Cell membrane and nucleus

Under the EM it is roughly 7.5-10nm for the plasma membrane

Fluid mosaic model is proposed by singer & nicolson (1972)

its for 2 dimesional liquid

consists of phospholipid, embedded with proteins, has a glycocalyx

Membrane Proteins
- Integral and peripheral membrane proteins play critical roles in cellular architecture and function
- Transmembrane Proteins: Cross the membrane entirely, with hydrophilic extracellular and intracellular domains, facilitating communication and transport across the membrane.
  - Signal Transduction: Binding with signal molecules such as hormones
  - cell recognition: they have identification tags like bacteria, antigens, cell recognizes
  - Intercellular junction: cell adhesion protiens attach membranes
- Peripheral Membrane Proteins: Attach to the surface of membranes, influencing intracellular signaling and structural integrity.
Semi-Permeable Membrane
- Acts as a barrier regulating the passage of substances between the internal environment of the cell and the external surroundings.
- Allows selective transport of molecules (e.g., essential proteins and ions) while maintaining the ability to sense and respond to external signals.
- Interaction sites between the cell's internal environment and its external surroundings are facilitated by membrane proteins, which can sense environmental changes.

Cell Nucleus
- Encases the cell's genetic material (DNA) and regulates cellular activities such as growth and metabolism.
- Site of transcription and RNA processing, playing a pivotal role in gene expression and the production of ribosomes.
DNA Structure
- DNA exists as a double helix composed of nucleotide pairs.
- During transcription, specific messenger RNAs are synthesized as needed by the cell.

Components
- Glycolipids and glycoproteins on the cell membrane have carbohydrate chains extending into the extracellular environment, forming the glycocalyx.
- This hydrated gel-like structure aids in cell-cell adhesion and recognition, contributing to tissue integrity and immune responses.

Role of Cholesterol
- Incorporation of cholesterol into the membrane modulates its fluidity, preventing it from becoming too fluid at high temperatures or too rigid at low temperatures.
- Maintains membrane integrity and optimum function.

Transport Proteins
- Essential for the movement of charged and large molecules across the membrane, especially against concentration gradients (e.g., sodium-potassium pump).
- Specific transmembrane channels allow ions to move according to their concentration gradients.
Integral Membrane Proteins
- Comprise various types, including those with multiple alpha helices that enable stable integration within the lipid bilayer.
- Form channels or act as receptors for signaling pathways.

Cell Surface Proteins
- Interactions with external signals trigger intracellular responses, influencing cytoskeletal changes and cellular behavior.
- Abnormal protein expression can trigger immune responses, aiding the identification of infected or cancerous cells by antigen recognition.

Types of Junctions
- A key type is the gap junction, consisting of proteins that facilitate communication between adjacent cells.
- They link the cytoplasm of neighboring cells, playing a role in tissue homeostasis.

Bacterial Cell Structure
- Bacteria typically have a single, circular chromosome situated in the cytoplasm with no nuclear envelope.
- Limited capability for RNA synthesis compared to eukaryotic cells, which compartmentalize various processes within a well-defined nucleus.

Nuclear Envelope
- Consists of two membranes, with nuclear pores regulating the passage of materials in and out (size-dependent).
- Chromatin is composed of DNA wrapped around histone proteins, leading to compact organization necessary for cellular function.
Histone Interaction
- DNA is compacted into structural units through wrapping around histones, forming solenoids and further looping to achieve a highly organized structure appropriate for cell division and gene regulation.