Physiology 3140A Lecture Notes - Lecture 25: Endoplasmic Reticulum, Embryonic Stem Cell, Lamin B2
2 May 2018
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Cell Physiology Lecture 25
The Nucleus
November 22 2017
Structure of the nucleus
- Double plasma membrane
- Contains DNA;
o Heterochromatin: areas of gene silencing
▪ Tightly packed
▪ Hard for transcription machinery to get to the DNA – the DNA is often silenced
▪ DARKER AREA
o Euchromatin: areas of gene expression
▪ Not as tightly packed
▪ Transcription machinery can get to it
▪ LIGHTER AREA
- Nucleolus:
o Region for ribosome synthesis
o Involved in cell response to stress
o Assembly of signal recognition particles
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Nuclear envelope
- Made up of two phospholipid bilayers (outer and inner)
o Double membrane
o Continuous with the endoplasmic reticulum
- Has nuclear pores
- The outer is continuous with the endoplasmic reticulum
- Structural support on inner surface by the nuclear lamina
- How is this structure maintained?
o This is important – it helps keep the DNA organized
o Lamins!
▪ Structural support is from the inside of the
membrane and is formed by the nuclear
lamina
Nuclear Lamin
- Protein meshwork
- Mostly made up of lamins and lamin associated proteins
o Connect to the inner nuclear membrane
o Connect to chromatin (DNA in the nucleus)
▪ By keeping chromatin attached to nuclear lamina it keeps it organized in certain
positions + will be associated with microfilaments that extend up to the cellular
membrane, where it can be a response to signaling pathways
- Lamin associated proteins; LAP1, LAP2, Emirin
Lamins
- Type of intermediate filament found in the nucleus
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find more resources at oneclass.com
- A-type – all types encoded from alternate splicing of the LMNA gene
o All encoded from the same gene
o Alternative splicing of LMNA to create many different A type lamins
- B-type – encoded by two genes, LMNB1 & LMNB2
- A + B type lamin are found around the nuclear membrane
Lamin function
- A-type lamins higher expression in mechanical type tissues skeletal and cardiac muscle
o More sturdy
o Give nucleus a firm structure
- B-type function may be disposable but more highly expressed in undifferentiated cells (embryonic
stem cells)
o More flexible
o Undifferentiated cells need to get somewhere, they must be able to pass between cells –
want the nucleus to be flexible so it can move through tight spaces
- Structural support and shape to the nucleus
- Associate with chromosomes
o Helps in the signalling of transcription
o Coordination of cytoplasmic processes and divisions
o It helps keep the chromosomes organized during cell division
- Help with transport
o Nucleus is not always in the middle of the cell – it can be moving around
o Lamin and the LINC complex associate with the cytoskeleton and motor proteins to move the
nucleus around the cell
- Associated with mechanotransduction
o When the cell under goes mechanical stress – it signals to the nucleus directly and activate
transcription
- Regulate gene expression
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Involved in cell response to stress: assembly of signal recognition particles. Made up of two phospholipid bilayers (outer and inner: double membrane, continuous with the endoplasmic reticulum. The outer is continuous with the endoplasmic reticulum. Structural support on inner surface by the nuclear lamina. How is this structure maintained: this is important it helps keep the dna organized, lamins! Structural support is from the inside of the membrane and is formed by the nuclear lamina. Type of intermediate filament found in the nucleus. A-type all types encoded from alternate splicing of the lmna gene. B-type encoded by two genes, lmnb1 & lmnb2: all encoded from the same gene, alternative splicing of lmna to create many different a type lamins. A + b type lamin are found around the nuclear membrane. A-type lamins higher expression in mechanical type tissues skeletal and cardiac muscle: more sturdy, give nucleus a firm structure.
