Topic B: Cell Biology (Cell Organelles)

Outline the cell theory.

• The cell theory states that all cells come from pre-existing cells, cells are the smallest unit of life, and that all organisms are composed of cells. 

Outline the structure and function of the rough endoplasmic reticulum.

• Ribosomes bound to the rER are responsible for synthesizing proteins which will be used within the cell. 

• The rER is responsible for assisting newly synthesized proteins to fold into their unique three dimensional conformational shape. 

• Transport vesicles containing newly synthesized proteins will bud off the rER and travel towards the Golgi appartus for chemical modifications. 

• Glycosylates proteins by adding a short carbohydrate chain to the end of the protein.

Structure:

• Three dimensional network consisting of interconnecting flattened membrane bound sacs (FIMBS) called cisternae.

• Single membrane.

• Ribosomes attached to cytoplasmic side. 

• Continuous with outer nuclear membrane.

Outline the role and structure of the smooth endoplasmic reticulum.

• Involved in detoxification processes.

• Synthesis of lipids such as phospholipids and cholesterol.

Structure:

• Single membrane

• Made up of a three dimensional flat, interconnected membrane bound sacs called cisternae.

Outline the role and structure of the Golgi apparatus. 

• Chemical Modification + Storing: Transport vesicles containing proteins will bud off the rER and travel towards the Golgi Apparatus, before fusing with the cis face of the Golgi Apparatus, and releasing its contents into the Golgi apparatus. Within the GA, proteins will stored and concentrated and then be chemically modified (ie: glycosylation or phosphorylation) before being repackaged into secretory vesicles that will then bud off the trans face of the Golgi apparatus, and travel along cytoskeletons to their target destination.

• Formation of Lysosome Enzymes.

Structure:

• Single membrane.

• Made up of a stack of flattened membrane bound sacs called cisternae. (NON-INTERCONNECTING)

Outline the role and structure of the mitochondria

• Site of cellular respiration.

• Site of synthesis of mitochondrial proteins.

Structure:

• Double membrane

• Cylindrical shaped

• Consists of extensively folded cristae that gives rise to large surface area to allow for many electron carrier proteins, as well as stalked particles containing ATP synthase to be embedded, thereby maximising the rates of photosynthesis.

• Consists of mitochondrial matrix that contains mitochondrial DNA, enzymes of Link Reaction and Krebs cycle, glycogen granules and 70S ribosomes.

Outline the role and structure of the ribosomes.

• Site of protein synthesis. Free ribosomes will synthesize proteins that are meant to be used out of the cell, while bound ribosomes on the rER will synthesize proteins meant to be used in the cell.

Structure:

• Spherical

• Non membrane bound

• Consists of a large ribosomal subunit and a small ribosomal subunit.

• Each subunit is made up of rRNA and ribosomal proteins.

Outline the role and function of the lysosomes.

• Degradation of unwanted organelles (autophagy).

• Digestion of foreign particles via phagocytosis. Fuses with the membrane of phagosome, and hydrologic enzymes will then degrade and digest the substances into smaller soluble products.

Structure:

• Small, spherical

Outline the role and structure of the chloroplasts.

• Site of photosynthesis within plants.

• Site of chloroplast protein synthesis.

Structure:

• Double membrane

• Consists of stroma which contains 70S ribosomes, enzymes involved in Calvin cycle, starch grains and circular DNA.

• Has an extensively folded inner surface that gives rise to thylakoids and lamellae. Thylakoids are stacked in order to form grana which increases the surface area to allow for more embedding of electron carriers and stalked particles containing ATP synthase, as well as photosystems containing chlorophyll.

Outline the role and structure of the cell surface membrane. 

Outline the role and function of the nuclear envelope.

• Double membrane.

• Contains pores in the nuclear envelope to allow for the entry and exit of small molecules, such as the exit of mRNA into the cytoplasm

Outline the role and function of the centrioles. 

• Pair of rod like structures which are arranged perpendicular to one another.

• Composed of nine sets of triple microtubules arranged in a ring.

Function:

• Involved in the organisation of microtubules into spindle fibres during cell division.

• Will replicate during cell division.

Outline the role and structure of the nucleus. 

• Contains hereditary material (DNA) which will be passed on from parents to offspring.

• Site of DNA replication.

• Directs protein synthesis.

• Consists of nucleolus, which is the site of rRNA synthesis. Ribosomal proteins, alongside rRNA will be assembled to form large and small ribosomal subunits which will then exit via nuclear envelope into cytoplasm to be assembled into proteins.

Structure:

• Spherical

• Made up of double membrane outer nuclear envelope which has the presence of nuclear pores.

• Contains of DNA in the form of chromatin (when not dividing). Euchromatin is less condensed form of DNA that is highly transcribed while heteronormative contains of highly condensed form of DNA that is less frequently transcribed.

• Also consists of nucleolus.

Outline the role and function of the nucleolus.

• Site of rRNA synthesis. Within the nucleolus, ribosomal proteins alongside rRNA will be assembled to form large and small ribosomal proteins. The small and large ribosomal proteins will then exit via nuclear pores and travel towards the cytoplasm, where they will be assembled into a ribosome,