Cells and compartmentalisation

Define prokaryotes

Pro = before, karyote = nucleus
Organisms which existed before the evolution of the nucleus.

What is the average size of a prokaryotic cell?

1-10 micrometers

Are prokaryotes compartmentalized?

No, they have no membrane bound organelles.

Define cell wall / capsule (prokaryote)

• Protects and maintains cell shape while preventing dehydration and adheres to surfaces.

• Made of peptidoglycan

Define nucleoid (prokaryote)

• Location of genetic material in prokaryotes.

• Naked, no histones.

Define plasmid (prokaryotes)

Extra circular piece of DNA

Define cytosol

The liquid part of the cytoplasm containing salts, sugars, fatty acids and proteins.

Define pili

Hair like structure made of proteins which enables attachments to surfaces and other bacteria.

Define flagella

Long protein filaments which rotate to allow bacteria to move.

What are the four components of all cells.

1. DNA
2. Cytoplasm
3. Ribosomes
4. Cell membrane

What is binary fission

Form of asexual reproduction where two genetically identical cells are produced.

Explain binary fission

1. The cell elongates and DNA is replicated
2. Cell wall and membrane begin to divide
3. Cross wall formation occurs and the DNA copies are completely separated
4. Two genetically identical cells separate.

Define Eukaryote

Eu = true , karyote = nucleus.
Cells where genetic material is stored in membrane bound nucleus.

What is the average size of a eukaryotic cell?

10-100 micrometers

Cell membrane

• Phospholipid bilayer embedded with proteins that surrounds the cell.

• Controls movement of substances in/out of cell.

Cell wall

• Rigid structure made of cellulose fibers, located outside the plasma membrane in plant cells.

• Provides structural support to plant cells and prevents them from collapsing or bursting.

Cytoplasm

• Jelly like substance mostly made of water which contains nutrients and enzymes.

• Fills the cell and is the site of many metabolic reactions.

Cytoskeleton

• Microscopic network of protein fibers extending throughout the cytoplasm that gives cells shape and support.

• Composed of three main types of protein fibers: microtubules, microfilaments and intermediate filaments.

Nucleus

• Controls activities of cell.

• Location of DNA packaged as chromatin.

• Surrounded by a double membrane (nuclear envelope) with many pores.

• Site of transcription of DNA into mRNA and contains nucleolus which contains RNA.

Centriole

• Pair of structures found near the nucleus of animal cells.

• Responsible for making the spindle microtubules which help the chromosomes separate during cell division.

Smooth Endoplasmic Reticulum

• Network of membranous tubes containing many enzymes.

• Produces lipids and steroid hormones.

• Helps detoxification of drugs in liver cells, and stores calcium needed fro muscle contraction in muscle cells.

Rough Endoplasmic Reticulum

• Network of membranous sacs embedded with 80s ribosomes.

• Site of synthesis of proteins which are to be secreted by the cell.

Golgi apparatus

• Made of flattened sacs of membrane called cisternae.

• Collects, modifies, packages and distributes materials made by the cell.

Vesicle

Tiny sacs of membrane that package and transport materials around the cell

Ribosome

• Site of translation of mRNA into polypeptides.

• Found free floating in cytoplasm and embedded in RER.

• Consists of large and small subunits made of rRNA and proteins.

Lysosome

• Sacs surrounded by membrane which contain many hydrolytic, digestive enzymes.

• They fuse or help break down damaged or old organelles, and help cells commit suicide.

• In phagocytes they help digest pathogens.

Mitochondria

• Rod-shaped organelle with its own DNA and 70s ribosomes.

• Have double membrane, where the outer is smooth and the inner is folded many times into CRISTAE.

• Site of aerobic respiration.

Chloroplasts

• Rod-shaped organelles with its own DNA and 70s ribosomes, which is only found in plant cells.

• Outer membrane is smooth and the inner is folded many times into THYLAKOIDS.

• Site photosynthesis

Vacuole

• Storage compartment found in all plant cells.

• Contains cell sap which is a mixture of water and solutes

• Helps to regulate the cell's turgid pressure and plays a role in breaking down cellular waste products.

Processes of life

Metabolism
Respiration
Sensitivity
Homeostasis
Growth
Reproduction
Excretion
Nutrition

Define organelle

Organelles are discrete structures in the cells that are adapted to perform a specific function. They can be solid structures or membrane bound sacs, enclosing specific combinations of dissolved molecules.

Define compartmentalisation

The organisation of different functions and processes within specific areas or structures in the cell that are separated by a plasma membrane.

What characteristics make organelles?

1. Discrete structures

2. Specific function

3. In the cells

What three structures aren’t organelles?

- Cell wall

- Cytoplasm

- Cytoskeleton

How was the nucleus formed?

Formed by a double infolding of the plasma membrane to sorround the DNA.

How were vesicles formed?

• Formed by a simple infolding of the plasma membrane during endocytosis, to absorb food particles.

• It formed a single membrane who’s contents come from the solution outside the cell.

How were mitochondria formed?

They were freeliving prokaryotes with their own membrane which were engulfed by endocytosis.

List the functions of the nucleus

1. DNA replication - makes copies of DNA ready for mitosis.

2. mRNA syntheisis - transcription

3. Modification of DNA - removal of introns and splicing

4. Delivery of mRNA to cytoplasm - through the nuclear pores

5. Sythesis of ribosomes - in nucleolus.

Where does DNA transcription occur in the nucleus?

Chromatin

State the advantages of compartmentalisation

1. Enzymes and metabolites can be concentrated in small spaces increasing chance of collision with substrate.

2. Substances that damage cells are isolated.

3. Conditions such as pH can be mantained at an optimal value

4. Large areas of membrane become dense with proteins for specific processes, so entry and exit of substances is controlled.

Explain the benefit of the compartmentalisation of lylosomes

• Lylosomes are enzymes that perform intra-celllular and extra-cellular digestion (hydrolisis).

• Lylosome enzymes are acid hydrolases and their optimal pH is 5, whereas the cytoplasm’s pH is 7.

• Separating them allows the cytoplasm’s content to remain functional at 7pH and prevents the acid hydrolases from denaturing.