biology mod 1

Preliminary Biology

Ellaha jafari

Module 1: Cells as the Basis of Life

Chapter 2: Cell Structure and Technologies

2.4 Organelles in Cells

Eukaryotic cells

All eukaryotic cells contain membrane-bound internal structures called organelles, each with a specific structure and function.

Membranes may be either double or single in structure.

Membrane- selective boundaries

Controls passage of water and other substances in and out of the cell.

Permits the passage of only certain molecules (selectively permeable), formed by the phospholipid bilayer.

Protoplasm- nucleus and cytoplasm

Nucleus + Cytoplasm (90% water)

Function: making cellular products and respiration

The cytoplasm consists of a liquid called the cytosol, which contains dissolved chemical substances (ions, such as chloride or sodium), suspended organelles and insoluble granules.

Nucleus- the control and information centre

Nucleus stores the information needed to control all cell activities.

Nucleus is surrounded by a double nuclear membrane or nuclear envelope, pierced by tiny pores called nuclear pore.

Pores regulate passage of substances between nucleus and cytoplasm, and allows communication between them.

Endoplasmic reticulum- transporting and processing of proteins and lipids

Provides a connection of pathways between nucleus and cell’s environment, allowing intracellular transport.

Rough endoplasmic reticulum (RER) has ribosomes attached.

Smooth endoplasmic reticulum (SER) doesn’t have ribosomes attached.

Main function is transport, but it also plays a role in the processing of cell products.

RER folds and processes proteins coded by the ribosomes. Can also synthesise lipids.

SER is the main site for lipid production, used in membrane repair and manufacture.

In plant cells, ER does intercellular transportation of substances, through channels (called cell pits) in the cell wall.

Ribosomes- protein synthesis

Small size increases surface area.

Made up of chemicals RNA and proteins.

They carry out genetically coded instructions of DNA to produce any proteins.

Amino acids are joined to form polypeptides.

Can be found free in the cytoplasm or scattered over the surface of ER.

Golgi bodies- packaging and sorting the products

Made of flat membranes, but unlike RER, it doesn't have ribosomes attached to it.

Golgi bodies process, package and sort cell products, such as polypeptides.

They add proteins and carbohydrates to cell products.

Membranes provided by Golgi are different and serve as a ‘packaging label’, sorting whether the cell product goes in or out of the cell via the transport vesicle.

Lysosomes- digestion and destruction

Organelles within the cytoplasm of cells reach their ‘best-before’ date.

Lysosomes are formed by the Golgi body.

They contain digestive enzymes that are responsible for splitting complex compounds into simpler ones.

Apoptosis- programmed cell death

Mitochondria- cellular respiration

Produces energy in the form of energy-rich molecules (cellular respiration)

Number of mitochondria in a cell depends on how much energy the cell needs to carry out its functions.

Energy chemical is ATP (adenosine triphosphate).

Mitochondria combine oxygen and sugar during cellular respiration to release energy ATP.

C6H12O6+6O6=> ATP+6C2O+6H2O

More active = More mitochondria

Each mitochondria has a double membrane. Outer membrane gives mitochondria its shape, and allows the flow of substances in and out of the cell. Inner membrane is folded into fine ridges which increase surface area for enzyme (responsible for energy production) attachment.

Centre of mitochondria (the matrix) is filled with fluid, which contains mitochondrial DNA and enzymes which allow it to replicate itself.

They divide by pinching off and then growing, usually occurring in very active cells.

Vacuole- storage and support

Large, permanent, fluid-filled sacs in the cytoplasm of mature plant cells.

Consists of a watery solution called cell sap (containing substances such as mineral salt, sugar and amino acids, surrounded by a single membrane (tonoplast).

Vacuole gives plants or flowers vibrant pigment.

Pressure on the cell wall keeping it firm (flaccid or turgid)

Chloroplasts- photosynthesis

Green in colour, due to presence of chlorophyll, which is responsible for photosynthesis.

Plant cell wall- shape and support

Cellulose cell walls are NOT selectively permeable.

Structure allows it to provide strength and support.

Strands of cellulose fibres have a little elasticity and are somewhat flexible (can resist pressure).

They are permeable for most molecules.

Centrioles- spindle production in cell division

Play an important role in cell division; forming the spindle which holds chromosomes in a dividing cell.

Cytoskeleton- keeps organelles in place

Organelle’s distribution is held in place by the cytoskeleton that extends through the cytoplasm.

Framework for cell shape, movement, organelle movement and cell division.

2.5 Cell Membranes - Gateway to Cells

The Fluid Mosaic Model

Model of the cell membrane, also known as the phospholipid bilayer

Controls the exchange of materials between internal and external environments.