A2.2.6 - Cell Structure

What are the universal organelles

ribosomes, cytoskeleton, plasma membrane

what are the Eukaryotic only organelles

Nucleus, endoplasmic reticulum, Golgi Apparatus, Mitochondrion, Peroxisome, Centrosome

what are the plant only organelles

chloroplast, vacuole, cell wall

what are the animal cell only organelles

lysosome

what is the structure and function of

nucleus

Structure:

• Double membrane (nuclear envelop) structure embedded with pores

• contains an inner region called a nucleolus

• Contains linear chromosomes made of DNA associated with proteins.

Function:

• Stores genetic material (DNA) as chromatin contained within gel-like solution (nucleoplasm)

• nucleolus is site of ribosome assembly

• Control centre → Controls gene expression: regulates which genes are turned on or off

• Nuclear pores allow substances such as mRNA to move between nucleus and cytoplasm.

what is the structure and function of Mitochondrion

Structure:

• Double membrane.

• Smooth outer membrane.

• Inner membrane folded into cristae.

• Interior is the matrix.

• Matrix contains enzymes, circular DNA and 70S ribosomes.

• Intermembrane space lies between the two membranes.

Function:

• Site of aerobic respiration.

• Produces ATP through oxidative phosphorylation.

Adaptations of the mitochondrion

Adaptations

Cristae

→ Increase surface area

→ More ETC proteins + ATP synthase

→ Greater capacity for ATP production.

Intermembrane space

→ Small volume

→ H⁺ ions accumulate quickly

→ Creates a steep proton gradient.

Matrix

→ Contains enzymes for the link reaction and Krebs cycle.

what is the structure and function of ribosomes

Structure:

• Two subunits made of RNA and protein

• larger in eukaryotes (80S) than prokaryotes (70S)

• Can be free in the cytoplasm or attached to rough ER.

Function: Site of translation/protein synthesis.

• Free ribosomes: make proteins used mainly inside the cell.

• Rough ER ribosomes: make proteins destined for secretion, membranes or lysosomes.

Free vs Bound Ribosomes

Free ribosomes
→ Proteins used mainly within the cell.

Ribosomes attached to RER
→ Proteins for secretion, membranes or lysosomes.

what is the structure and function of

Endoplasmic Reticulum

Structure:

• A network of membrane bound tubules and flattened discs (cisternae)

• may be bare (smooth ER) or studded with ribosomes (rough ER)

• Rough ER: Continuous with the nuclear envelope.

• Smooth ER: continuous extension of the rough ER

Function: Synthesize and transport lipids (Smooth ER) and proteins (rough ER)

what is the structure and function of Golgi Apparatus

Structure:

• Stack of flattened, membrane-bound sacs called cisternae

• Cis face: Points towards ER, receives transport vesicles

• Trans face: Points towards cell membrane and sends products to final spots in/out cell

Function:

• Modifies, sorts and packages proteins and lipids.

• Produces vesicles for transport/secretion.

• Helps form lysosomes.

Structure + function of vesicles

Structure:

• Small spherical membrane-bound sacs

• Surrounded by a phospholipid bilayer.

• Can bud off from or fuse with cell membranes/organelles.

Function:

• Transport substances between organelles.

• Transport materials to the plasma membrane for secretion.

• Can carry digestive enzymes in lysosomes.

Endocytosis

Uptake of substances into the cell by the plasma membrane forming a vesicle.
Membrane folds inward → surrounds substance → pinches off → vesicle forms.

Phagocytosis: Endocytosis of large particles/cells
Pinocytosis: Endocytosis of fluid and dissolved substances

Exocytosis

Release of substances out of the cell when a vesicle fuses with the plasma membrane.
Vesicle moves to membrane → fuses with membrane → contents released outside.

What is the endomembrane system pathaway

Nucleus → RER → transport vesicle → Golgi apparatus → vesicle → destination

Endomembrane system process for secreted protein

DNA → mRNA → ribosome on RER → protein → vesicle → Golgi → secretory vesicle → plasma membrane → outside cell

Similarity of endocytosis and exocytosis

Both use vesicles and require ATP

what is the structure and function of lysosome

Structure: Membranous sacs filled with hydrolytic enzymes with acidic internal environment

Function: Breakdown / hydrolysis of macromolecules (presence in plant cells is subject to debate)

what is the structure and function of Peroxisome

Structure: Membranous sac containing a variety of catabolic enzymes

Function: Catalyses breakdown of toxic substances (e.g. H2O2) and other metabolites

what is the structure and function of Centrosome

Structure: Microtubule organising centre (contains paired centrioles in animal cells but not plant cells)

Function: Radiating microtubules form spindle fibres and contribute to cell division (mitosis / meiosis)

what is the structure and function of Centriole

Structure:

• Cylindrical structures made of microtubules.

• Each centriole contains nine sets of microtubule triplets arranged in a ring.

• Found in animal cells and some other eukaryotic cells.

Function:

• Organize microtubules.

• Help form the spindle during cell division.

what is the structure and function of Chloroplast

Structure:

• Double membrane structure with internal stacks of membranous discs (thylakoids)

  • Contain chlorophyll, electron carriers and ATP synthase.

  • Site of light-dependent reactions.

• Thylakoids are arranged into stacks called grana. → large surface area

• Grana are connected by intergranal lamellae.

• Fluid surrounding thylakoids = stroma.

• Contains chlorophyll, circular DNA and 70S ribosomes.

Function:

• Site of photosynthesis

• Converts light energy into chemical energy, stored as glucose

what is the structure and function of vacuole

Structure:  

• Fluid-filled internal cavity surrounded by a membrane (tonoplast)

• Contains cell sap

Function:  

• Maintains turgor pressure.

• Helps support the plant cell.

• Stores substances such as ions, sugars and pigments.

what is the structure and function of cell wall

Structure: External outer covering made of cellulose

Function:

• Provides mechanical support.

• Maintains cell shape.

• Prevents cells from bursting when water enters.

Structure + function of cilia

Structure:

Short, numerous hair-like extensions

Core axoneme 9+2 microtubule arrangement

Function:

move substances across cell surface

Structure + function of microtubules

Structure

• Cylindrical structures

• Made of 9 triplets of microtubules

Function

• provide structural support

• act as tracks for intracellular transport

• Form spindle fibres for cell divison

Structure + function of cilia

Structure:

• Short numerous hair-like extensions

• Core (axoneme) has 9+2 microtubule arrangement

Function:

• Beat in coordinated wave to move substances across cell surface

flagellum structure and function

Structure:

• Long whip-like extensions surrounded by plasma membrane

• Core structure (axoneme)

  • 9 outer pairs of microtubules

  • 2 central single microtubules

Function

• Whip back and forth to propel cell

what is the structure and function of

Plasma membrane

Structure:

• Phospholipid bilayer embedded with proteins

• Contains cholesterol and carbohydrate chains

• Fluid and selectively permeable.

Function:

• Controls movement of substances in and out cell

• Allows cell signalling and communication.

• Maintains the cell's internal environment.

Structure + function of cytoplasm

Structure:

• Jelly-like region inside the plasma membrane.

• Contains the organelles.

• Includes the cytosol.

Function:

• Site of many metabolic reactions.

• Allows substances to move around the cell.

Structure + function of cytoskeleton

Structure:

• Filamentous scaffolding within cytoplasm

• Made of protein fibres: microtubules, microfilament

Function:

• Provides internal structure

• Helps move organelles and vesicles.

• Microtubules form the spindle during cell division.