Cells and organelles

Question 1

What is a prokaryote

Answer 1

They are 1-10um. They are simple, single celled organisms without a nucleus and membrane bound organelles

Question 2

Where are genetic materials found in prokaryotes

Answer 2

In the central region known as the nucleoid

Question 3

What is a eukaryote

Answer 3

10-100um. They are more complex with multiple chromosomes in the nucleus. They are multicellular

Question 4

What are the properties of cells

Answer 4

They act as independent units. They originate from pre-existing cells by replication. They can adapt and respond

Question 5

What is the plasma membrane

Answer 5

It is a protective sheath that encloses the cell as an independent reaction container. It separates the intracellular fluid (ICF) from the extracellular fluid (ECF). It is semipermeable regulating the exchange of molecules between the ICF and ECF. It has a bilayer of lipid molecules with associated protein molecules

Question 6

What is the structure of the cell membrane

Answer 6

They are phospholipids which consist of 2 hydrophobic fatty acid chains linked to a phosphate containing hydrophilic head

Question 7

What is the function of the phospholipids

Answer 7

They provide basic and fundamental structure of membranes forming a stable barrier between 2 aqueous compartments

Question 8

What is the function of embedded cholesterol

Answer 8

It exists in the lipid bilayer with a polar hydroxyl group. It provides the membrane with fluidity/rigidity

Question 9

What are linking proteins

Answer 9

They give structure to the plasma membrane. They also hold the cells together and participate in movement

Question 10

Difference between protein expression in prokaryotes and eukaryotes

Answer 10

In pros, DNA is packaged but not enclosed by the membrane. In euks, DNA is packaged and enclosed by a double membrane

Question 11

Describe protein expression in eukaryotic cells

Answer 11

• DNA transcribed to produce mRNA
• mRNA (message) passes from the nucleoplasm to the cytoplasm via holes called nuclear pores.
• mRNA is decoded and proteins made (translation) on specialised factories called the ribosomes.

Question 12

What is the function of histones

Answer 12

They package DNA forming a complex called chromatin

Question 12

How is chromatin packaged

Answer 12

Euchromatin (active genes) and a more dense heterochromatin (inactive genes)

Question 12

What are nuclear pores

Answer 12

Selective aqueous channels for transport between nucleus and cytosol (mRNA passage but also in both directions)

Question 13

Describe protein synthesis

Answer 13

• All protein synthesis starts in the cytosol
• First stretches of any proteins destined for ER/Golgi processing are recognised and ribosome becomes bound to ER to generate ER coated with ribosomes – RER
• Signal sequence (short stretch of amino acids) targets the newly made protein to the RER

Question 14

What is the function of the RER

Answer 14

• Site of membrane synthesis (lipids and proteins)
• Modifies proteins – adds sugar chains, trims them (proteolytic cleavage), disulfide bond formation
• Quality control
• Signals stress – e.g., when secretion is blocked/poorly folded proteins.

Question 15

What is the function of the SER

Answer 15

The (SER) is free of ribosomes. The SER is common in cell types active in lipid metabolism. The SER is involved in:
- Lipid synthesis.
- No protein synthesis
- Steroid synthesis
- Detoxification

Question 16

Describe the secretory pathway

Answer 16

• Vesicles carry “cargo” from RER to the Golgi.
• Cargo proteins are processed and sorted in the Golgi.
• Some vesicles can bud from Golgi containing packaged (stored) secretory proteins.
• Other vesicles bud from Golgi with membrane for the PM (Constitutive vesicles).