MCB 1: Cells and Their Structural Organisation Flashcards
Describe the basic structure of the nucleus
- the nucleus consists of the nucleoplasm and the nucleolus
- enclosed by a double lipid bilayer, the nuclear envelope
- chromatin (unravelled chromosomes) are suspended in the nucleoplasm

Observe the diagram and learn the different structures of the nucleus

Look at the cross-section of the nucleus and its associated organelles
Label the missing parts


What is the function of the nucleolus?
Describe its structure
- it is the site of production of the subunits of the ribosomes
- it is an aggregate of the clusters of rRNA genes that are present at the ends of different pairs of chromosomes
- 5 pairs in humans: around 300 copies of the rRNA genes
- also contains the synthesised rRNA and proteins being assembled to make the ribosome subunits
Observe the TEM micrograph of the nucleus
What is the darker region?

- darker regions are heterochromatin
- these are regions of condensed DNA
- the DNA in these regions are generally less active
Where can ribosomes be present?
How does their function differ depending on where they are situated?
- free in the cytoplasm:
- synthesise cytoplasmic proteins
- attached to the outer membrane of the nuclear envelope and the endoplasmic reticulum:
- make membrane proteins and proteins to be packaged in membranous organelles
What are polyribosomes?
- multiple ribosomes binding to a single mRNA
- numerous copies of the polypeptide are produced from a single mRNA molecule
- translation starts at the 5’ to 3’ end
- when a stop codon is reached, the ribosome and amino acids dissociated from the mRNA
- see diagram

What are ribosomes composed of?
- two distinct subunits
- each of which contains rRNA (ribosomal) and protein
What is the composition and organisation of ribosomes in these organisms / structures :
- prokaryote
- eukaryote
- mammalian mitochondrial

What does the S unit stand for when talking about ribosomes

What is the relationship between the endoplasmic reticulum and Golgi apparatus?
- as seen on the diagram, there is a physical continuity between the nuclear envelope and the endoplasmic reticulum

What is this green mesh-like structure in the diagram?
Describe its function

- the nuclear lamina
- a specialised type of cytoskeleton formed on the internal surface of the nuclear envelope
- important in controlling the assembly/disassembly of the nuclear envelope in cell division
Describe the rough (granular) ER
- structure
- function

- generally occurs as stacks of flattened membrane leaflets (cisternae)
- studded on its outer face with ribosomes
- site of synthesis of membrane proteins and proteins to be packaged into membrane-bound structure e.g. secretory vesicles, lysosomes

Describe smooth (agranular) ER

- generally more tubular
- lacks attacked ribosomes
- specialises in detoxification and lipid metabolism
- enzymes involved are typically associated with the membranes
- the site of Ca2+ storage in cells
- important for cell-signalling contexts

Describe the golgi apparatus
- structure
- function
- a system of stacked, membrane-bounded flattened sacs
- cis face is aligned to the endoplasmic reticulum
- to receive vesicles from the ER
- trans face toward the cell periphery
- to direct vesicles to the rest of the cell and cell surface
Function:
- involved in modifying, sorting and packaging macromolecules for secretion or for delivery to other organelles

Describe the structure of the mitochondrion
Observe the micrograph: what is this?

- they do not always have the sausage-shape
- they can have elongated, complex, branched morphologies seen in the TEM micrograph
- note the spherical organelles called peroxisomes

What are peroxisomes?
Structure
Function
- present in most eukaryotic cells
Structure:
- enclosed by a single membrane
- contain enzymes involved in lipid and oxygen metabolism
- oxidases, catalases, peroxidases
- the enzymes can be present at such high concentrations that they ‘crystallise’ to form the cores observed in the TEM micrograph
Function:
- important in oxidation reactions
- by-product of the reactions is peroxide

What is the cytoskeleton?
What are the three main types?
- a system of filaments formed by the polymerisation of protein monomers
- three main types:
- microtubules
- intermediate filaments
- microfilaments

Observe these fluorescence micrographs of cytoskeleton organisation in animals cells

Where can I find more basic info on the cytoskeleton?
- check MCB 1 E-modules
Describe how life came to be
- watch the video in MCB 1

What is the thickness of
- human hair
- animal cells
- bacterial cells

What is the thickness of ribosomes and the cellular bilayer?

Compare the eukaryote and prokaryote micrograph















