Nucleus,Ribosomes,Proteosomes,Peroxisomes

Question 1

What are the two critical functions of the nucleus?

Answer 1

1.Contain and protect DNA
2.Coordinates cellular activity

N.B:
8-10% of cell volume, and absent in RBCs

Question 2

What are the main components of the nucleus?

Answer 2

1.Lamina
2.ER
3.INM
4.ONM
5.Chromatin
6.Nuclear pore complex

Question 3

What does the inner/outer nuclear membrane do?

Answer 3

INM-Binds to chromosomes and has anchors for nuclear lamina

ONM-Continuous with ER and plastered with pores and ribosomes

In between is Perinuclear space

Question 4

What do network of laminate (intermediate filaments) do in nucleus?

Answer 4

Cohesion of nuclear envelope and also can disappear in mitosis if envelope breaks down

Question 5

Describe the nuclear pore complex and its abundance per cell?

Answer 5

30 types of nucleoporins 400-2000 per cell

Central water filled channel
8 filaments project into cytoplasm and another 8 project into nucleoplasm (this one is joined to form a nuclear basket

Question 6

Name two types of nucleoplasmic transport in detail

Answer 6

Passive transport which is bidirectional for water, ions, proteins etc

Active transport used for signal sequences:
-Nuclear localisation signal (NLS bond to importin)
-Nuclear export Signal (NES bond to exportin)

Question 7

Name two function units of the nucleus

Answer 7

Chromatin and the nucleolus

Question 8

What is chromatin?

Answer 8

DNA and histones
Which are visible as chromosomes during cell division

Question 9

Describe the Nucleolus

Answer 9

Non membranous organelle within nucleus

-contains genes encoding for rRNA and place for synthesis of rRNA and assembly of ribosomes

Question 10

What does the small and large unit of the ribosome do?

Answer 10

Small unit matches tRNA anticodons with mRNA codons

Large unit catalyses formation of peptide bonds

Question 11

What subunit numbers add up to get prokaryotic and eukaryotic ribosomes?

Answer 11

Prokaryotic ribosomes - 50s+30s=70s

Eukaryotic ribosomes - 60s+50s=80s

S=svedberg units of sedimentation

Question 12

Some facts about ribosomal RNA

Answer 12

2/3rds of ribosome composed of rRNA
Proteins serve to fold and stabilise rRNA

catalytic site composed of rRNA (ribozyme is ribosome)

Question 13

Describe the proteasome

Answer 13

Not membrane bound and large macromolecular complex

Functions to degrade unwanted protein in cytosol

Question 14

Describe the structure of peroxisome

Answer 14

Membrane bound spherical organelle which is rich in enzymes like OXIdases

Lipid bilayer and oxidase crystalline core

Question 15

What are the functions of peroxisome

Answer 15

-Oxidative breakdown of FA,AA, and toxins such as uric acid
-They yield H2O2 and contain catalase to break that down into water and oxygen
-Site for synthesis of cholesterol and other metabolites for biosynthetic pathways
-in liver cells they produce bile acids