Lecture 16: Role Of The Nucleus And Into To DNA

Question 1

Nuclear structure:

Answer 1

Nuclear membrane: double membrane separated by inner-nuclear space, and is contiguous with rough endoplasmic reticulum
Nuclear pores: double membranes fuse together at points, forming these pores. They are sites which allow for transport into and out of cell
Nucleolus: dense, non membranous sub-organelle
-site if RNA synthesis
-contains genes coding for rRNA
Euchromatin: unconcerned chromatin that stains poorly
-constitutes DNA that is being actively transcribed
Heterochromatin:
-heterochromatin condensed chromatin that stains well
-associated with nuclear envelope and nucleolus
-some heterochromatin always remains packed, whole other forms can be activated in specialised tissues.
Nucleoplasm: matrix of the nucleus (like cytoplasm of cell)
-contains enzymes, hormone receptors, precursors

Question 1

Nuclear composition. What are the major components?

Answer 1

1. Protein: (75-80%)
   Two types of nuclear proteins
   A) Histones (basic proteins)
   -involved as structural proteins with chromosomes
   B) Non-histone chromosomal proteins
   -include various enzymes and hormone receptors
   -considered to play a regulatory role
2. DNA -15%
   -represents bulk of cellular DNA
   -small amount found in mitochondria and chloroplasts (plants only)
3. RNA -5-10%

Question 3

Describe how chromosomes are formed

Answer 3

Short region of DNA double helix, they surround proteins like beads on a string called chromatin, lots of chromatin condense together to form nucleosomes, which becomes a condensed section of chromosomes, then forms the entire mitosis chromosome. Refer to page 5 for picture

Question 4

What does the nucleus do?

Answer 4

The control centre of the cell

• it contains the cells genetic information
• this genetic information directs the overall function of the cell

Question 5

What is the evidence that we have to show the nucleus is the control centre of the cell?

Answer 5

1. Micro manipulation with amoeba:
   - remove nucleus with fine needle
   - amoeba stays alive for some time
   - but rounds up and stops moving
   - proteins synthesis stops
   - nucleus is replaced with one from another amoeba and process is reveresed back to normal activity.
2. Hammerlings experiments with acetabularia
   - a single cellos algae consists of a rhizoid (region with nucleus) and stalk
   - when sectioned, only the rhizoid section is able to regenerate a complete algae

Question 6

What substance carries the genetic information?

Answer 6

The nucleus is not what constitutes the hereditary material
-remember that prokaryotes have NO nucleus
So what is the chemical that carries the genetic info?

Question 7

Why was proteins believed to be the hereditary material?

Answer 7

Proteins was viewed as more complex (20 amino acids) than the ‘simple reading polymer’ of DNA.
Obviously this isn’t the case

Question 8

Evidence for DNA as genetic material

1. Bacterial transformation

Answer 8

1. Bacterial transformation:
   We had one penicillin-resistant strain of bacterium X (able to produce an enzyme that breaks down penicillin and is therefore resistant to penicillin. And the other is penicillin sensitive strain of bacterium (doesn’t produce the enzyme and is killed by penicillin)

When DNA from penicillin-resistant bacteria is added to cells of the sensitive strain- some of the sensitive cells take up the DNA and gain ability to produce the enzyme which breaks down penicillin.

Question 9

Evidence for DNA as genetic material

2. Viruses contain DNA

Answer 9

The Hershey-chase experiment:

• investigated the infection of bacteria by a bacterial virus
• viruses consist of DNA and protein
• using an example of one set of DNA and protein it was established that on infection only the DNA gains entry into the host cell.
• yet this contains enough information to code for a large number of new viral particles (DNA is the important info centre woo)