Cellorganeller och cytoskelett

What is the endoplastic reticulum? (ER) Describe the different parts and how it’s connected to other parts of the cell.

Organelle directly connected to the nuclear envelope. Has a rough and smooth part. Connects to the golgi aparatus. Proteins and lipids from the ER are packaged into vesicles that travel to the Golgi apparatus for further modification, sorting, and transport.

The rough ER is where the ribosomes attach and create proteins.

The smooth ER is where lipids are created. SER can be found mainly in liver and gonad cells (könsceller). Involved in lipid synthesis, steroid hormone production, detoxification (e.g., liver), and calcium storage (especially in muscle cells).

Name the differences between plant cells and animal cells.

Plant cells have rigid cell walls.
Plant cells have chloroplasts that contains chlorophyll, needed for photosynthesis.
Plant cells has a large vacuole (stores water, nutrients etc)
Plant cells are regular in shape, this is not the case for animal cells.

Name the similarities between plant cells and animal cells.

Both have a nucleus, nuclear envelope and chromosomes that carry DNA.
Both have cytoplasm.
Both have mitochondria.
Both have cell membranes.

What is the endomembrane systems?

Organelles that exchange materials through vesicles, contains the nucleus, endoplasmic reticulum, Golgi apparatus, vesicles, lysosomes, endosomes, vacuole, plasma membrane.

Which organelles are energy-producing in a cell?

Mitochondria and chloroplasts.

Which organelles are associated with the cytoskeleton?

Microtubules and actin. Set of components that shape and give mechanical resistance to the cell

Name the parts of the nucleus and their functions.

Nucleolus: Creates rRNA (creates ribosomes)

Chromatin: DNA and protein (8 histones and 146 bp DNA, forms nucleosomes that can then be packed into chromosomes).

Nuclear envelope: inner and outer membrane.

Pores: in the nuclear membranes allow for transport of ribosomes to the ER.

Endoplastic reticulum: Extension of the outer membrane, site for creation of proteins by the ribosomes and lipids etc.

Describe the function of the Golgi apparatus and it’s parts.

The Golgi apparatus is where materials synthesized by the cell in the ER gets received. It’s made up of flat membrane sacks called cisternae and has a cis-side (recieving) and a trans side (shipping side).

It recieves vesicles from ER with newly created proteins. It modifies some of the proteins recieved from the ER. Sends vesicles to endosomes, lysosomes and plasma-membrane secretion.

Explain vesicles and their functions.

A vesicle is a type of small vessel which is used to transport material around the cell. They can transport materials in the cell or outside of the cell in a process called exocytosis.

what are lysosomes and endosomes?

Lysosomes: Membrane bound organelles that contain hydrolytic enzymes that break down old or damaged organelles, Food particles, Pathogens (like bacteria). Works as the cells digestive system. Also works with cell recycling (autophagy).

Endosomes: Membrane bound compartments that aid the cell in sorting, and transporting internilized materials. They are formed through endocytosis and either transport materials to lysosomes for degradation or recycle the material to be used in the plasma membrane again.

What are vacuoles?

Exists in plant cells and help maintain turgor (the structure of the plant cell). Functions as reservoirs for water nutrients and ions for the cell. Crucial to processes of detoxification and general cell homeostasis

Homeostasis = the process by which a living organism maintains a stable internal environment, despite changes in the external environment.

Explain endocytosis.

Endocytosis is the process of something extracellular getting transported into the cell. A molecule or something else connects to the plasma membrane and gets engulfed by it and forms a vesicle.

In short: vesicle → early endosome → late endosome → lysosome = the cell’s import, sorting, and digestion pathway.

How many types of endocytosis is there? What are they?

Three.

Phagocytosis (“cell eating”) – large particles, like bacteria, are engulfed into phagosomes.

Pinocytosis (“cell drinking”) – small droplets of fluid are taken in.

Receptor-mediated endocytosis – specific molecules bind to receptors on the cell surface before being internalized.

Explain exocytosis.

The cell exports materials out of the cell through vesicles. Vesicles containing proteins, waste, or signaling molecules fuse with the plasma membrane. Their contents are released into the extracellular space.

Important for:

Secretion of hormones or neurotransmitters

Delivery of membrane proteins or lipids

Removing waste products

What is a proteasome?

Degradation protein-complex in the cytoplasm and nucleus. It degrades proteins marked with ubiquitin.

What happens in the cytoplasm?

Key things that happen there:

• Translation – ribosomes synthesize proteins from mRNA.

• Glycolysis – breakdown of glucose for energy.

• Metabolic reactions – synthesis and breakdown of molecules.

• Signal transduction – molecules transmit signals within the cell.

• Transport of vesicles and organelles – cytoskeleton helps move things around.

In short: cytoplasm = the cell’s workspace where metabolism and protein synthesis mostly occur.

Explain the cytoskeleton.

Network of protein filaments that extend throughout the cell. Consists of microtubules, actin filaments and intermediate filaments.

What are actin filaments?

Double stranded helix actin. Thin, flexible proteinfibers that help support the shape, movement and transport in the cell.

What are intermediate filaments?

rope-like fiber filament proteins. Maintain cell shape and organize 3D structure of the cell

What are micorubules?

Hollow cylinders made up of alfa and beta tubulin dimers. Maintain cell shape and resist compression.

• Intracellular transport – motor proteins (kinesin, dynein) move vesicles and organelles along them.

• Cell division – form the mitotic spindle that separates chromosomes.

• Cilia and flagella – core structure for cell movement or fluid movement across cell surfaces.

Explain MTOC (Micortubule organizing center)

MTOC (Microtubule Organizing Center) = a cellular structure where microtubules are nucleated and organized.

• In most animal cells, the main MTOC is the centrosome, located near the nucleus.

• Composed of two centrioles surrounded by pericentriolar material (PCM).

• Functions:

  • Initiates microtubule growth (minus ends anchored at MTOC, plus ends grow outward).

  • Organizes the cytoskeleton for shape and intracellular transport.

  • Forms the mitotic spindle during cell division to separate chromosomes.

In short: MTOC = the cell’s microtubule “headquarters” for growth, organization, and division.