Cell Structure & Diversity.

Unicellular

An organism consisting of just one cell.

Multicellular

An organism consisting of many cells.

Eukaryotic

Contain a nucleus and membrane-bound organelles.

Prokaryotic

Contain no nucleus or membrane-bound organelles. Their genetic material is present as a nucleoid ( a loop of DNA ).

Organelles

Structures within cells which carry out a particular role.

Animal Cells

• Do not have a cell wall.

• Do not have chloroplast.

• Contain small, non-permanent vacuoles.

Plant Cells

• Do have a cell wall.

• Do have chloroplasts.

• Contain large, permanent vacuoles.

Cell Ultrastructure

The structure of a cell seen under an electron microscope.

A Transmission Electron Microscope

Shows the internal structure of a specimen.

A Scanning Electron Microscope

Shows the surface of a specimen.

Electron Micrograph

A photograph or digital image taken through an electron microscope.

Antigen markers

Proteins on the surface of cell membranes to allow the cell to be identified as part of the body, so that it is not attacked by the body’s immune system.

Semi-permeable

Allows small molecules ( e.g water or oxygen ) to pass through the cell, but larger molecules cannot.

Selectively permeable

It can actively control which of those larger molecules can enter and exit the cell.

Nucleus

• Control centre of the cell and home to the cell’s genetic material.

• Wrapped in a phospholipid membrane, which has small openings called nuclear pores.

• These allow materials, like RNA, to pass in and out of the nucleus.

• Nucleolus is found within the nucleus and produces a type of RNA.

• Contains DNA found in structures called chromosomes.

• The DNA is wrapped around proteins called histones.

• When DNA is unwrapped it is called chromatin.

Mitochondria

• Organelles responsible for cellular respiration, the release of energy from food.

• Energy from the breakdown of food is trapped in a molecule called ATP.

• Contain an outer membrane and a folded inner membrane.

• The inner membrane is folded into structure called cristae.

Ribosomes

• Organelles responsible for protein synthesis.

• Made of ribosomal RNA ( rRNA ) and proteins.

Endoplasmic Reticulum

• A membrane-bound organelle responsible for protein and lipid synthesis, and transportation.

• Consists of a set of interconnected tubes called cisternae and is a production sit for important cellular fats, like phospholipids and cholesterol, as well as steroid and hormones.

• Rough endoplasmic reticulum is covered in ribosomes.

• ER without ribosomes is called smooth endoplasmic reticulum.

Golgi Apparatus

• Packages the proteins and lipids manufactured in the ER and moves them to other parts of the cell or outside the cell.

• Consist of stacks of membrane-bound sacs called cisternae, this time they are not interconnected.

• Exist in both animal and plant cells.

Cell Wall

• Provides strength and support to the cell.

• Fully permeable, meaning all substances pass through it.

• Made from a complex carbohydrate called cellulose.

• Fungi have cells with a cell wall composed of chitin.

Chloroplasts

• Organelles responsible for photosynthesis.

• Contain a double membrane and a loop of DNA.

• Inside is a liquid called stroma and stacks of green pancake like structures called thylakoids.

• A stack of thylakoids is called a granum.

Vacuoles

• Plant cells contain large permanent vacuoles.

• Filled with a fluid called cell sap.

• Sap contains water, dissolved sugars and salts and waste materials.

• The pressure exerted on the wall by the vacuole is called turgor.

Light Microscope

• Eyepiece lens - Specimen is viewed through here.

• Objective lens - Magnifies the specimen.

• Stage - Holds the slides.

• Slide - Holds the specimen.

• Coverslip - Protects the lens from the stain.

• Course focus wheel - Brings specimen into rough focus.

• Fine focus wheel - Brings specimen into sharp focus.

• Light source - Provides light to view the slide.

Cell diversity

Multicellular organisms contain different types of cells.

Tissue

A group of similar specialised cells, carrying out a specific function.

Organ

Contains a group of different tissues working together to preform a specific function.

Organ system

Consists of multiple organs co-operating to carry out a specific function.

Stem Cells

• Unspecialised cells in the body.

• They have the potential to transform into any type of cell.

• Plants also contain stem cells, within the meristem of their roots, stems and leaves.

What are the types of Stem Cell ?

1. Pluripotent stem cell.

2. Multipotent stem cell.

3. Cloning stem cells.

4. Induced pluripotent stem cells.

Pluripotent stem cells

Give a rise to all the cell types that make up a human body. Embryonic stem cells are and example of pluripotent stem cells.

Multipotent stem cells

• Can develop into a limited number of cell types.

• Haematopoietic stem cells can only produce blood cells (red blood cells, white blood cells, etc)

Cloning stem cells

• Do not naturally occur in the body. Instead, they are artificial copies of cells.

• Produced using a process called somatic cell nuclear transfer (SCNT), where the nucleus of a somatic cell is transferred into an egg cell whose own nucleus has been removed.

• This creates an embryo that is a genetic clone of the donor.

Induced pluripotent stem cells

Begin as a somatic cell (e.g muscle or blood cell) but are converted into pluripotent stem cells by scientists.

What are the Therapeutic Uses of Stem Cells ?

• Can be transplanting into a patient to repair damaged tissue.

• Could be used to treat Parkinson’s disease, diabetes or spinal cord injuries.

• Pluripotent, cloning and induced pluripotent stem cells have the greatest potential for therapy, as they can be turned into any kind of body cell.