A2.2 + B2.2 -ADDED

Plasma Membrane

The plasma membrane controls what enters and exits the cell. It is composed of phospholipids.

Cytoplasm

The Cytoplasm is the site of most metabolic processes. It is mostly composed of water.

80S Ribosomes

The 80S Ribosomes are responsible for protein synthesis.

Nucleus

The nucleus is the site of the chromosomes and DNA. It has a double membrane with pores which allows mRNA to enter the cytoplasm.

Chromosomes

Chromosomes are composed of DNA wrapped around histone proteins. The DNA is the genetic material with information for growth and development of the cell.

Mitochondria

Aerobic respiration, producing ATP

Vacoules

Plants have large vacuoles involved in storing nutrients. Small vacuoles are found in animal cells and are involved in the removal of waste

Lysosomes

Lysosomes are specialized vesicles, which contain enzymes. They are involved in the digestion of large molecules.

Rough Endoplasmic Reticulums

The rough endoplasmic reticulum is a membrane structure with ribosomes attached. It is the site of protein synthesis and is involved in transporting proteins to the Golgi Apparatus.

Smooth Endoplasmic Reticulum

The smooth endoplasmic reticulum is a membrane structure without ribosomes attached. It is involved in lipid synthesis and detoxification

Golgi Body

The Golgi Apparatus modifies and packages proteins to be exported from the cell.

Cytoskeleton

The cytoskeleton is composed of protein microtubules, and is involved in maintaining cell shape, moving organelles, and nuclear division (mitosis and meiosis)

Nucleus

 Contains DNA and is the site of transcription (DNA --> RNA). 

Cytoplasm

Contains ribosomes and is the site of translation (mRNA --> Proteins) 

The nucleus envelop separates transcription from translation, allowing

mRNA to be processed and regulated before it reaches ribosomes 

The nucleus also protects the DNA from

potentially damaging chemical reactions occurring in the cytoplasm. 

Prokaryotes do not have a nucleus, which means there is

no separation of the processes of transcription and translation

As mRNA is being transcribes, ribosomes attach to the

mRNA and translation can begin. 

Organelles are specialized structures which

compartmentalize different processes, allowing for greater efficiency  

Organelles provide a

protective environment for specialized activities in the cell. 

Organelles are able to store and use concentration of

metabolites and enzymes which are not compatible with metabolism occurring within the cytoplasm of a cell. 

 

Example 1: Lysosome 

The Digestive enzymes within a lysosome are capable of digesting other cell components. So they are

kept from separate from the cytoplasm and other cell structures by membrane surround lysosomes. 

Example 2: Phagocytic Vacuole (Phagosome) 

 

The potentially harmful material (e.g. bacteria) is kept inside a membrane-bound

 

compartment (phagosome) rather than being released directly into the cytoplasm 

Also, the phagosome concentrates the material being digested. Instead of having one bacterium or particle dispersed throughout a huge volume of cytoplasm, the material is

enclosed in a relatively small compartment. When lysosomes fuse with it, digestive enzymes are delivered where they are needed. 

Fungi have filamentous structure called hyphae, which may be separated by

internal cell walls called septa 

Some fungal hyphae are not separate by septa, forming one

long multinucleate cell. 

1. Skeletal Muscle Cell 

Skeletal muscle cells, also known as

muscle fibres, are multinucleate.  

1. Red Blood Cells (Erythrocytes)  

• • RBCs do not have a nucleus 

1. Phloem Sieve Tube Elements 

• • Phloem sieve tube elements do

not have a nucleus. 

Cell fractionation is a process which

separates cell organelles while preserving their functions. 

 Ultracentrifugation uses a fast centrifuge to

separate the cell organelles according to density 

  The development of ultracentrifugation 

 allowed scientists to study the function of individual organelles 

1. Cell Fractionation Steps 

• • Hommogenization: Tissue, containing cells, is broken up in a blender. The cells are . 

blended in a cold, buffered solution which is isotonic to the cytoplasm of the cells

• • The blended solution is filtered to

remove large cell debris. 

Ultracentrifugation Steps: 

  

1. The filtered solution containing the cell organelles is spun at low speed by an ultracentrifuge. 

2.    The densest organelles (nucleus) form a pellet at the bottom of the centrifuge tube. 

3.    The pellet is removed, and the process is repeated at faster speeds, producing a series of pellets containing one type of organelle each time.