Cellular Bio (I): A2.2 Cell Structure

Define light microscopy

Uses light to pass through a living or dead specimen to form an image

Define electron microscopy

Uses electrons passing through a dead specimen to form an image, producing the greatest magnicifcation and resolution

Objective lens vs length of one eye piece graticule division (microm)

x4 - 25 um
x10 - 10 um
x40 - 2.5 um

Formula for magnification

Magnification = image size / real size (same units)

Outline 2 developments in light microscopy

Fluorescent stains: highlights specific structures using dyes that bind selectively; allows for higher clarity and visibility of specimen; live cell imaging if non-toxic dyes are used

Immunofluorescent stains: uses antibodies tagged with fluorescent dye to bind with proteins; high specificity of locating molecules; enables study of protein localisation, interactions and abundance

Outline 2 developments in electron microscopy

Freeze fracture: reveals internal structures of cell membrane; used to visualise integral proteins; insight into protein asymmetry and distribution

Cryogenic microscopy: preserves samples in near native state; used for fragile and delicate samples; used for biological molecules such as proteins and viruses

State the advantages and disadvantages of electron microscopy:

Advantages: high resolution and magnification

Disadvantages: only black and white images, complex and elaborate sample prep; high maintainance cost; only dead speciment can be imaged

State the advantages and disadvantages of light microscopy:

Advantages: simple to prepare sample; low cost; specimen can be dead or alive

Disadvantages: limited magnification; limited by the wavelength of light

Outline the structures common to both prokaryotic cells and eukaryotic cells:

1. DNA as genetic information: contains genetic information required for mRNA to be translated and transcripted to synthesis proteins

2. Plasma membrane: controls movement of substances in and out of the cell; partially permeable

3. Cytoplasm: site of cellular activity - metabolism

Describe the features and functions of the nucleoid of the prokaryotic cell:

Central region of cytoplasm, naked single circular chromosomal DNA

Describe the features and functions of 70S ribosomes in prokaryotic cells

Granular appearance in electron microscope

Synthesises proteins through transcription and translation

Describe the form and function of the cytoplasm in prokaryotic cells

Carries out chemical processes of metabolism using enzymes and molecules

contains enzymes and ribosomes; no membrane bound organelles

Describe the features and functions of the cell wall in prokaryotic cells

Made up of peptidoglycan; semi rigid

maintains shape of cell and protects interior; prevents bursting

What are the functions of life (MR SHENG)

Metabolism
Reproduction
Sensitivity
Homeostasis
Excretion
Nutrition
Growth

Describe the features and functions of the nucleus in eukaryotic cells:

Contains chromosomes which contain genetic information

Enveloped in the nuclear envelope (double membrane), which has pores which controls the rate of translation and transcription

Contains nucleolus

Describe the features and functions of the nucleolus in eukaryotic cells:

Contains DNA that codes for rRNA for the synthesis of ribosomes

Site of rRNA synthesis, processing and assembly of ribosomes

Describe the features and functions of the RER in eukaryotic cells:

Network of cisternae

Ribosomes attached to surface for synthesis of proteins which are secreted out of the cell

Continuous with nuclear envelope

Transport proteins to Golgi via transport vesicles

Describe the features and functions of the SER in eukaryotic cells:

Cisternae, smooth

Modifies glycolipids and glycoproteins

Packages proteins into vesicles for secretion out of the cell

Produces lysosomes

Produces macromolecules e.g. pectin

Describe the features and functions of the mitochondrion in eukaryotic cells:

Smooth outer membrane with inner foldings called cristae to increase SA:V for oxidative phosphorylation

site of link reaction, Kreb's cycle and oxidative phosphorylation of cellular respiration for ATP respiration

Describe the features and functions of chloroplasts in eukaryotic cells:

Double membrane, contains thykaloids

Contains chlorophyll - site of photosynthesis

Describe the features and functions of lysosomes in eukaryotic cells:

Contains hydrolytic enzymes

Digests material by phagocytosis
Digests unwanted/dead organelles
Releases enzymes from cells

Describe the features and functions of the cytoskeleton in eukaryotic cells:

Microtubules

• made of tubulin, maintain cell structure and shape

Microfilaments

• made out of actin, maintains shape of cell

Also important during cell division

Describe the functions of free 80s ribosomes in eukaryotic cells:

Synthesises proteins which are used within the cell

Describe 3 adaptations of specialised cells:

RBC: no nucleus more space for haemoglobin higher capacity to bind with oxygen, limited lifespan

Skeletal muscle: many mitochondria to synthesise more ATP for muscle contraction

Phloem sieve tube elements: nucleus breaks down so that sap can flow more easily

State the endosymbiotic theory

Eukaryotic cells evolve from bacterial cells engulfing prokaryotic cells via phagocytosis.

Outline the evidence for the endosymbiotic theory (MADDR)

Membranes: both have plasma membrane
Antibiotics: both susceptible
Division: both divide by binary fission
DNA: both contain circular naked DNA
Ribosomes: both have ribosomes (70 or 80S)

How do specialised tissues in multicellular organisms arise

Changes in environment - different patterns of gene expression are triggered, cell differentiation with new properties emerge, form tissues - organs

Describe 3 advantages of multicellularity

Longer lifespan - the death of one cell does not prevent the survival of the individual

Larger - exploit niches

Complexity - differentiation of cell types