2.1 Cell Structure Flashcards by Ibrahim Uddin

Define the terms eukaryotic and prokaryotic cell

Eukaryotic: DNA is contained in a nucleus, contains membrane-bound specialised organelles

Prokaryotic: DNA is ‘free’ in cytoplasm, no organelles e.g. bacteria and archea

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State the relationship between a system and specialised cells

Specialised cells —> tissues that perform specific function —> organs made of several tissue types —> organ systems

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Describe the structure and function of the cell-surface membrane

‘Fluid mosaic’ phospholipid bilayer with extrinsic and intrinsic proteins embedded

Isolates cytoplasm from extracellular environment
Selectively permeable to regulate transport of substances
involved in cell signalling/cell recognition

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Explain the role of cholesterol, glycoproteins and glycolipds in the cell surface membrane

Cholesterol: steroid molecule connects phospholipids and reduces fluidity

Glycoproteins: cell signalling, cell recognition (antigens) and binding cells together

Glycolipds: cell signalling and cell recognition

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Describe the structure of the nucleus

Surrounded by nuclear envelope, a semi-permeable double membrane

Nuclear pores allow substances to enter/exit

Dense nucleolus made of RNA and proteins assembles ribosomes

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Describe the function of the nucleus

Contains DNA coiled around chromatin into chromosomes

Controls cellular processes: gene expression determines specialisation and site of mRNA transcription, mitosis,semi conservative replication

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Describe the structure of a mitochondrion

Surrounded by double membrane, folded inner membrane forms Cristae: site of electron transport chain

Fluid matrix: contains mitochondrial DNA,respiratory enzymes, lipids, proteins

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Describe the structure of a chloroplast

Vesicular plastid with double membrane

Thylakoids: flattened discs stack to form grana; contain photosystems with chlorophyll

Intergranal lamellae: tubes attached to thylakoids in adjacent grana

Stroma: fluid-filled matrix

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State the function of mitochondria and chloroplasts

Mitochondria: site of aerobic respiration to produce ATP

Chloroplasts: site of photosynthesis to convert solar energy to chemical energy

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Describe the structure and function of the Golgi apparatus

Planar stack of membrane-bound, flattened sacs cis face aligns with rER
Molecules are processed in cisternae vesicles bud off trans face via exocytosis:

Modifies and packages proteins for export
Synthesises glycoproteins

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Describe the structure and function of a lysosome

sac surrounded by single membrane

Contains a embedded H+ pump which maintains acidic conditions and digestive hydrolase enzymes.
glycoproteins coat protects cell interior:

Digests contents of phagosome
Exocytosis of digestive enzymes

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Describe the structure and function of a ribosome

Made up of protein and rRNA
Can be found free in cytoplasm or attached to ER

Site of protein synthesis via translation
Large subunit: joins amino acids
Small subunit: contains mRNA binding site

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Describe the structure and function of the endoplasmic reticulum (ER)

Cisternae: a network of tubules and flattened sacs extends from the cell membrane through cytoplasm and connects to nuclear envelope

Rough ER: many ribosome attached for protein synthesis and transport

Smooth ER: lipid synthesis’s

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Describe the structure of the cell wall in plants and bacteria

Bacteria: made of polysaccharide murein

Plants: made of cellulose microfibrils
Plasmodesmata allow molecules to pass between cells, middle lamellla acts as boundary between adjacent cell walls

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State the function of the cell wall

Mechanical strength and support
Physical barrier against pathogens
Part of apoplast pathway (plants) to enable easy diffusion of water

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Describe the structure and function of the cell vacuole in plants

Surrounded by single membrane: tonoplast contains cell sap: mineral ions, water, enzymes, soluble pigments

Controls turgor pressure
Absorbs and hydrolyses potentially harmful substances to detoxify the cytoplasm

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Explain some common cell adaptations

Folded membrane or microvilli increase surface area e.g. for diffusion

Many mitochondria = large amounts of ATP for active transport

Walls one cell thick to reduce distance of diffusion pathway

State the role of plasmids in prokaryotes

Small ring of DNA that carries non-essential genes

Can be exchanged between bacterial cells via conjugation

State the role of flagella in prokaryotes

Rotating tail propels (usually unicellular) organism

State the role of the capsule in prokaryotes

A capsule is a polysaccharide layer that

Prevents desiccation
Acts as food reserve
Provides mechanical protection against phagocytosis and external chemicals
Sticks cells together

Compare eukaryotic and prokaryotic cells

Both have:

Cell membrane
Cytoplasm
Ribosome

Contrast eukaryotic and prokaryotic cells

Eukaryotic

larger cells and often multicellular
always have organelles and nucleus
Linear chromosomes associated with histones

Prokaryotic

small cells and always unicellular
no membrane-bound organelles and no nucleus
circular DNA not associated with proteins

Why are viruses referred to as ‘particles’ instead of cells

Acellular and non living: no cytoplasm, cannot self-reproduce, no metabolism

Describe the structure of a viral particle

Linear genetic material(DNA OR RNA) and viral enzymes e.g. reverse transcriptase
Surrounded by capsid (protein coat made of capsomeres)
No cytoplasm

Describe the structure of an enveloped virus

Simple virus surrounded by matrix protein. Matrix protein surrounded by envelop derived from cell membrane of host cell Attachment proteins on surface

State the role of the capsid on viral particles

Protect nucleic acid from degradation by restriction endonucleases Surface sites enable viral particle to bind to and enter host cells or inject their genetic material

State the role of attachment proteins on viral particles

Enable viral particle to bind to complementary sites on his cell : entry via endosymbiosis

Describe how optical microscopes work

1. Lenses focus rays of light and magnify the view of a thin slice of specimen 2. Different structures absorb different amounts and wavelength of light 3. Reflected light is transmitted to the observer via the objective lens and eyepiece

Outline how a student could prepare a temporary mount of tissue for an optical microscope

1. Obtain thin section of tissue e.g. using ultratome or by maceration 2. Place plant tissue in a drop of water 3. Stain tissue on a slide to make structures visible 4. Add coverslip using mounted needle at 45 degree to avoid trapping air bubbles

Suggest the advantages and limitations of using an optical microscope

``` + colour image + can show living structures + affordable apparatus -2D image -lower resolution than electron microscopes = cannot see ultra structure ```

Describe how a transmission electron microscope (TEM) works

Passes a high energy beam of electrons through thin slice of specimen More dense structures appear darker since they absorb more electrons. Focus image onto fluorescent screen or photographic plate using magnetic lenses

Suggest the advantages and limitations of using a TEM

+ electrons have shorter wave length than light = high resolution so ultrastructure visible +high magnification (X5000000) -2D image -requires a vacuum = cannot show living structures -extensive preparation may introduce artefacts No colour image

Describe how a scanning electron microscope (SEM) works

1. Focus a beam of electrons onto a specimens surface using electromagnetic lenses 2. reflected electrons hit a collecting device and are amplified to produce an image on a photographic plate

Suggest the advantages and limitations of using an SEM

+3D image +electrons have shorter wavelength than light = high resolution -requires a vacuum = cannot show living structures -no colour image -only shows outer surface

Define magnification and resolution

Magnification: factor by which the image is larger than the actual specimen Resolution: smallest separation distance at which 2 separate structures can be distinguished from one another

Explain how to use an eyepiece graticule and stage micrometer to measure the size of a structure

1. Place micrometer on stage to calibrate eyepiece graticule 2. Line up scales on graticule and micrometer. Count how many graticule divisions are in 100 micro meters on the micrometer 3. length of 1 eyepiece division = 100 micrometer / number of Divisions 4. use calibrated values to calculate actual length of structures

State an equation to calculate the actual size of a structure from microscopy

Image size = actual size X magnification

Outline what happens during cell fractionation and ultracentrifugation

1. Mince and homogenize tissue to break open cells and release organelles 2. Filter homogenate to remove debris 3.perform differential centrifugation A)spin homogenate B)the most dense organelles in the mixture form a pellet C)filter off the supernatent and spin again at a higher speed

State the order of sedimentation of organelles during differential centrifugation

Most dense —> least dense Nucleus—>mitochondria —>lysosome —>RER —>plasma membrane —>SER —>ribosomes

Explain why fractionation cells are kept in a cold,buffered,isotonic solution

Cold: slow action of hydrolase enzymes Buffered: maintain constant pH Isotonic: prevent osmotic lysis/shrinking of organelles