The ultra structure of eukaryotic cells membrane bound organelles

What do eukaryotic cells have?

-nucleus surrounded by nuclear envelope DNA wound into linear chromosomes
-Jelly like cytoplasm
-area inside nucleus called nucleolus containing RNA( also involved in making ribosomes)
-cytoskeleton
- plasma membrane
- membrane bound organelles (other than nucleus mitochondria golgi apparatus endoplasmic reticulum)
- small vesicles
- ribosomes

Nucleus, nuclear envelope and nucleolus function(detail)

-Nuclear envelope separates contents of the nucleus from rest of cell
- some regions outer and inner nuclear membrane fuse together at these points some dissolved substances and ribosomes pass through
- pores enable larger substances such as mRNA to leave nucleus substances such as steroid hormones may enter nucleus from cytoplasm via pores
- nucleolus is where ribosomes are made
-chromosomes contain organisms genes

Nucleus, nuclear envelope and nucleolus structure

Nucleus surrounded by double membrane nuclear envelope with pores
- nucleolus has no membrane it contains RNA
- chromatin consists of DNA wound around histones
-when cell not dividing chromatin is spread out or extended -when cell is about to divide chromatin condenses coils tightly into chromosomes.
-Chromosomes nearly make up all organisms genome

Nucleus nuclear envelope and nucleolus function simplified

-Control Center of cell
-stores organisms genome
-transmits genetic information
-provides instructions for protein synthesis

Rough endoplasmic reticulum structure

-System of membranes containing fluid filled cavities (cisternaes) with the nuclear membrane
- covered with ribosomes

Rough endoplasmic reticulum function

- Is the intracellular transport system
- Cisternae form channels for transporting substances from an area of a cell to another
- Provided a large SA for ribosomes to assemble amino acids into proteins.
- proteins then actively pass thru membrane into cisternae and are transported to the Golgi apparatus for modification+ packaging

Smooth endoplasmic reticulum structure

- System of membranes containing fluid-filled cavities (cisternae) that are continuous with the nuclear membrane
- No Ribosomes

Smooth endoplasmic reticulum function

- contains enzymes that catalyze reactions involved with lipid metabolism, such as:
*synthesis of cholesterol
* synthesis of lipids/ phospholipids needed by the cel
*synthesis of steroid hormones
- It is involved with absorption, synthesis and transport of lipids (from the gut)

Golgi apparatus Structure

- Consists of stack of membrane-bound flattened sacs
- Secretory vesicles bring materials to & from Golgi apparatus

Golgi apparatus Function

Proteins are modified by :
- adding sugar mols to make glycoproteins
- adding lipid mols to make lipoproteins
- being folded into their 3D shape
Proteins are packaged into vesicles that are pinched off and then:
- stored in the cell
- moved into the plasma membrane, either to be incorporated into plasma membrane or exported outside the cell

Mitochondria structure

-spherical, rod-shaped or branched (2-5 micrometres long)

-Surrounded by 2 membranes with fluid-filled space between then. inner one folded into cristae

-inside is the matrix, which has enzymes for respiration

Mitochondria function

- Site of ATP production during aer respiration
- Self-replicating so more made if cell's energyneeds to increase
- Abundant in cells where much metabolic activity takes place (e.g liver cells + synpases between neurones where neurotransmitters are synthesised and transmitted)

Chloroplasts Structure

- Large organelles (4-10 micrometres long)
- Found only in plant cells + some protoctists
- surrounded by a double membrane or envelope.
-Inner membrane is continuous with stacks or flattened membrane sacs called thylakoids (containing chlorophyll)
- Each stack or pile of thylakoids is called a grunam (or grana). Fluid filled matric is called the stroma
- Chloroplasts contain loops of DNA and starch grains

Chloroplasts Function

- Site of photosynthesis
- First stage when light energy is trapped by chlorophyll and used to make ATP occurs in grana. Water split to supply hydrogen ions
- Second stage when hydrogen reduces carbon dioxide using energy from ATP to make carbohydrates occurs in stroma.
- Chloroplasts abundant in leaf cells particularly palisade mesophyll layer

Vacuole Structure

Surrounded by a membrane called the tonoplast and contains fluid.

Vacuole function

- Only plant cells have a large permanent vacuole
- Filled with water+ solutes and maintains cell stability as when its full it pushed against the cell wall, making cell turgid
- If all the plant cells are turgid then this helps to support the plant esp in non-woody plants

Lysosomes Structure

- Small bags formed from Golgi apparatus, each surrounded by single membrane
- Contains powerful hydrolytic (digestive) enzymes
- Abundant in phagocytic cells such as neutrophils and macrophages that can ingest & digest invading pathogens such as bacteria

Lysosomes Function

- Keep powerful hyrdolytic enzymes sepereate from the rest of the cell
- Can engulf old cell organelles and foreign matter, digest them and return the digested components to the cell for reuse.

Cilia and Undulipodia Structure

-protrusions from cell surrounded by cell surface membrane
-contain microtubules
-formed from centrioles

Cilia and Undulipodia Function

- Epithelial cells lining airways have hundreds of cilia that beat and move band of mucus
- Nearly all cell types in body have one cilium that acts as antenna, contains receptors and allows cell to detect signals about its immediate environment
- Only type of human cell that has Undulipodium is spermatozoon, which enables spermatozoon to move

Ribosomes ( without membranes) Structure

- small spherical organelles ( about 20nm)
- made of RNA
- Made in nucleolus (as 2 seperate sub units) , which pass thru nuclear envelope into cell cytoplasm+ then combine
- Some remain free in cytoplasm and some attach to endoplasmic reticulum

Ribosomes ( without membranes) Function

- Bound to the exterior of RER and are mainly for synthesising proteins that'll be exported outside the cell.
- Ribosomes that are free in cytoplasm, either singly or in clusters are primarily the site of assembly of proteins that will be used inside cell

Centrioles ( without membranes) Function

- Before cell divided, spindle made of threads of tubulin formed from the centriole
- Chromosomes attach to middle part of spindle + motor proteins walk along tubulin threads, pulling chromosomes to opp ends of cell
-Involved in the formation of cilia and undulipodia
*Before cilia form, centrioles multiply + line up beneath cell surface membrane.
*Microtubules then sprout outwards from each centriole (forming a cilium or undulipodium)
Centrioles are usually absent from cells of (higher) plants but may be present in some unicellular green algae, such as Chlamydomonas.

Centrioles ( without membranes) Structure

- consists of 2 bundles of microtubules at right angles to eachother. Microtubules made of tubulin protein subunits+ arranged to form a cylinder

Cytoskeleton ( without membranes) Structure

Network of protein structure within cytoplasm
Consists of :
Rod-like microfilaments made of subunits of the protein actin; they are polymers of actin+ each microfilament is about 7nm in diameter
- Straight, cylindrical microtubules made of protein subunits (tubulin) about 18-30 nm diameter
- Cytoskeleton motor proteins (myosins, kinesins + dyneins) are molecular motors. Also enzymes and have a site that binds to and allows hydrolysis of ATP as energy source.

Cytoskeleton ( without membranes) Function

- Protein microfilaments within the cytoplasm give support+ mechanical strength, keep cell's shape stable + allows cell movement
- Microtubules also provide shape + support to cells, help substances+ organelles to move thru cytoplams within a cell
*They form a track along with motor proteins (dynein and kinesein) walk + drug organelles from one part of cell to another
* Form the spindle before cell divides. Spindle threads enable chromosomes to be moved with the cell.
*Microtubules also make up cilia, undulipodia + centrioles. Intermediate fCellilaments are made up of a variety of proteins. They :
- anchor nucleus within the cytoplasm
- Extend between cells in some tissues(between special junctions) enabling cell-cell signalling + allowing cells to adhere to a basement membrane (therefore stabilising tissues)

Cellulose Cell wall Structure

- Cell wall of plants is on outside of plasma membrane
- Made from bundles of cellulose fibres

Cellulose cell wall Function

- Absent from animal cells, cell wall is strong and prevent plant cells from busting when turgid
- Provides strength + support
- Maintains cells shape
- Contribute to strengths and support of whole plant
- Permeable + allow solutions (solute and solvent) to pass thru
- Fungi have cell walls that contain chitin