is then placed over the sample
What are some examples of specimens that could need smear slides?
Cells in the blood
What are the steps for viewing a microscope slide?
- Clip the prepared microscope slide onto the stage.
2.Select the objective lens with the lowest power.
3.Use the coarse focus to bring the stage just below the objective lens. - Look down the eyepiece and use the coarse focus to move the stage downwards until the image is roughly in focus.
5.Use the fine focus to make the image clearer. - If a higher magnification is needed, swap to a more powerful objective lens and refocus.
How do you draw a cell in the exam?
- Include a title
- State the magnification or scale
- Be drawn with a sharp pencil
- Include smooth, continuous lines
- Include labels
- Include accurate sizes of observable structures
How do electron microscopes work?
A beam of electrons with a wavelength of less than 1nm is used to illuminate the specimen.
Why can more detail be seen in electron microscopes than light microscopes?
Because electrons have much smaller wavelength than light waves
What are the two different types of electron microscopes?
TEM -Transmission electron microscopes
SEM -Scanning electron microscopes
How do TEMs work?
Transmission electron microscopes (TEMs) use electromagnets to transmit a beam of electrons through a specimen. The denser parts absorb more electrons, so appear darker in the image formed.
What are two disadvantages of TEMs?
The specimen must be viewed in a vacuum, meaning only non-living or dead organisms can be observed.
The specimen must be thin to allow electrons to pass through.
The image doesn’t have colour
What is an advantage of TEMs?
TEMs have a better resolution than both light microscopes and SEMs
What is the resolution of TEMs?
Maximum of around 0.5 nm
What is the magnification of TEMs?
Maximum of around x 1,500,000
How do SEMs work?
Scanning electron microscopes (SEMs) scan a beam of electrons across the surface of a specimen. Reflected electrons are then used to form an image.
What are two advantages of SEMs?
SEMs produce 3D images of the surface of the specimen.
SEMs can be used on thicker specimens than TEMs (it doesn’t have to be as thin)
What are two disadvantages of SEMs?
Like TEMs, SEMs can only view non-living or dead specimens.
The image doesn’t have colour
What is the resolution of SEMs and is it better than TEMs
Maximum of around 5 nm.
No, it has a worse resolution than TEMs
What is the magnification of SEMs?
Maximum of around x 1,500,000.
How do Laser scanning confocal microscopes work?
- They use a laser beam (a single spot of focused light) to scan a specimen that has been tagged with a fluorescent dye.
- The dyed components give off light which is focused through a pinhole and onto a detector. This detector is connected to a computer which generates an image.
- This image can then be converted into a 3D image.
What is an advantage of laser scanning confocal microscopes?
The pinhole blocks any out-of-focus light so the microscope can produce clearer images than a light microscope.
What is a disadvantage of laser scanning confocal microscopes?
They have a lower resolution than electron microscopes.
What can laser scanning confocal microscopes be used for?
Look at different depths within a specimen.
Observe living specimens.
