Chap 1 - The Cell cycle, cell junctions & microscopy

How long is the period of cell cycle?

18 - 22 hours during which the cell can synthesise new DNA and partition the DNA equally

What is mitosis involved in?

nuclear division (karyokinesis) follow by cell division (cytokinesis)

which phase does mitosis and cytokinesis define?

the mitotic phase of the cell cycle

what occurs in the mitotic phase?

the division of the mother cell into two daughter cell, genetically indentical to each other and their parent cell

What are the phases in the cell cycle?

interphase (G1, S and G2) and mitosis (prophase, metaphase, anaphase and telophase)

How much does interphase occupy in the whole cell cycle?

about 90%

what happens in interphase?

the cell prepare for DNA synthesis known as G1

what happens in S phase?

synthesise and replication of DNA, results in the duplication of chromosomes

what happens in G2?

prepares for mitosis

what happens to the DNA in interphase?

the DNA is not folded and the individual chromosomes are not visible, centrioles grow to matrue, RNA and protein for mitosis are synthesised

Where does mitosis begins?

prophase

what occurs in prophase?

Centrioles move to opposite poles and organise microtubules to form the mitotic spindle, with astral microtubules radiating from the centrosomes (MTOCs). Chromatin condenses into visible chromosomes, each consisting of two identical sister chromatids joined at the centromere, where kinetochores form for spindle attachment. By the end of prophase, the nuclear envelope breaks down, allowing spindle fibres to interact with chromosomes.

what happens in metaphase?

centromeres line up along the equatorial plate, near the centromeres are kinetochores which are proteins that face the spindle pole. Microtubules, from the spindle, attach to the kinetochores of each chromosomes

what happens in Anaphase?

sister chromatids are pulled apart, each migrate to opposite poles by spindle microtubules.

what happens at the end of Anaphase?

a cleavage furrow forms around the cell due to contraction of actin filaments called the contractile ring

What happens in telophase?

new membranes form around the daughter nuclei, nucleoli reappear, the chromosomes uncoil and become less distinct.

what happens at the end of telophase?

the cleavage furrow becomes deepened, facilitating the division of cytoplasm into two daugther cells, each with a nucleus and organelles

what happens in cytokinesis?

cell separation occurs, the cell continues with the next interphase

What are cell junctions?

they are especially abundant in epithelial tissues and serve as points of contract between cells.

what is the purpose of cell junction?

the multi protein complex that comprise cell junctions can also build up the barrier around epithelial cells and control paracellular transport

what are the molecules responsible for creating cell junctions?

cell adhesion molecules (CAMs),this helps cells to stick to each other and to their surroundings.

what are the four main types of cell adhesion molecules?

selectins, cadherins, integrins and the immunoglobulin superfamily

what are the three main types of cell junctions?

1. Anchoring junctions

2. Communicating junctions

3. Occluding junctions

what are anchoring junctions?

1. Adherens junction

2. desmosomes

3. hemidesmosomes

what are communicating junctions?

Gap junctions

what is occluding junctions?

Tight junctions

what are adherens junction?

they link to the actin cytoskeleton

what are desmosomes?

cell adhesion proteins like cadherins which bind intermediate filaments and provide mechanical support and stability

what are hemidesmosomes? (hemi=half)

attach one cell to the extracellular matrix (usually anchoring the 'bottom’ or basal aspect of the epithelial cell or keratinocyte to the basement membrane.

what are gap junctions?

narrow tunnels which allow the free passage of small molecules and ions

what are tight junctions?

junctional complex that join together forming a virtually impermeable barrier to fluid, join together the cytoskeletons of adjacent cells. they surround the upper part of the lateral surfaces of adjacent epithelial cells.

what are the two popular methods of microscopy utilised by the vast majority of molecular biology research?

1. the optical or light microscope

2. the electron microscope (the transmission electron microscope or TEM and the scanning electron microscope or SEM)

what is magnification?

how much bigger the image appears

what is resolution?

the ability to distinguish between two points on an image

What is light microscopy?

A microscopy technique that uses visible light and lenses to magnify specimens, allowing observation of live cells.

What controls the amount of light reaching the specimen in a light microscope?

The iris diaphragm.

What is the function of the condenser lens?

It focuses the light beam through the specimen.

What is the role of the objective lens?

It magnifies the image of the specimen.

What are the two key terms associated with microscopy performance?

Magnification and resolution.

Why is light microscopy popular?

It is relatively low cost, easy to use, and can view living specimens.

What is a major limitation of light microscopy?

Limited magnification and resolution.

What is the SI unit of length?

Metre (m).

What does 1 µm (micrometre) equal?

10^−6 m.

What does 1 nm (nanometre) equal?

10^−9 m.

What does 1 Å (angstrom) equal?

10^−10 m.

What does 1 pm (picometre) equal?

10^−12 m.

Is the term “micron” still used technically?

No — micrometre (µm) is the correct term.

Why is electron microscopy less commonly used?

It is expensive, complex, and requires a vacuum.

Can electron microscopy be used on living organisms?

No — specimens must be dead.

What particles are used instead of light in EM?

Electrons.

Are EM images naturally coloured?

No — they are black and white (colour may be added artificially).

What is the key advantage of electron microscopy?

Extremely high magnification (up to ~10,000,000×) and very high resolution.

What resolution can EM achieve?

Approximately 50 picometres.

What does TEM show?

The internal structure of cells (thin sections).

What does SEM show?

The surface structure of specimens.

What is the axoneme arrangement in cilia and flagella?

9 + 2 arrangement (9 doublets + 2 central microtubules).

What protein enables movement in cilia and flagella?

Dynein.

What is fluorescent microscopy used for?

dentifying specific cellular components with high specificity and colour.

How does fluorescent microscopy work?

Fluorophores are excited by high-intensity light and emit light at specific wavelengths.

What special component does a fluorescent microscope use?

Filters that allow only specific excitation and emission wavelengths.

Is fluorescent microscopy a type of light microscopy?

Yes — it is an optical microscope.

What is immunofluorescence?

A technique that uses antibody–antigen specificity to locate molecules in cells using fluorescent dyes.

What biological principle does immunofluorescence rely on?

Specific binding between antibodies and antigens.

What can immunofluorescence be used on?

Tissue sections, cultured cells, or individual cells.

What is another term for immunofluorescence on tissues?

Immunohistochemistry.

What is a fluorophore?

A fluorescent chemical that emits light when excited.

What is direct immunofluorescence?

A single antibody directly linked to a fluorophore binds the antigen.

What is indirect immunofluorescence?

A secondary antibody (with fluorophore) binds to a primary antibody attached to the antigen.

Which method gives stronger signal amplification?

Indirect immunofluorescence.

what are the two antibodies indirect immunofluorescence use?

1. the unlabeled first, or primary, antibody binds the antigen

2. carries the fluorophore and recognises the primary antibody and binds to it

what is photobleaching?

is the photochemical destruction of a dye or a fluorophore

how is the fluorescent molecules destroyed?

by the light exposure necessary to stimulate them into fluorescing

what is photobleaching use for?

to study the motion of molecules

what is a confocal microscope?

is a state of the art fluorescent microscope which uses a laser as the light source

what are FRAP used for?

studies of cell membrane diffusion and protein binding, determining if axonal transport is retrograde or anterograde (meaning towards or away from the neuron’s cell body (soma))