3.2, 3.3, 3.5 Eukaryotic Cells

Spec point 3.2: "Know the ultrastructure of eukaryotic cells, including nucleus, nucleolus, ribosomes, rough and smooth endoplasmic reticulum, mitochondria, centrioles, lysosomes, and Golgi apparatus"

What does ultrastructure mean?

The internal structure of cells

What type of microscope is needed to view the ultrastructure of cells?

electron microscope

Eukaryotic cells have a ____ complex ultrastructure than prokaryotic cells

more

Key differences between eukaryotic and prokaryotic cells

Prokaryotic cells are:
- smaller
- lack membrane bound organelles
- have smaller ribosomes
- no nucleus
- cell wall contains glycoprotein murein whereas eukaryotic plant cell walls are made of cellulose

Which types of cells are eukaryotic?

Plant cells, animal cells

Key differences between animal and plant cells include

• animal cells contain centrioles and some have microvilli while plant cells do not

• plant cell have a cellulose cell wall, large permanent vacuoles and chloroplasts while animal cells do not

What are microvilli (present in some animal cells?

folded regions of the cell surface membrane that increase cell surface area for absorption
e.g. in the small intestine

What parts of the ultrastructure of an animal cell do you need to know?

nucleus, ribosomes, mitochondria, cell/plasma membrane, centrioles, vesicles, lysosome, rough endoplasmic reticulum, smooth endoplasmic reticulum, golgi apparatus

Features of a nucleus

• nuclear envelope

• nucleolus

• chromatin

• nuclear pore

Features of the nucleus: What is the nuclear envelope?

a double membrane which separates the nucleus from the cytoplasm
it contains many pores

Features of the nucleus: Why are nuclear pores important?

They are important channels which allow mRNA and ribosomes to travel out of the nucleus, as well as allowing enzymes and signalling molecules to travel in

Features of the nucleus: What is chromatin?

Linear DNA and proteins- this is the material from which chromosomes are made

Features of the nucleus: What is the nucleolus

a dense region which is the site of ribosome production

What is the nucleus surrounded by?

The endoplasmic reticulumD

Function of nucleus

control cell activities

Diagram of nucleus

Function of the cell surface/plasmid membrane

• controls the exchange of materials between the internal cell environment and the external environment

The cell surface membrane is described as being _________ _________, meaning that…

partially permeable
some substances can pass through the membrane while others cannot

The cell surface membrane is formed from a…

phospholid bilayer spanning a diameter of around 10nm

Function of mitochondria

• site of aerobic respiration

  • responsible for producing ATP, the primary energy currency of the cell

What type of membrane does mitochondria have?

a double membrane

The inner membrane of the mitochondria is folded to form structures called…

cristae

Diagram of mitochondria

Where are ribosomes found?

they can be found as free organelles in ALL cells or as part of the rough endoplasmic reticulum in EUKARYOTIC cells

Are ribosomes surrounded by a membrane?

no

Ribosomes are composed of…

RNA and proteins

Difference between ribosomes in eukaryotic vs prokaryotic cells

ribosomes are larger in eukaryotic cells (80s) and smaller in prokaryotic cells (70s)

Function of ribosomes

• site of translation

• where proteins are made

Two types of endoplasmic reticulum

rough (RER)

smooth (SER)

Both the SER and RER are formed from…

folds of membrane formed as an extension of the outer membrane of the nuclear envelope

The surface of the RER is covered in…

ribosomes

What is the role of the RER?

to process proteins made on the ribosomes

Function of SER

• involved in the production, processing and storage of lipids, carbohydrates and steroids

Diagram of endoplasmic reticulum

What is the golgi apparatus made of?

flattened sacs of membrane

Role of the golgi apparatus

• modify proteins and lipids before packaging them into golgi vesicles

  • vesicles are often seen at the edges of the sacs, these then transport the proteins and lipids to their required destination

Diagram of golgi apparatus

What are lysosomes?

• specialist forms of vesicle which contain hydrolytic (digestive) enzymes

Role of lysosomes

• to break down waste materials such as worn out organelles

Lysosomes are used extensively by cells of…

the immune system and in programmed cell death, known as apoptosis

Structure of lysosome

no clear internal structure

Centrioles are made of…

hollow fibres known as microtubules

Microtubules are…

filaments of protein that can be used to move substances around inside a cell, as well as to support the shape of a cell from the inside

Two centrioles at right angles to each other form a…

centrosome

What does a centrosome do?

organise the spindle fibres during cell division

Are centrioles found in plants and fungi?

no

Diagram of centriole/centrosome

Which organelles are involved in the production and secretion of proteins?

nucleus

• transcription of DNA code

ribosomes

• produce proteins in the process of translation

RER

• where proteins are synthesised and transported to golgi apparatus

golgi apparatus

• modifies, packages and sorts proteins

• sends repackaged proteins to final destination, either via transport vesicles or by incorporating them into the plasma membrane

identify the organelles in this EM image