(A) Cell Structure and Division - 3.2

What organelles are found in animal cells?

1. Lysosome

2. Rough ER

3. Smooth ER

4. Nucleus

5. Golgi Apparatus

6. Mitochondria

7. Cytoplasm

8. Ribosomes

9. Cell-surface Membrane

What organelles are found in plant cells?

1. Lysosome

2. Rough ER

3. Smooth ER

4. Nucleus

5. Golgi Apparatus

6. Mitochondria

7. Cytoplasm

8. Ribosomes

9. Cell-surface Membrane

10. Vacuole

11. Cell Wall

12. Chloroplasts

What are the similarities and differences between algal cells and plant cells?

Similarities: They have the same organelles.

Differences: Algal cells have one large chloroplast as opposed to several smaller chloroplasts.

What are the differences between fungal cells and plant cells?

1. Fungal cell walls are made of chitin instead of cellulose.

2. Fungal cells don't have chloroplasts as they don't photosynthesise.

What is the structure of cell-surface membranes (plasma membranes)?

1. They are membranes on the surface of animal cells and inside the cell wall of other cells.

2. They are made of phospholipids.

What is the function of cell-surface membranes (plasma membranes)?

1. Control which substances leave and enter cells.

2. Barrier between cells and their environments.

3. Contains receptor proteins to detect chemicals released by other cells.

What 5 components makes up the nucleus?

1. Nuclear envelope

2. Nuclear pores

3. Nucleoplasm

4. Nucleolus

5. Chromosomes

Describe the structure and function of the nuclear envelope in the nucleus?

1. It is a double membrane that surrounds the nucleus.

2. Its outer membrane merges with the endoplasmic reticulum, so it may have ribosomes on its surface.

3. It controls the entry and exit of materials in and out the nucleus.

Describe the structure and function of the nuclear pores in the nucleus?

Allows substances like RNA to move between the nucleus and the cytoplasm.

Describe the structure and function of the nucleoplasm in the nucleus?

It is a jelly-like material that makes up the majority of the nucleus.

Describe the structure and function of the nucleolus in the nucleus?

1. It is a small spherical region in the nucleus.

2. It manufactures ribosomal RNA and assembles ribosomes.

Describe the structure and function of the chromosomes in the nucleus?

It is a protein-bound linear DNA.

What is the function of the nucleus?

1. Controls the cells' activities through the production of mRNA and tRNA for protein synthesis.

2. Manufactures ribosomal RNA and ribosomes.

3. Retains the cell's genetic information in the form of DNA and chromosomes.

What is the structure of the mitochondria?

1. It has a double membrane.

2. The inner membrane folds to form cristae which provide a large surface area for the attachment of enzymes and other proteins in respiration.

3. It contains a matrix which contains enzymes involved in respiration, and contains proteins, lipids, ribosomes and DNA that allow the mitochondria to control the production of some of their own proteins.

What is the function of the mitochondria?

It is the site of aerobic respiration, so produces ATP.

Why are mitochondria found in large numbers in some cells?

They are found in cells that are very active so require a lot of energy.

What is the structure of chloroplasts?

1. It contains a chloroplast envelope which is a double membrane that surrounds the cell and controls what enters and leaves it.

2. It contains grana that are stacks of disc-like structures called thylakoids that contain the photosynthetic pigment, chlorophyll. The grana are held together by intergranal lamella.

3. It contains stroma which is a fluid-filled matrix where sugars are synthesised.

What is the function of chloroplasts?

It is the site of photosynthesis.

What are the adaptations of chloroplasts?

1. Grana provide a large surface area for attachment of chlorophyll.

2. Stroma contains the enzymes needed to make sugar during the second stage of photosynthesis.

3. Contains both DNA and 70S ribosomes so it can quickly manufacture the proteins needed for photosynthesis.

What is the structure of the endoplasmic reticulum?

It is a system of sheet-like membrane which contain a network of tubules and flattened sacs called cisternae.

Describe the structure and function of the rough endoplasmic reticulum?

1. It contains ribosomes on its outer surface.

2. It provides a large surface area for the synthesis of proteins by ribosomes.

3. It folds and processes proteins made at ribosomes providing a pathway for protein transport.

Describe the structure and function of the smooth endoplasmic reticulum?

1. It synthesises, stores and transports lipids.

2. It synthesise, stores and transports carbohydrates.

What is the structure of the Golgi apparatus?

It is made up of cisternae with small rounded hollow structures called vesicles.

What is the function of the Golgi apparatus?

1. Adds carbohydrates to proteins to form glycoproteins.

2. Produces secretory enzymes.

3. It secretes carbohydrates.

4. It transports, modifies and stores lipids.

5. It forms lysosomes.

What produces the Golgi vesicle?

The Golgi apparatus.

What is the structure of Golgi vesicles?

It is a small fluid-filled sac in the cytoplasm, surrounded by a membrane.

What is the function of the Golgi vesicle?

It stores lipids and proteins processed by the Golgi apparatus and transports them out of the cell via the cell-surface membrane.

What is a lysosome?

A type of Golgi vesicle.

What is the function of a lysosome?

1. It contains a digestive enzyme called lysozymes that hydrolyse the cell wall of certain bacteria.

2. They fuse with a vesicle, then can be used to digest invading cells or break down worn out components of the cell.

What are the two types of ribosomes and where are they found?

1. 80S - found in eukaryotes.

2. 70S - found in prokaryotes, mitochondria and chloroplasts and is smaller than an 80S.

What are ribosomes?

1. They are a small organelle that floats freely in the cytoplasm or is attached to the Rough Endoplasmic Reticulum.

2. They are made of proteins and RNA.

3. They do not have a membrane.

4. They contain 2 subunits, one large and one small.

What is the structure of the cell wall?

1. Plants and algae cell walls are made of cellulose.

2. Fungal cell walls are made of chitin.

3. They have a thin layer called middle lamella which marks the boundary between adjacent cell walls.

What is the function of the cell wall?

1. It provides strength to prevent the cell from bursting under pressure by osmotic entry of water.

2. Supports the cell by strengthening it.

What is the structure of the cell vacuole?

1. It is a fluid-filled sac bound by a single membrane called tonoplast.

2. Contains cell sap, which is a weak solution of sugars and salts.

What is the function of the cell vacuole?

1. Maintains pressure inside the cell to keep it rigid and prevent wilting.

2. Its pigments colour petals so they attract pollinating insects.

What is the role of organelles in the production, transport and release of proteins from eukaryotic cells?

1. The DNA in nucleus is the code for protein.

2. The ribosomes/rough endoplasmic reticulum produce proteins.

3. The mitochondria produce ATP for protein synthesis

4. The Golgi apparatus adds a carbohydrate to the protein forming a glycoprotein.

5. The vesicles transport the protein.

6. The vesicles fuse with the cell-surface membrane.

How do genes affect cell differentiation in multicellular organisms?

Different genes are switched on or off in different cells so that they can differentiate.

What is the function of epithelial tissues in the small intestine?

They are adapted to absorb food efficiently.

What is a glycoprotein?

A protein with carbohydrate attached to it.

What are the organelles in a prokaryote?

1. Cytoplasm

2. Ribosomes

3. Cell-Surface Membrane

4. Cell wall

5. Slime Capsule

6. Plasmid

7. Circular DNA

8. Flagellum

Are there membrane-bound organelles in cytoplasm in prokaryotes?

No.

What size ribosomes are in prokaryotes?

70S ribosomes.

What is the function of the cell-surface membrane in prokaryotes?

They control the movement of substances in and out of the cell.

What is the structure and function of the cell wall in a prokaryote?

1. It supports the cell and prevents it from changing shape.

2. It is made of a polymer called murein, which is a glycoprotein.

What is the function of the slime capsule on prokaryotes?

It helps to protect the bacteria from attack by cells of the immune system.

What are plasmids?

1. They are small loops of DNA.

2. Some prokaryotic cells have several of them.

What are flagellum?

1. It is a long structure used to make the prokaryotic cell move.

2. Not all prokaryotes have them and some have more than one.

What do prokaryotes have instead of a nucleus?

They have free-floating circular DNA

What is the name of the process by which a prokaryote divides?

Binary fission.

How does binary fission work?

1. The circular DNA and plasmids replicate, with the circular DNA replicating once and the plasmids replicating multiple times.

2. The cell increases in size and the circular DNA loops move to the opposite poles (ends) of the cell.

3. Cytoplasm starts to divide.

4. New cell walls begin to form.

5. Cytoplasm divides and two daughter cells are produced, each daughter with one copy of circular DNA, but a variable number of plasmids.

What are viruses?

Acellular, non-living, nucleic acid surrounded by protein.

What are the cells that viruses invade and reproduce in called?

Host cells.

What components make up viruses?

1. Capsid - protein coat

2. Genetic material (DNA or RNA)

3. Attachment proteins

Do viruses replicate via cell division?

No.

How do viruses replicate?

1. The virus attaches to the host cell's receptor proteins using its complimentary attachment proteins.

2. They then inject their genetic material (DNA or RNA) into the host cell.

3. They use the host cell's machinery to replicate their genetic material and proteins.

4. The viral components are assembled and they are released from the host cell via lysis.

What is magnification?

How many times larger the image is than the actual size of the specimen/object.

What is resolution?

The minimum distance that two objects are apart, so that they appear as separate objects.

How do optical (light) microscope form an image?

They use light to form an image.

How do electron microscopes form an image?

They use electrons to form an image.

How does the resolution and magnification compare between optical and electron microscopes?

1. Optical microscopes have a lower magnification with a maximum of x1500, whereas electron microscopes have a higher magnification with a maximum of x1500000.

2. Optical microscopes have a lower resolution with a maximum of 0.2 μm, whereas electron microscopes have a higher resolution with a maximum of 0.0002 μm.

Why do light microscopes have a poor resolution?

As a result of the relatively long wavelength of light.

What does a shorter wavelength mean for microscopes?

The shorter the wavelength, the higher the resolving power.

What are the two types of electron microscopes?

1. Transmission electron microscope (TEM).

2. Scanning electron microscope (SEM).

How do TEMs form an image?

1. They focus a beam of electrons which is transmitted through the specimen.

2. The specimen will absorb electrons.

On TEM microscopes, why do parts of the image look darker?

Denser parts absorb more electrons making it darker.

How do SEMs form an image?

1. They scan a beam of electrons across the specimen.

2. This knocks off electrons from the specimen which gather in the cathode ray tube to form an image.

What are the advantages and disadvantages of TEMs?

Advantages:

They give high resolution images, so they show small objects.

Disadvantages:

1. Can only be used on thin specimens.

2. No colour.

3. They must be in a vacuum so can only be used on non-living specimens.

What are the advantages and disadvantages of SEMs?

Advantages:

1. They can be used on thick specimens.

2. The images show the surface of the specimen so they can shows 3D images.

Disadvantages:

1. They give lower resolution images than TEMs.

2. This can only be used on non-living specimens

What are microscope artefacts and give some examples?

They are things you can see down the microscope that aren't part of the cell or specimen you're looking at (e.g. air bubbles or fingerprints).

Why are artefacts especially common in electron micrographs?

They need a lot of preparation before you can view them under an electron microscope, so there is more time for artefacts to enter the specimen.

How did the first scientists distinguish between artefacts and organelles?

They repeatedly prepared specimens in different ways to view them.

What is the purpose of cell fractionation?

To extract organelles in order to look at them.

What conditions must a solution be in and why before it undergoes cell fractionation?

1. Ice cold - To reduce enzyme activity so that the organelles are not broken down by enzymes.

2. Add buffer solution - To maintain the pH to prevent the enzyme being denatured.

3. Isotonic/Same water potential - To prevent osmosis so there is no lysis of the organelles.

What is the first stage in cell fractionation and explain it?

1. It is homogenisation, which is where the solution containing the sample is mixed in a blender to break up the plasma membrane which breaks open the cells and then releases the organelles into the solution.

2. The resultant fluid is called homogenate.

What is the second stage in cell fractionation and explain it?

The solution is filtered through a gauze to remove any unbroken cells or larger debris from the cells or tissue.

What is the third stage in cell fractionation and explain it?

1. It is ultracentrifugation.

2. The homogenate solution is placed in a centrifuge and spun at a slow speed.

3. The heaviest organelles, the nuclei, are forced to the bottom of the tube where a thin sediment or pellet forms.

4. The fluid at the top, the supernatant, is removed which leaves just the sediment of the nuclei.

5. Drain the supernatant and then transfer it to another tube and spin it at a slightly faster speed.

6. This time the pellet that forms contains the next heaviest organelle, the mitochondria.

7. This process continues so that each time the speed is increased the next heaviest organelle is sedimented and separated out.

What is the order of organelles from heaviest to lightest?

1. Nuclei

2. Chloroplasts

3. Mitochondria

4. Lysosomes

5. Endoplasmic Reticulum (ER)

6. Ribosomes

How do organelles separate during ultracentrifugation?

1. They separate depending on their molecular mass/density.

2. Lighter organelles have a lower density.

What 3 stages make up the cell cycle?

1. Interphase

2. Mitosis

3. Cytokinesis

What happens during interphase?

1. G1 - The cell grows and new organelles and proteins are made.

2. S (Synthesis) - The cell replicates its DNA so that it is ready to divide by osmosis.

3. G2 - The cell grows and the proteins needed for cell division are made.

4. The ATP content is increased to provide the energy needed for cell division.

What is a synopsis of mitosis?

A parent cell divides to produce two genetically identical cells, containing an exact copy of the DNA from the parent cell.

What is the purpose of mitosis in multicellular organisms?

1. Growth.

2. Repairing damaged tissues.

What components make up chromosomes?

1. Centromere

2. Chromatids

3. Chromatin

What are the 4 stages of mitosis?

1. Prophase

2. Metaphase

3. Anaphase

4. Telophase

What happens during the prophase?

1. The chromosomes condense, so they get thicker and shorter.

2. Centrioles start to move to opposite ends of the cell, forming the spindle fibres.

3. The nuclear envelope begins to break down.

4. The chromosomes are arranged randomly in the cytoplasm as the spindle fibre isn’t formed yet.

What happens during the metaphase?

1. The chromosomes line up along the centre of the cell.

2. The chromosomes become attached to the spindle fibres by the centromere.

What happens during anaphase?

1. The centromere divides, and the chromatid pairs separate.

2. The spindle contracts and the chromatids are pulled to opposite poles of the spindle.

What happens during telophase?

1. The chromatids reach the opposite poles of the cell.

2. They uncoil and become long and thin, and are now chromosomes.

3. A nuclear envelope forms around each group of chromosomes, forming two nuclei

What happens in cytokenesis?

1. The cytoplasm divides and two genetically identically daughter cells are formed.

2. These cells are genetically identical to the original cell.

What is cancer?

Uncontrolled cell division of abnormal cells leading to the formation of tumours and eventually cancer.

How is cancer formed?

If there is a mutation in the gene that controls cell division, the cell can grow out of control.

What are cancer treatments designed to do?

They control the rate of cell division in the tumour by disrupting the cell cycle, which kills tumour cells.

What is a basic summary of how a microscope slide is prepared during the mitosis practical?

1. Cut the first 5mm from the tip of an onion root and place it on a glass slide.

2. Cover this tip with a drop of stain solution and a cover slip.

3. Warm the glass slide.

4. Press down hard on the cover slip.

Why are only the first 5mm cut from the root tip when a microscope slide is prepared?

1. It is where the cells are dividing.

2. It is used to get the soft tissue that will squash.

3. It is a length that will fit under the cover slip.

Why is the cover slip pressed down hard, when a microscope slide is prepared?

So that a single, thin layer of cells are spread out, so that light passes through making the cells and nuclei visible.

Why isn’t the cover slip placed down sideways, when a microscope slide is prepared?

To avoid the cells rolling together and breaking the chromosomes.

How do you make a temporary mount of a sample?

1. Add a drop of water to the glass slide.

2. Obtain thin section of tissue and place on slide.

3. Stain with potassium iodide.

4. Lower the cover slip using a mounted needle.

What is the mitotic index?

The proportion of cells in a tissue sample that are undergoing mitosis.

What is the equation for mitotic index?

Mitotic index = (number of cell with visible chromosomes)/(number of cells observed)