Cells and Tissues

Published on 23rd April 2018

  THE CELL

  • Is the basic living, structural and functional unit of the human body 
  •  It is the activity within the cell which constitutes what is called life

 

FUNCTION 

  • To produce protein to: 
    • Work 
    • Replace itself for growth, repair and renewal 
  • Breakdown in the proper functioning of cells is the basis of disease

ANATOMY

  • Made up of: 
    • 80% water
    • 15% protein
    • 3% lipids (fats)
    • 1% carbohydrates
    • 1% nucleic acid and minerals 
  •  All cells have a similar basic construction 

 

THE CELL CONSTRUCTION

 

1. CELL MEMBRANE

  • Porous sandwich of fat and protein

2. RIBOSOMES

  • Controls construction of essential proteins needed by cells for repair and renewal 

3. GOLGI APPARATUS

  • Packages proteins that the ribosomes have made

4. ENDOPLASMIC RETICULUM

  • Internal transport system of the cell

5. LYSOSOMES

  • Sacs filled with enzymes

6. NUCLEUS

  • Embedded in the Cytoplasm  
  • Supervises cell activity – the ‘brain’ of the cell  
  • Surrounded by nuclear membrane 

7. MITOCHONDRIA

  • “The Powerhouse of the cell!”   Converts oxygen and nutrients into energy through action of enzymes

8. CYTOPLASM

  • Jelly like “filling” made of 70~80% water

9. CHROMOSOME (found within nucleus)

  • Begin as structures called chromatids which are two parallel filaments joined together at the centromere  
  • Made up of strands of DNA.  Small parts of these DNA strands are called genes  
  • There are 46 chromosomes in 23 pairs in every cell (except sperm and ovum)

 

CELL REPRODUCTION

TWO PROCESSES:

MEIOSIS

  • Sperm and ova are formed by MEIOSIS
  • A 7 stage process
  • Where a parent cell with 46 chromosomes divides to produce 4 daughter cells with 23 chromosomes each

MITOSIS

  • All other cells reproduce themselves by MITOSIS
    • 23 pairs of chromosomes – shorten, thicken and split.  Each one duplicates its own DNA
    • The duplicated chromosomes separate and move to opposite ends of cell
    • Cytoplasm is halved – 2 daughter cells 

 

DEVELOPMENT OF THE HUMAN BEING

1. EPITHELIUM TISSUE

  • Simple Epithelium 
    • Squamons
    • Cuboidal
    • Columnar
    • Ciliated 
  • Compound Epithelium    
    • Stratified
    • Transitional 

2. CONNECTIVE TISSUE

  • Areolar
  • Adipose
  • Bone
  • Blood
  • Cartilage
  • Elastic (yellow)
  • Fibrous (white)
  • Lymphoid 

 3. MUSCULAR TISSUE

  • Striated
  • Smooth (non-striated)
  • Cardiac 

4. NERVE TISSUE

5. MEMBRANES 

These are sheets of epithelial tissue which cover or line internal and external structures and cavities. 
 
The three main membranes are;

  • Mucous
  • Serous
  • Synovial 

 

Overview of cell organelles – Revision Aid

Cell Theory: All known living things are made up of cells. All cells come from pre-existing cells by division. The cell is structural and functional unit of all living things. 
 
Cytoplasmic Organelles:  
Are compartmentalized structures that perform a specialized function within a cell. 
 
Nucleus:  
The nucleus contains a nucleolus and is separated from the cytoplasm by the nuclear envelope. The nucleus contains the cell’s DNA, a type of nucleic acid. The nucleolus is like a “tiny nucleus” inside the actual nucleus. It contains RNA, a type of nucleic acid. The nucleus communicates through holes in the envelope called nuclear pores. The nucleus decides what the cell needs and uses DNA to print out instructions for the rest of the cell to produce that need. 
 
Chromosomes:
Hold the cell’s DNA in the nucleus. The nucleus contains genetic information in the form of DNA (the universal genetic code). The DNA does not hang around loosely in the nucleus. The DNA is packaged with proteins and wound up. Recall that the role of nucleic acids is to carry genetic information, which is inherited by an organism’s offspring. These wound up DNA protein structures are called chromosomes. 
 
Golgi apparatus:  
Ships packages around the cell. The golgi is made up of flattened, folded sacs. Packages (e.g. containing proteins) are carried to the golgi in vesicles. The golgi receives an incoming vesicle, tags the package, and sends the vesicle to its final destination. 

Lysosome:  
Destroys waste to clean up the cell.  Vesicles carry the waste (bacteria, old organelles, etc.) into the lysosome. Once inside, the waste is destroyed and its parts recycled. 

Endoplasmic reticulum:
Two types of ER make different building blocks for the cell. Smooth ER is NOT attached to the nucleus and DOES NOT have attached ribosomes (thus smooth). Smooth ER synthesizes carbohydrates (sugars) and lipids (fats).  Rough endoplasmic reticulum: Rough ER is found attached to the outside of the nucleus. It appears rough because of the ribosomes on its surface. Rough ER helps the attached ribosomes in finishing protein synthesis 

Mitochondria:
Produce energy to power the cell. The mitochondria convert carbohydrates (sugar) taken from food into ATP. The mitochondria are unique in that it has two protective shells.  

Ribosomes:  
Make proteins for the cell.   The ribosome reads the DNA strand instructions to make proteins for the cell to use in its normal activities. The units clasp around a strand of nucleic acid instructions from the nucleus. Each ribosome is made of two protein subunits. 

Cell membrane:
A selectively permeable structure that envelops the cell and protects the cell’s internal environment. Plasma Membrane, the cell’s membrane is made of phospholipids, which have carbohydrate heads and lipid tails. Embedded proteins are anchored to the cell membrane. Provides a stabilized environment, which protects and maintains the cell’s internal environment, separate from the environment outside. Proteins embedded into the membrane send and receive signals to communicate with other cells. 

 

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