Cell Bio Lecture 1: Nucleus Structure and Function Flashcards
(14 cards)
Describe the nuclear envelope.
Made up of two membranes. Surrounds the nucleus in a cell in interphase.
Outline the differences between the two nuclear membranes.
Outer: has ribosomes attached and is continuous with smooth and rough ER.
Inner: Associated with fibrous lamina (nuclear lamina)
What is the nuclear lamina?
A 50nm thick layer of fibrous proteins (nuclear lamins) on the inside of the nucleus that give structural stability, provide an anchor for pores and chromatin, and regulate assembly/disassembly of envelope during mitosis. Looks like a mesh under electron microscopy.
What is Progeria?
A disorder caused by a point mutation, progeria results in an unusable protein lamin A. The lamina does not form properly and results in accelerated aging and death occurs in teenage years.
What is restrictive dermopathy?
Rare, lethal, autosomal recessive disorder caused by loss of a gene that allows for cleavage of a pre-lamina into a mature nuclear lamina. Without the mature nuclear lamina the skin is not able to grow in the fetus and the fetus suffocates.
Describe the nuclear matrix.
A complex of fibrillar proteins inside the nucleus which can be the site of RNA processing.
Define chromatin.
Highly condensed nuclear DNA complexed with histones and non-histone proteins.
What are the two stages of chromatin and their corresponding characteristics?
- Heterochromatin: tightly wound, transcriptionally inactive.
- Euchromatin: diffuse, active transcriptionally.
What is a NLS and what is it involved in?
NLS stands for Nuclear Localization Signal. These are short (5 AA?) basic amino acid sequences in proteins destined for the nucleus, which are then recognized by importin (a protein on the nuclear pore), allowing the protein’s entry into the nucleus.
Describe the defect in nuclear transport in patients with Huntington’s Disease.
A protein called “huntingtin” aquired a NLS (or NLS-like properties) that causes it to be imported to the nucleus of brain cells. The amount of huntingtin in the nucleus is proportional to the severity of the disease.
What is the Golden Fleece Award?
Given by Senator William Proxmire (up til he retired in 1988) to the department deemed most wasteful. Often given to scientific researchers.
Is energy required for nuclear transport through a pore?
Yes, ATP is needed to cause the comformational change in the pore.
Name the protein on the nuclear pore that recognizes the NLS.
Importin.
Describe the process of lamins and phosphorylation in the nuclear envelope assembly/disassembly process.
In interphase, lamins are underphosphorylated and, in this state, hold chromatin to the nuclear lamina.
At the start of mitosis lamins are phosphorylated by kinase, causing them to release chromatin from the nuclear lamina. Chromatin begins to condense, and the nuclear membrane breaks up.
Late in mitosis phosphatase dephosphorylates the lamins and reassembly begins.
