Lecture 9

Question 1

What is a ribosome? Where are they found and what do they do?

Answer 1

Ribosomes are complexes made of ribosomal RNA, and are synthesized in the nucleus. They are found as free ribosomes in the cytoplasm, and bound ribosomes on the rER. They carry out the translation of RNA.

Question 2

What is the nucleus structure?

Answer 2

• surrounded by nuclear envelope
• has channels called nuclear pores
• contains tightly packed DNA
• has prominent area called nucleolus

Question 3

What is the structure of the nuclear envelope?

Answer 3

• 2 membranes made of phospholipid bilayer
• outside and inside membranes have perinuclear space between
• outer membrane is continuous with ER

Question 4

What is the nuclear lamina? What does it do?

Answer 4

• the inner surface of the nuclear envelope
• composed of intermediate filaments
• maintains shape of nucleus
• helps organise the packing of DNA within the nucleus

Question 5

What are nuclear pores and what do they do?

Answer 5

• channels made of nuclear proteins (nucleoporins) that form nuclear pore complex
• controls the movement of molecules in and out of the nucleus

Question 6

What substances leave the nucleus to the cytoplasm?

Answer 6

• mRNA
• tRNA
• ribosomal subunits

Question 7

What substances go from the cytoplasm to the nucleus?

Answer 7

• control signals
• building materials
• ATP

Question 8

What is the nucleolus and what does it do?

Answer 8

• non-membrane bound structure within nucleus
• there are multiple in the nucleus
• it is responsible for making ribosomal RNA and ribosomal subunits

Question 9

How is DNA organised in the nucleus?

Answer 9

DNA double helix (2 nanometres wide) –> interacts with histone H2-H4 (type of protein) –> folds DNA into ‘beads’ called nucleosomes (10 nanometres wide) –> then interacts with histone 1 (H1), causing it to coil (30 nm wide) –> loops to form 300nm wide fibre –> during cell division the 300nm fibres coil to form metaphase chromosomes

Question 10

What is euchromatin and heterochromatin?

Answer 10

Euchromatin = less electron opaque, contains genes being used by the cell
Heterochromatin = more electron opaque, contains genes not being used by the cell as not enough room for transcription to occur
Euchromatin + heterochromatin are dynamic