2.1- Cell Structure Flashcards by Caitlin Peploe

Define 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 & arachaea

How well did you know this?

Not at all

Perfectly

State relationship between a system and specialised cells

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

How well did you know this?

Not at all

Perfectly

Describe structure and function of cell-surface membrane

‘Fluid mosaic’ phospholipid bilayer with extrinsic & intrinsic proteins embedded
- Isolates cytoplasm from extracellular environment
- Selectively permeable to regulate transport of substances
- Involved in cell signalling / cell recognition

How well did you know this?

Not at all

Perfectly

Explain role of cholestreol, glycoproteins & glycolipids in cell-surface membrane

Cholesterol: Steroid muscle connects phospholipids & reduces fluidity
Glycoproteins: cell signalling, cell recognition (antigens) & binding cells together
Glycolipids: cell signalling & cell recognition

How well did you know this?

Not at all

Perfectly

Describe structure of the nucleus

Surrounded by nuclear envelope, a semi-permeable double membrane
Nuclear pores all substances to enter/exit
Dense nucleolus made of RNA & proteins assembles ribosomes

How well did you know this?

Not at all

Perfectly

Describe function of the nucleus

Contains DNA coiled around chromatin into chromosomes
Controls cellular processes: gene expression determines specialisation & site of mRNA transcription, mitosis, semi conservative replication

How well did you know this?

Not at all

Perfectly

Describe 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

How well did you know this?

Not at all

Perfectly

Describe structure of a chloroplast

Vesicular plastid with double membrane
Thylakoids: flattened discs stack to form grana; contain photosystems with chlorophyll
Intergranal lamellae: tubes attach thylakoids in adjacent grana
Stroma: fluid-filled matrix

How well did you know this?

Not at all

Perfectly

State function of mitochondria

Site of aerobic respiration to produce ATP

How well did you know this?

Not at all

Perfectly

State function of chloroplast

Site of photosynthesis to convert solar energy to chemical energy

How well did you know this?

Not at all

Perfectly

Describe structure and function of Golgi Body

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 & packages proteins for export
- synthesises glycoproteins

How well did you know this?

Not at all

Perfectly

Describe structure and function of a lysosome

Sac surrounded by single membrane embedded H+ pump maintains acidic conditions contains digestive hydrolase enxymes
glycoprotein coat protects cell interior:
- digests contents of phagosome
- exocytosis of digestive enzymes

How well did you know this?

Not at all

Perfectly

Describe structure and function of a ribosome

Formed of protein & rRNA
free in cytoplasm or attached to ER
- Site of protein synthesis via translation:
large subunit: joins amino acids
small subunit: contains mRNA binding site

How well did you know this?

Not at all

Perfectly

Describe structure and function of the endoplasmic reticulum (ER)

Cisternae: network of tubules & flattened sacs extends from cell membrane through cytoplasm & connects to nuclear envelope:
- Rough ER: many ribosomes attached for protein synthesis and transport
- Smooth ER: lipid synthesis

How well did you know this?

Not at all

Perfectly

Describe structure of cell wall

Bacteria: made of polysaccharide murein
Plants: -
made of cellulose microfibrils
- plasmodesmata allow molecules to pass between cells
- middle lamella acts as boundary between adjacent cell walls

How well did you know this?

Not at all

Perfectly

State functions of the cell wall

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

How well did you know this?

Not at all

Perfectly

Describe structure and function of vacuole in plants

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

Contains turgor pressure
Absorbs and hydrolyses potentially harmful substances to detoxify cytoplasm

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 role of plasmids in prokaryotes

Small ring of DNA that carries non-essential genes
Can be exchanged between bacterial cells via conjugation

State role of flagella in prokaryotes

Rotating tail propels (usually unicellular) organism

State the role of capsule in prokaryotes

Polysaccharide layer:
- Prevents desiccation
- Acts as food reserve
- Provides mechanical protection against phagocytosis & external chemicals
- Stick cells together

Compare eukaryotic and prokaryotic cells

Both have:
- cell membrane
- cytoplasm
- ribosomes (don’t count as organelle as not membrane-bound)

Contrast eukaryotic and prokaryotic cells

Prokaryotic:
- small cells & always unicellular
- non membrane-bound organelles & no nucleus
- circular DNA not associated with proteins
- small ribsosomes (70S)
- binary fission- always asexual reproduction
- murein cell walls
- capsule, sometimes plasmids & cytoskeleton

Eukaryotic:
-larger cells & often multicellular
- always have organelles & nucleus
- linear chromosomes associated with histones
- larger ribosomes (80S)
- mitosis & meisosis- sexual and/or asexual
-cellulose cell wall (plants)/ chitin (fungi)
- no capsule, no plasmids, always cytoskeleton

Why are viruses referred to as particles instead of cells?

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

Describe structure of a viral particle

- Linear genertic material (DNA or RNA) & viral enzymes e.g. reverse transcriptase. - Surrounded by capsid (protein coat made of capsomeres) - No cytoplasm

Describe structure of an enveloped virus

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

State role of capsids on viral particles

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

State role of attachment proteins on viral particles

Enable viral particle to bind to complementary sits on host 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 wavelengths 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 degrees to avoid trapping air bubbles

Suggest advantages and limitations of an optical microscope

+ colour image + can show living structures + affordable apparatus - 2D image - lower resolution than electron microscope = cannot see ultrastructure

Describe how a transmission electron microscope (TEM) works

1. Pass a high energy beam of electrons through a thin slice of specimen 2. More dense structures appear darker since they absorb more electrons 3. Focus image onto fluorescent screen or photographic plate using magnetic lenses

Suggest the advantages and limitations of using a TEM

+ electrons have shorter wavelength than light= high resolution, so ultrastructure visible + high magnification (x500000) - 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 specimen's surface using electromagnetic lenses 2. Reflected lenses 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

Factor by which the image is larger than the actual specimen

Define 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 micrometers on the micrometer. 3. Length of 1 eyepiece division = 100 micrometer/ number of divisions 4. Use calibrated values to calculate actual length of structures

Calculation for actual size from microscopy

Actual size = image size/magnification

Outline what happens during cell fractionation and ultracentrifugation

1. Mince and homogenise tissue to break open cells & release organelles 2. Filter homogenate to remove debris 3. Perform differential centrifugation: a) Spin homogenate in centrifuge b) The most dense organelles in mixture will form a pellet c) Filter off the supernatant and spin again at a higher speed

State order of sedimentation of organelles during differential centrifugation

most dense -> least dense nucleus -> mitochondria -> lysosomes -> RER -> plasma membrane -> SER -> ribosomes

Explain why fractionated 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