Biology OCR A A-LEVEL ; Cell structure

What are the three types of microscopes?

Optical Microscopes, Laser-scanning microscopes and electron microscopes

What are the advantages of a light microscope.

They are

1. Portable

2. Relatively cheap

3. Easy to use

4. You can view live organisms

What are the disadvantages of a light microscope?

Organelles such as ribosomes cannot be distinguished.

What is a laser-scanning microscope?

a microscope that uses a laser to scan an object point by point to assemble a pixilated image

Does a laser-scanning microscope have high or low resolution?

Relatively high

Does a laser scanning microscope have high or low contrast?

High contrast

What other features does a laser scanning microscope have?

Depth selectivity

What is depth selectivity?

Viewing internal structures at different depths

What is the advantage of depth selectivity?

- You can view organelles within a specimen

- You can view the internal structure of a specimen

Examples of uses of laser-scanning microscopes?

Viewing the cornea of the eye.

Two types of electron microscopes

- Transmission electron microscope

- Scanning electron microscope

What are the disadvantages of using a transmission electron microscope? (5)

- Specimen has to be chemically fixed, dehydrated and stained.

- Only dead organisms can be used due to a vacuum being used.

- relatively expensive

- users need to be trained to use the machine

- not portable

What are the advantages of using a scanning electron microscope?

- 3D image is formed in black and white.

- Compared to a light microscope, magnification and resolution is improved

- (False colour can be added, however image colour produced is black and white)

What are the disadvantages of using a scanning electron microscope?

- Vacuum needs to be generated so organisms also need to be dead.

- relatively expensive

- users need to be trained to use the machine

- not portable

What is the magnification and resolution of Scanning electron microscopes for the A level exam?

Magnification is X100,000

Resolution is 10nm

What is the magnification and resolution of Transmission electron microscopes for the A level exam?

Magnification is X500,000

Resolution is 0.5 nm

What is the magnification and resolution of light microscopes for the A level exam?

Magnification is X1500

Resolution is 200 nm

Which colour is images produced for laser scanning, SEM or TEM microscopes?

- TEM and SEM produce pictures in black and white

- Laser scanning microscope produces images in colour

What does the term differential staining mean?

Stains that bind to certain structures

What features must biological drawings have?

- Magnification/scale bar

- Title

- Labels

- No shading/cross-hatches

What stain binds to DNA and stains chromosomes red

acetic orecin (dark red)

What stain stains the cytoplasm?

eosin

What stain stains lipids

Sudan red

What stains cellulose yellow and starch granules blue/black

Iodine in potassium iodide solution

Why would some microscopes use light interference instead of light absorption?

To produce a relatively clearer image without the need to stain, useful for viewing live organisms

Why would two different cells have their structures (i.e. cytoplasms) bind differently to the same stain? (This will vary from structure to structure)

- r/t/m RNA present

- More/less proteins

- Different levels of activity

How should you place a stain on a sample?

Place stain at the edge of the sample

How could you further increase contrast of a sample when you have already used one stain?

Use more than one stain.

How are prepared specimens made? Scroll down after flipping card.

1) Specimen is dehydrated

2) Specimen placed in wax to prevent distortion

3) Sections (thin slices) made of specimen

4) Sliced specimen is stained

5) Specimen embedded in a preservative chemical

6) Specimen mounted

What features must be made sure when preparing slides?

- A sharp blade needs to be selected

- Select thinest slides; ensures maximum light can penetrate the sample

- Wet mount; also prevents distortion of sample

- Squash slide; easier to see individual slides

Using a photomicrograph, what is the equation to calculate image size

Image size = magnification * actual size

Why would a cell need a double membrane organelle?

To have discrete compartmentalisation

How does the structure of the Rough Endoplasmic reticulum relate to its function?

- Phospholipid molecules form phospholipid bilayer known as the membrane

- System of the phospholipid bilayer forms membranes containing cisternae (long cavities)

- Coated with ribosomes

- This allows the ribosomes to be transported in the cisternae to be pinched off as a vesicle

How does the structure of the Smooth Endoplasmic reticulum relate to its function?

Cisternae contains enzymes that allow the catalysing and transportation of lipids

What three types of lipids can be synthesised by the SER?

- Cholesterol

- Phospholipids

- Steroid hormones

How does the structure of the golgi apparatus relate to its function

- Allows proteins to be modified and packaged

- Stack of membrane bound flattened sacs with secretory vessels (this is what packages proteins into vesicles)

Examples of how are proteins are modified in the Golgi apparatus? (3)

- Sugar molecules added to form glycoproteins

- Lipid molecules added to form lipoproteins

- polypeptides folded further into their 3D shape

What is the process of how proteins are packaged and released?

Proteins are packaged into their vesicles and released via secretory vessels

What are two fates of vesicles after being secreted in the cell?

- Stored in the cell cytoplasm

- Exported to the cell surface membrane.

What are the fates of vesicles if they are sent to the cell surface membrane?

- Exported to the cell surface membrane

- Incorporated with the membrane itself released via exocytosis

What is the structure of the mitochondrion?

- Has a double membrane,

- Inner membrane highly folded into structures called cristae

- Inner part of mitochondrion is filled with fluid-filled matrix

What is the structure of cilla and how are they formed?

- Contains receptors

- Formed from centrioles and each contains microtubules

What is the structure of ribosomes?

- Small spherical organelles

Where are ribosomes molecules made and what from?

- Made in the nucleolus

- Made from ribosomal RNA

- ribosomes formed outside of nucleus

What is the fate of ribosomes after being released from the nucleolus?

- Remain free in cytoplasm

- Connect to the rough endoplasmic reticulum

What is the function of ribosomes?

- To synthesise proteins (translation) before the proteins are exported out the cell.

- To synthesise proteins (translation) before the proteins are used in the cell.

- To stay bound to the rough endoplasmic reticulum

What is the structure of the cytoskeleton, i.e. what smaller structures is it made of?

Made of;

- Microfilaments (made of actin), each 7nm in diameter

- Intermediate filaments, 10 nm in diameter

- Microtubules made of tubulin, 18-30 nm in diameter

- Cytoskeletal motor proteins

What do microfilaments do?

- Give cell support

- Give cell mechanical strength

- Helps cell stability

- Helps cell movement

What do intermediate filaments do?

- Anchor the nucleus in the cytoplasm

- extend between multiple cells in some tissues

What is the purpose of intermediate filaments extending between multiple tissues?

- Enables cell signalling

- Stabilises tissues of multiple cells (provides tissue strength)

What do Microtubules do within the cytoskeleton?

- Helps substances and organelles move through the cytoplasm in the cell.

- Give cell support and mechanical strength further

- Helps cell stability and movement further

What proteins does the cytoskeletal molecular motors consist of?

- Consist of myosins, kinesics and dyenins.

What are the cytoskeletal molecular motors and their proteins primary functions?

- Motor proteins drag organelles from one part of the cell to the other

- Molecular proteins act as enzymes, having an active site for hydrolysis of ATP

How are organelles moved around the cell?

- Cytoskeletal motor proteins use ATP as energy to attach to the organelle

- Drag organelles across the cell

What is the structure of lysosomes and what do they contain?

- Small bags

- contain powerful hydrolytic enzymes.

Where are lysosomes formed from?

From the Golgi apparatus

What is the function of lysosomes?

- Keep powerful hydrolytic digestive enzymes separate from the rest of the cell, compartmentalisation

- Engulf and destroy old organelles

- Destroy foreign bodies (such as pathogens)

Where are lysosomes abundant?

In phagocytic cells

What is the structure of chloroplasts?

- Surrounded by a double membrane or envelope.

- Contains loops of DNA and starch grains.

- Inner membrane has stacks of thylakoids containing chlorophyll (grana).

- Fluid-filled matrix is called the stroma.

Where are chloroplasts found?

Found only in plant cells and some protoctists.

How long are chloroplasts?

4-10 micrometers long.

What are the functions of chloroplasts?

- Provide the site of photosynthesis;

- First stage is light-dependent where the chlorophyll traps ATP. Photolysis occurs

- Second stage is light independent where NADPH reduces CO2 with energy from ATP to form carbohydrates.

What is the structure of a vacuole?

- Surrounded by a membrane called the tonoplast

- Filled with a sap-like solution with sugar and salts.

What is the function of the vacuole?

- Maintains cell stability when filled with water and solutes.

- When turgid it pushes against the cell wall

What type of cells have a large vacuole?

Only plant cells have a large vacuole.

What is the structure of the cell wall in plant cells?

- On outside of plasma membranes

- Made from a bundle of cellulose fibres.

What are the functions of the cellulose cell wall?

- Prevent the plant cell from bursting when turgid

- Provides strength and support

- Prevent pathogens from entering the cell

- Maintains the cell shape

- To be permeable for solutions to pass through

How many steps are there of the secretion of a protein?

Nine. Give or take.

First three steps for the making and secretion of a protein?

1) Gene that has coded instructions for a protein is transcribed into a length of mRNA in the nucleolus

2) mRNA leaves the through a nuclear envelope pore out of the nucleus

3) mRNA attaches to a ribosome, allowing translation and protein (i.e. insulin) molecules are assembled

Next three steps for the making and secretion of a protein?

4) Protein (i.e. insulin) molecules pass through the cisternae of the Rough Endoplasmic reticulum along hollow sacs to then become a vesicle

5) Vesicles with the protein inside are pinched off from the Rough endoplasmic reticulum and travel towards the Golgi apparatus

6) Vesicles fuse with the Golgi apparatus. Protein molecules can be modified

Final three steps for the making and secretion of a protein?

7) Packaged and modified vesicles pinched off the Golgi apparatus' secretory vessels' .

8) Vesicles fuse with plasma membrane

9) The protein is released by exocytosis or used in plasma membrane

What are some structures both Eukaryotic cells and Prokaryotic cells both attain

- A cell-surface membrane

- A Cytoplasm

- Ribosomes

- DNA

- RNA

Differences between eukaryotic and prokaryotic cells

- Prokaryotic cells are much smaller than Eukaryotic cells

- Prokaryotic cells have moreso well-developed cytoskeleton than Eukaryotic cells

- Prokaryotic cells have no centrioles, Eukaryotic does

- Prokaryotic cells have no nucleus, Eukaryotic does

- Prokaryotic cells does not have membrane bound organelles unlike Eukaryotes (mitochondria, endoplasmic reticulum, chloroplasts, etc)

- Prokaryotes have a cell wall made out of peptidoglycan whereas Plants (eukaryote) have a cell wall made out of cellulose

- Prokaryotic cells have smaller ribosomes than Eukaryotes

- Prokaryotic cells have naked DNA that floats free in the cytoplasm as a loop. Eukaryotic has a nucleus

What are the three main differences between a plant cell and an animal cell?

- Plant cells contain a large vacuole, animal cells contains small vacuoles

- Plant cells contains chloroplasts, animal cells do not contain chloroplasts

- Plant cells contains a cellulose cell wall, animal cells do not contain a cellulose cell wall

How do prokaryotic cells divide?

By binary fission

What is binary fission?

- A form of asexual reproduction

- Parent cell divides into two approximately equal daughter cells

Why can't prokaryotic cells divide by mitosis?

They do not have linear chromosomes.

What is a feature of when prokaryotes divide by binary fission?

Their DNA is copied so each new cell receives a large loop of DNA and any smaller plasmids

How do yeast divide?

By budding

Are viruses made up of a cell(s)

No. They do not possess any cells!