Lecture 8

Question 1

What does the smooth ER not have?

Answer 1

Attached ribosomes

Question 2

What are the functions of the smooth ER?

Answer 2

• Lipid synthesis (production of phospholipids and cholesterol)
• Steroid synthesis and secretion (hormones that are produced by the adrenal glands, testis and ovaries)
• Metabolism of carbohydrates (blood glucose levels)
• Detoxification (including drug breakdown) (degrades these harmful chemicals into less harmful water soluble components, which is due to enzymes in the lumen of the smooth ER)
• Ca2+ accumulation e.g. skeletal muscle cells (sarcoplasmic reticulum)

Question 3

What are the two main mechanisms used to keep blood glucose levels from dropping too low (hypoglycemia)?

Answer 3

Glycogenolysis:
- Muscle & liver
- Glycogen converted to
glucose
- Smooth ER contains glucose-6-phosphatase
- Converts glucose-6-phosphate to glucose

Gluconeogenesis
- Glucose production from non carbon sources

Question 4

What is the sarcoplasmic reticulum?

Answer 4

• Specialization of smooth ER found in smooth & striated muscle
• Storage & release of Ca2+
• Under the influence of excitable membranes (neurons)
• Role in Excitation-Contraction Coupling (ECC)

Question 5

Smooth ER vs Rough ER?

Answer 5

Smooth:

• Has no ribosomes
• Makes and stores lipids and steroids

Rough:

• Covered in ribosomes
• Makes and stores proteins

Both:
- Make cellular material

Question 6

What are the protein factories of the cells?

Answer 6

Ribosomes:

• Catalyse the assembly of protein chains
• Small, dense, functional structure found in all known cells that assemble proteins

Question 7

What are ribosomes composed of?

Answer 7

ribonucleoprotein and ribosomal RNA

Question 8

Where are ribosomes found and made?

Answer 8

The nucleolus

Question 9

What do ribosomes do?

Answer 9

• Reads mRNA (translates)
• Binds amino acids attached to transfer RNA molecules (tRNA)

(Translates mRNA to produce polypeptide chains)

Question 10

What are the two unequal subunits that ribosomes are made of?

Answer 10

• Large subunit

- Small subunit

Question 11

Describe the molecular basis of the ribosome 60S and 40S subunit structure.

Answer 11

These are the two unequal subunits that ribosomes are made of:
Small subunit - 40 Svedberg units
Large subunit - 60 Svedberg units
Combined (40S + 60S) = 80 Svedberg units

The rate at which they settle

Question 12

Svedberg units?

Answer 12

• Unit of measurement known as the sedimentation rate
• When you spin it around, the speed at which a molecule sediments (settles) is divided by the acceleration of the centrifuge

Question 13

What is nucleolar organiser DNA?

Answer 13

It codes for the production of ribosomal RNA by transcribing a large (45S) precursor molecule

Question 14

How are ribosomes formed?

Answer 14

The nucleolar organiser DNA codes for production of rRNA by transcribing a large (45S) precursor molecule. Then the ribosomal proteins (found in cytoplasm) combine with the 45S precursor to make a 80S pre-ribosomal particle. Which then breaks down into the 40S and 60S subunits

Question 15

What are the 3 pockets that are in the ribosomal structure called?

Answer 15

1. A-site (Aminoacyl-tRNA binding site)
2. P-site (Peptidyl-tRNA binding site)
3. E-site (exit site for the tRNA after it drops off the amino acids. Goes back into the cytoplasm to get more)

Question 16

What are the two distinct populations of ribosomes?

Answer 16

• Bound ribosomes on the membranes of the rough ER

- Free ribosomes in the cytoplasmic matrix

Question 17

Polysomes?

Answer 17

The functional unit of protein synthesis of the ribosome. 5-20 ribosomes bound by a mRNA strand.

Either:
Bound polysomes- transfer proteins into the cisterna of the rough ER
Free polysomes- release their proteins into the cytoplasmic matrix

Question 18

How do antibiotics typically work?

Answer 18

• originate from bacteria and fungi
• many antibiotics have particular characteristics that allow them to target the site of infection
• Work via selective toxicity: through interference with biological structure or processes common to bacteria, but not humans. I.e. targeting bacterial ribosomes so the infection can’t grow bc the ribosomes can’t make proteins

Question 19

Free polysome function?

Answer 19

Release their proteins into the cytoplasmic matrix

Question 20

Bound polysome function?

Answer 20

Transfer proteins into the cisterna of the rough ER

Question 21

Proteins made on ribosomes may be further modified within what structure?

Answer 21

Golgi complex