2.1.1 Cell Structure

Question 1

What are cells?

Answer 1

Basic unit of life.

Question 2

What is a eukaryote?

Answer 2

Organism consisting of eukaryotic cells.
Eukaryotic cells contain DNA in a nucleus separated from the cytoplasm.
They contain a large number of specialized membrane bound organelles.

Question 3

What are the nucleus, nucleolus and nuclear envelope?

Answer 3

The nucleus contains chromosomes (in a loosely coiled state known as chromatin (DNA + histone proteins)) which are made from DNA.
The nucleus is surrounded by a nuclear envelope (made of a double membrane).
The nucleolus contains RNA and is where ribosomes are made.
Nuclear pores allow things to move inside and outside the nucleus

Question 4

What is the smooth endoplasmic reticulum?

Answer 4

Endoplasmic reticulum without ribosomes on its surface.
Synthesis of lipids, cholesterol and steroid hormones.
Absorb and transport lipids from the gut.
Contains enzymes that detoxify.

Question 5

What is the rough endoplasmic reticulum?

Answer 5

System of membrane sacs (cisternae) filled with fluid.
Studded with ribosomes.
Intracellular transport.
Ribosomes make proteins which are transported within the ER.

Question 6

What is the golgi apparatus?

Answer 6

Series of tightly packed flattened cisternae.
Collects and processes proteins by:
- Adding sugar (glycoproteins)
- Adding lipids (lipoproteins)
- Folds into 3D shape
The proteins are packaged into vesicles and will:
- Stay in the cell and is stored (lysosomes)
- Be incorporated into the plasma membrane
- Be exported outside of the cell (exocytosis)
Transport vesicles come from RER to the forming face of the Golgi and bud off the maturing face.

Question 7

What are lysosomes?

Answer 7

Contain powerful hydrolytic/digestive enzymes.
Appear as darkly staining spheres.
Destroy damaged organelles and cells so the components can be reused.
Found in white blood cells and acrosome.

Question 8

What are centrioles?

Answer 8

Found in animal cells.
Microtubules made of protein (tubulin).
Found outside of nucleus in pairs set at right angles to each other.
Produce spindle fibres which attach to the centromere of the chromosome during cell division.

Question 9

What are undulipodia and cilia?

Answer 9

Protrude from cell surface surrounded by cell membrane.
Contain microtubules.
If short and numerous they are cilia.
If long and few in number they are undulipodia.

Question 10

What are mitochondria?

Answer 10

They have an envelope.
Inner membrane highly folded to form cristae which project into internal solution (matrix).
They make ATP during aerobic respiration.
Can replicat themselves.

Question 11

What are chloroplasts?

Answer 11

Surrounded by envelope.
Flattened sacs or thylakoids run through the internal solution (stroma).
The sacs are stacked (grana)
Site of photosynthesis.

Question 12

What is plasmodesmata?

Answer 12

Channels/pores between adjacent plant cells.
Facilitate communication and transport of materials.

Question 13

What is a vacuole?

Answer 13

Surrounded by tonoplast.
Fluid contains water and solutes.
Permanent only in plant cells.
Maintains cell turgidity.
Support the plant.

Question 14

What is the cell wall?

Answer 14

Made of cellulose in plants and chitin in fungi.
Provide strength and support for whole plant.
Maintain cell shape.
Permeable.

Question 15

What are ribosomes?

Answer 15

Made of protein and rRNA.
One large and one small subunit.
Made in nucleolus.
Make proteins.

Question 16

What is the role of the cytoskeleton?

Answer 16

Actin microfilaments:
- Support and mechanical strength.
- Maintain cell shape.
- Allow cell movement.
Microtubules:
- Make up track where motor proteins transport organelles along.
- Form spindle and move chromosomes during mitosis.
Intermediate filaments:
- Anchor the nucleus in the cytoplasm.
- Communication and signalling between cells.
- Adhere the cell to the basement membrane.

Question 17

Language of genetic information.

Answer 17

DNA - contains the whole genetic code
Chromosome - structure of tightly coiled DNA in the nucleus
Gene - section of DNA that codes for a specific protein

Question 18

How are proteins produced and secreted?

Answer 18

1. mRNA copy of gene for protein made in nucleus
2. mRNA leaves nucleus through nuclear pore
3. mRNA attaches to ribosome which reads instructions to assemble protein
4. Protein molecules pinched off in vesicles and travel to golgi apparatus
5. Membrane of vesicle fuses with golgi apparatus
6. Golgi processes and packages protein molecules
7. Protein molecules pinched off in vesicles and travel towards plasma membrane
8. Membrane of vesicle fuses with plasma membrane (EXOCYTOSIS)
9. Plasma membrane opens to release/secrete protein molecules outside (EXOCYTOSIS)

Question 19

How is genetic information stored in prokaryotic cells?

Answer 19

Bacteria and archaea do not have a membrane bound nucleus like eukaryotic cells.
Genetic information is stored in a free-floating loop of DNA called the nucleoid.
They also have a smaller circular loop called the plasmid.

Question 20

Bacterial cell wall.

Answer 20

Made of peptidoglycan (murein)
Some also have capsule allowing cell to cause disease and prevent destruction.

Question 21

Pili (prokaryotic cells).

Answer 21

Small protrusions used for communication between bacterial cells.
Allow for exchange of plasmids.
NOT ALL BACTERIA CONTAIN PILI.

Question 22

Mesosome (prokaryotic cells).

Answer 22

Infolded regions of inner membrane.
Site of respiration.

Question 23

Ribosomes (prokaryotic cells).

Answer 23

Smaller 70s ribosomes.

Question 24

Flagella (prokaryotic cells).

Answer 24

For locomotion.

Question 25

How do prokaryotic cells divide?

Answer 25

By binary fission.
Asexual reproduction resulting in two identical daughter cells.
NO NUCLEAR ENVELOPE TO BREAK DOWN AND NO SPINDLE FIBRES PRESENT.

Question 26

What is the difference between magnification and resolution?

Answer 26

Magnification - the number of times larger an image appears, compared with the size of the object.
Resolution - the ability to distinguish between separate points. (If two points cannot be resolved they are considered as a single point).

Question 27

Light (optical) microscopes.

Answer 27

Pros:
- Cheap
- Easy to use
- Portable
- Observe living specimens
Cons:
- Max magnification usually x1500
- Resolution limited due to wavelength of light

Question 28

Transmission EM.

Answer 28

Pros:
- High resolution (uses electrons)
- High magnification (x50,000,000)
Cons:
- Dead samples
- Large
- Expensive
- Need training to use

Question 29

Scanning EM.

Answer 29

Pros:
- High magnification (x200,000)
- High resolution
- 3D image
Cons:
- Dead samples
- Large
- Expensive
- Need training to use
- Metallic stains (hazardous)
- Cannot show organelles in 3D

Question 30

Laser scanning microscopes (confocal).

Answer 30

• High resolution
• Can focus on structures at different depths
• Observe living specimens

Question 31

How to prepare slides.

Answer 31

Dehydration - water removed using ethanol.
Embedding - supports tissue in wax or resin so it can be cut into thin sections.
Sectioning - produces very thin slices for mounting. Sections cut with microtome or ultramicrotome.
Mounting - protects material so its suitable for viewing over a long period.

Question 32

Why is staining done?

Answer 32

Provides contrast to distinguish between different structures in sample.
Differential staining - more than one stain is used, each stain binds to a specific cell structure.