1. Cells and cell structure

What is the structure of a phospholipid?

• 2 fatty acids chains and a phosphate bonded to glycerol molecule

• Amphipathic:

  • Nonpolar, hydrophobic fatty acid tails

  • Charged, hydrophilic phosphate head

How do phospholipids structure themselves when added to water?

Form bilayers:

• Hydrophilic phosphate heads face water

• Hydrophobic fatty acid tails in the middle

What is the role of the phospholipid bilayer?

• Separates the cytoplasm and cell contents from the environment

• Acts as a barrier for materials entering and exiting the cell

• Only hydrophobic/uncharged particles can pass through hydrophobic fatty acid tails

• Large/hydrophilic/charged particles cannot pass directly through

What is the kinetic theory?

• Particles are in constant motion

• Particles in gases, liquids, solutes in aqueous solutions move in random directions

• Random movement of particles leads to diffusion and osmosis

What is diffusion?

Passive transport of particles from high to low concentration

What are integral proteins?

• Permanently attached to the plasma membrane

• Penetrate into the centre of phospholipid bilayer

• Contain 1 hydrophobic section and 2 hydrophilic sections

• Can be transmembrane or only partially penetrate bilayer

• Can be glycoproteins/channels/protein pumps

What are peripheral proteins?

• Temporarily attached to membrane surface/integral proteins through electrostatic interactions

• Attracted to charged sections of integral proteins and phosphate heads

• Hydrophilic, do not penetrate the phospholipid bilayer

• Can be receptors and enzymes

What is osmosis?

Passive transport of water molecules from low to high solute concentration through a semipermeable membrane

What are aquaporin?

• Integral channel proteins that selectively transport water rapidly through membranes

• Significantly increases membrane permeability to water

What is facilitated diffusion?

Passive transport of molecules from high to low concentration through channel proteins

What are channel proteins?

• Specific to the molecule that can pass through them - selectively permeable

• Have central pore which allows specific particles to move through - lined with hydrophilic amino acid R groups that allow one type of molecule to pass through

• Some are gated - only open to allow facilitated diffusion in response to a stimulus

What is Adenosine Triphosphate (ATP)?

Provides energy required to change shape of protein pumps for active transport in cells

What is active transport?

Movement of particles from low concentration to high concentration using protein pumps and ATP energy

What is the process of active transport?

• Particle binds to binding site on protein pump

• ATP binds to protein pump, hydrolyses → ADP

• Phosphate attaches to protein pump, causes pump to change shape

• Particle moved against concentration gradient and released

• Phosphate released → protein pump returns to original shape

What are examples of selectivity in membrane permeability?

• Facilitated diffusion: selective

• Active transport: selective

• Simple diffusion: not selective

What are glycoproteins?

Membrane proteins with carbohydrate chain attached

What are glycolipids?

Phospholipids with carbohydrate chain attached

What are the roles of glycoproteins and glycolipids?

• Receptors for hormones

• Cell to cell communication: bind to neurotransmitters

• Immune response: act as markers on cells

• Cell to cell adhesion: form tissues

How are glycoproteins and glycolipids involved in cell recognition?

• Carbohydrate chains have specific shapes that allow immune system to recognise cells as self

• Act as antigens if carbohydrate chain is not recognised as self

What is the fluid mosaic model?

• Phospholipids and proteins can move around

• Proteins embedded like mosaic

• Helps to explain passive + active movement between cells and surroundings, cell to cell interactions, cell signalling

What is the role of cholesterol in animal membranes?

• Stabilises by reducing extremes of fluidity

• Prevents too much permeability at high temps

• Prevents freezing at low temps

• Positioned between phospholipids with OH group near heads

What cells structures are not considered organelles?

• Cell wall: extracellular structure

• Cytoplasm: gel-like fluid

• Cytoskeleton: found throughout cell

What are organelles?

Specialised units performing specific roles

What are the benefits of separating the nucleus and cytoplasm?

• DNA is kept safe in nucleus

• Transcription in nucleus → translation in cytoplasm

• Allows post-transcriptional modification (splicing, capping, tailing)

What are the advantages of compartmentalisation?

• Enzymes + substrates concentrated → faster reactions

• Harmful substances isolated (e.g. lysosomal enzymes)

• Optimal local conditions (e.g. pH in lysosomes vs cytoplasm)

• Organelles can move to where needed

What is fertilisation?

• Fusion of gametes

• Leads to development of a zygote

What are stem cells?

• Unspecialised/undifferentiated cells

• Can continually divide and replicate

• Have the capacity to differentiate into specific cell types

• Found in skin, testes, and other tissues

What are the differences between adult and embryonic stem cells?

• Adult: less ethical issues, lower chance of graft rejection, lower potency

• Embryonic: greater potency but ethical issues involved with their use

What are stem cell niches?

Locations in the body where stem cells can be maintained/promoted to proliferate and differentiate

What are examples of stem cell niches?

• Bone marrow: hematopoietic cells can differentiate into all types of blood cells

• Hair follicles: epidermal stem cells that self-renew, differentiate, regulate hair growth, maintain skin homeostasis

What are the three main types of stem cells?

• Totipotent

• Pluripotent

• Multipotent

What are totipotent stem cells?

• Can differentiate into all types of cells/develop into an embryo

• E.g. zygotes

What are pluripotent stem cells?

• Can differentiate into all types of cells but do not develop into an embryo

• E.g. embryonic stem cells

What are multipotent stem cells?

• Can differentiate into a limited range of cells

• E.g. adult stem cells

What are examples of specialised human cells?

• Sperm: smallest cells in body, long + thin for motility

• Egg: cell with largest volume, nutrient reserves

• Neurons: long axons for fast transmission

• Red blood cells: biconcave, small volume, larger surface area to volume ratio → efficient gas exchange

• Muscle fibres: long, multinucleated → strong contraction

What are the implications of the SA:V ratio?

• Metabolic rate depends on cell volume

• Exchange rate depends on surface area

• Low SA:V slows exchange and causes waste accumulation

What is the cell theory?

• All living things are composed of cells

• Cells are the basic units of structure and function

• Cells come from preexisting cells

What is resolution?

Ability of a microscope to distinguish details of a specimen or sample

What is the magnification formula?

Actual length = Measured length / Magnification

What are the conversions of mm, µm and nm?

1000μm = 1mm

1000nm = 1 μm

What is the difference between electron and light microscopes?

• Light: less magnification, less resolution, colour images

• Electron: more magnification, more resolution, black and white images

What is cryogenic electron microscopy?

Allow scientists to view proteins and other biomolecules which do not readily crystallise

What is freeze fracture electron microscopy?

• Technique used to examine ultrastructure of rapidly frozen biological samples e.g. plasma membranes

• Membranes are rapidly frozen → fractured in area of weakness

• Analyse structure of plasma membranes, identify integral proteins

What is immunofluorescence?

• Technique used to visualise specific protein/antigen in cells/tissue

• Bind specific antibody chemically attached to fluorescent dye

• Antibodies attach to specific proteins within biological tissue

• Sample can be analysed using a fluorescence microscope

What are the advantages of immunofluorescence?

• Specific: can study location, distribution, quantity of biomolecules

• Can be used with living tissue: study dynamic processes e.g. cell division

• Detect molecules at low concentrations

What are features that all cells share?

• Phospholipid plasma membrane: controls what enters and exits the cell

• Cytoplasm: mainly water, where most metabolism occurs

• DNA: genetic material

• Ribosomes: protein synthesis

What is the role of the cell wall in prokaryotes?

• Provides cell with strength and support

• Prevents cell from bursting

What is the role of the cytoplasm in prokaryotes?

• Metabolism

• Composed of water

What is the role of the plasma membrane in prokaryotes?

• Controls what enters/exists

• Composed of phospholipids

What is the role of 70S ribosomes in prokaryotes?

Protein synthesis

What is the role of the nucleoid region in prokaryotes?

• Contains single circular chromosome

• Contains DNA, genetic info for growth and development of the cell

What is the role of the flagellum in prokaryotes?

Locomotion

What is the role of the pilli in prokaryotes?

• Allow bacteria to adhere to each other and other surfaces

• Allow exchange of genetic material between bacteria

What is the role of the plasma membrane in eukaryotes?

• Controls what enters and exits the cell

• Composed of phospholipids

What is the role of the cytoplasm in eukaryotes?

• Metabolism

• Composed of water

What is the role of 80S ribosomes in eukaryotes?

Protein synthesis

What is the role of the nucleus in eukaryotes?

• Stores chromosomes associated with histone proteins

• Chromosomes contain genetic info for growth and development of cell

• RNA required for translation produced within nucleus

• Double membrane with pores - allow mRNA to enter cytoplasm

What is the role of rough ER in eukaryotes?

• Membrane structure with ribosomes attached

• Site of protein synthesis → transported to golgi apparatus

What is the role of smooth ER in eukaryotes?

• Lipid synthesis

• Detoxification

What is the role of the golgi apparatus in eukaryotes?

• Receives proteins from rough ER

• Modifies and packages proteins in vesicles for secretion

What is the role of chromosomes in eukaryotes?

• Composed of DNA wrapped around histone proteins

• Contain genetic info for growth and development of cell

What is the role of mitochondrion in eukaryotes?

Produce ATP by aerobic respiration

What is the role of vacuoles in eukaryotes?

• Store nutrients and wastes

• Maintain turgor pressure/water balance

What is the role of lysosomes in eukaryotes?

• Specialised vesicles which contain enzymes

• Digest large molecules

What is the role of the cell wall in eukaryotes?

• Made of cellulose

• Maintains cell shape

• Barrier against pathogens

What are the differences between prokaryotic and eukaryotic cells?

Eukaryotes have:

• Membrane bound organelles and mitochondria

• Many chromosomes in the nucleus

• Linear DNA wrapped around histone proteins

• Large 80S ribosomes

• Cell walls made of cellulose (plant) and chitin (fungi)

Prokaryotes have:

• No membrane bound organelles and mitochondria

• One chromosome in the nucleoid region in the cytoplasm

• DNA in a loop

• Small 70S ribosomes

• Cell walls composed of peptidoglycan

What are the processes of life carried out by all organisms?

• Metabolism

• Reproduction

• Homeostasis

• Growth

• Response to stimuli

• Excretion

• Nutrition

What is homeostasis?

Maintenance of internal conditions within a narrow range

What is metabolism?

Complex network of interdependent and interacting chemical reactions occurring in living organisms

What is nutrition?

Processes that organisms use to obtain and use food (nutrients) for growth and development

What is movement?

Changing position of the organism

What is excretion?

Removal of metabolic waste

What is growth?

Increase in mass/size of an organism

What is response?

Ability of organisms to respond to internal/external stimuli

What is reproduction?

Production of offspring

What are the differences between animal, fungi and plant cells?

Animal:

• No cell wall

• Small scattered vacuoles involved in storing materials and waste products

• Centrioles present - involved in mitosis and meiosis

• Plastids not present

• Cilia and flagella present in some

Fungi:

• Chitin cell walls

• Small/large vacuoles

• Centrioles, plastids, cilia and flagella not present

Plant:

• Cellulose cell walls

• Large central vacuole - store nutrients and waste, maintain turgor pressure

• Centrioles, cilia and flagella not present

• Plastids present e.g. chloroplasts

What are some atypical cell structures in eukaryotes?

• Aseptate fungal hyphae: multinucleated

• Skeletal muscle cells/muscle fibres: multinucleated

• Red blood cells: no nucleus

• Phloem sieve tube: no nucleus

What are the characteristics of prokaryotes on a micrograph?

• Small

• Nucleoid - lighter, irregularly-shaped region within cytoplasm

• No nucleus

• 70S ribosomes

• Cell wall

What are the characteristics of eukaryotes on a micrograph?

• Double membrane nucleus with pores

• Rough ER

• Smooth ER

Plants only:

• Chloroplast with many membranes

• Very large sap vacuole

What is the role of chloroplasts in eukaryotes?

• Contain chlorophyll

• Carry out photosynthesis for plants

What is the role of secretory vesicles in eukaryotes?

Transport proteins from golgi apparatus to plasma membrane to be secreted by exocytosis

What is the role of microvilli in eukaryotes?

• Increase surface area of cell

• Increase available surface area for transport of materials