2.1.1 Cell strucutre

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49 Terms

1
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What are the different elements of a eukaryotic cell (12)

  • Cell wall

  • Cell membrane

  • Nucleus

  • Mitochondria

  • Chloroplast

  • Ribosomes

  • Rough endoplasmic reticulum (RER)

  • Smooth endoplasmic reticulum (SER)

  • Golgi apparatus (Golgi complex)

  • Vesicles

  • Vacuole

  • Lysosome

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What is the structure and purpose of the cell membrane

  • Controls the exchange of materials between the internal cell environment and the external cell environment

  • Partially permeable

  • Fluid - constantly in motion

    • Due to the 2 layers of fat constantly attracting and repelling each other

  • Primarily made up of phospholipids

<ul><li><p>Controls the exchange of materials between the internal cell environment and the external cell environment</p></li><li><p>Partially permeable</p></li><li><p>Fluid - constantly in motion</p><ul><li><p>Due to the 2 layers of fat constantly attracting and repelling each other</p></li></ul></li><li><p>Primarily made up of <span style="color: yellow">phospholipids</span></p></li></ul>
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What is the structure and purpose of the cell wall

  • Provides structural support to the cell

  • Made up of polysaccharides (type of carbohydrate)

    • Cellulose in plants

    • Peptidoglycan in most bacterial cells

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What is the structure and purpose of the nucleus

  • Contains chromatin (linear DNA bound to histone proteins)

  • Separated from the cytoplasm by a double membrane which is full of pores

    • allows MRNA & ribosomes to leave the nucleus and enzymes

  • Contains Nucleolus - site of ribosome production, some cells have multiple nucleoli

<ul><li><p>Contains chromatin (linear DNA bound to histone proteins)</p></li><li><p>Separated from the cytoplasm by a double membrane which is full of pores</p><ul><li><p>allows MRNA &amp; ribosomes to leave the nucleus and enzymes</p></li></ul></li><li><p><span style="color: yellow">Contains Nucleolus</span> - site of ribosome production, some cells have multiple nucleoli</p></li></ul>
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What are histone proteins

Condenses DNA into chromosomes

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What is the structure and purpose of mitochondria

  • Site of aerobic respiration

  • Surrounded by a double membrane

    • Inner membrane folds in on itself to form a cristae - this increases it surface area

  • The cristae forms the matrix, where many enzymes that are needed for respiration can be found

  • Smaller, circular mitochondrial DNA (mtDNA) and ribosomes are also found here

    • They need their own to supply themselves to deal with their ‘high work load’

  • Can vary in shape and size

<ul><li><p>Site of aerobic respiration</p></li><li><p>Surrounded by a double membrane</p><ul><li><p>Inner membrane folds in on itself to form a <span style="color: yellow">cristae</span> - this increases it surface area</p></li></ul></li><li><p>The cristae forms the <span style="color: yellow">matrix</span>, where many enzymes that are needed for respiration can be found</p></li><li><p>Smaller, circular mitochondrial DNA (mtDNA) and ribosomes are also found here</p><ul><li><p>They need their own to supply themselves to deal with their ‘high work load’</p></li></ul></li><li><p>Can vary in shape and size </p></li></ul>
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What is the structure and purpose of the chloroplast

Site of photosynthesis

  • Light dependent phase: Takes place in thylakoids - which stack to form granum

  • The light independent phase (Calvin cycle): Takes place in the stomata

  • Surrounded by a double membrane

  • Also contain small, circular DNA and ribosomes

<p>Site of photosynthesis</p><ul><li><p><strong>Light dependent phase:</strong> Takes place in <span style="color: yellow">thylakoids</span> - which stack to form <span style="color: yellow">granum</span> </p></li><li><p><strong>The light independent phase </strong>(Calvin cycle): Takes place in the stomata</p></li><li><p>Surrounded by a double membrane</p></li><li><p>Also contain small, circular DNA and ribosomes </p></li></ul>
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How are lamella built

  • Thylakoids (containing chlorophyll) stack to form a granum (grana) - to increase its surface area

  • Grana stack to form a lamella (lamella)

<ul><li><p>Thylakoids (containing chlorophyll) stack to form a granum (grana) - to increase its surface area</p></li><li><p>Grana stack to form a lamella (lamella)</p></li></ul>
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What is the structure and purpose of ribosomes

  • Found freely in the cytoplasm of all cells or as part of the rough endoplasmic reticulum (RER)

  • Site of translation - protein synthesis

  • Each ribosome is a complex of ribosomal RNA (rRNA) and proteins

  • Eukaryotes have larger ribosomes due to being larger + making larger proteins

    • Eukaryotic cells contain 80s ribosomes

    • Prokaryotes, mitochondria and chloroplasts contain 70s ribosomes

    • (‘S’ stands for a unit of measurement)

<ul><li><p>Found freely in the cytoplasm of all cells or as part of the <span style="color: yellow">rough endoplasmic reticulum</span> (RER)</p></li><li><p>Site of translation - protein synthesis </p></li><li><p>Each ribosome is a complex of ribosomal RNA (rRNA) and proteins</p></li><li><p>Eukaryotes have larger ribosomes due to being larger + making larger proteins</p><ul><li><p>Eukaryotic cells contain 80s ribosomes</p></li><li><p>Prokaryotes, mitochondria and chloroplasts contain 70s ribosomes</p></li><li><p>(‘S’ stands for a unit of measurement)</p></li></ul></li></ul>
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What is the structure and purpose of the Rough endoplasmic reticulum (RER)

  • Where protein is ‘edited’

  • Surface covered in ribosomes

  • Formed from continuous folds of membrane that is attracted to the nuclear envelope

  • Process proteins made by the ribosomes

<ul><li><p>Where protein is ‘edited’</p></li><li><p>Surface covered in ribosomes</p></li><li><p>Formed from continuous folds of membrane that is attracted to the nuclear envelope</p></li><li><p>Process proteins made by the <span style="color: yellow">ribosomes</span></p></li></ul>
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What is the structure and purpose of the Smooth endoplasmic reticulum (SER)

  • Does not have ribosomes on the surface

  • Involved in the production, processing and storage of lipids, carbohydrates and steroids

<ul><li><p>Does not have ribosomes on the surface</p></li><li><p>Involved in the production, processing and storage of lipids, carbohydrates and steroids</p></li></ul>
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What is the structure and purpose of the Golgi apparatus (Golgi complex)

  • Flattened sacs of membranes

  • Responsible for modifying proteins and lipids

    • Pack them into Golgi vesicles

      • Vesicles transport proteins and lipids to their destination

  • Proteins that go through the Golgi apparatus are usually exported, put into lysosomes or delivered to membrane-bound organelles

  • Proteins enter through a vesicle on the cis face (side) and exists through a vesicle on the trans face

<ul><li><p>Flattened sacs of membranes</p></li><li><p>Responsible for modifying proteins and lipids</p><ul><li><p>Pack them into <span style="color: yellow">Golgi vesicles</span></p><ul><li><p>Vesicles transport proteins and lipids to their destination</p></li></ul></li></ul></li><li><p>Proteins that go through the Golgi apparatus are usually exported, put into <span style="color: yellow">lysosomes</span> or <span style="color: yellow">delivered to membrane-bound organelles</span></p></li><li><p>Proteins enter through a vesicle on the cis face (side) and exists through a vesicle on the trans face</p><p></p></li></ul>
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What is the purpose of vesicles

Membrane - bound sacs for transports & storage

<p>Membrane - bound sacs for transports &amp; storage</p>
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What is the structure and purpose of large permanent vacuoles

  • Sacs in plant cells surrounded by the tonoplast - a selectively permeable membrane

  • Helps maintain tugor pressure

  • Stores water, salts, minerals, pigments & proteins within a cell

<ul><li><p>Sacs in plant cells surrounded by the <span style="color: yellow">tonoplast</span> - a selectively permeable membrane</p></li><li><p>Helps maintain tugor pressure</p></li><li><p>Stores water, salts, minerals, pigments &amp; proteins within a cell</p></li></ul>
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What is the structure and purpose of a lysosome

  • Specialist forms of vesicles which contain hydrolytic enzymes (enzymes that break down biological molecules)

  • The enzymes break down waste materials such as worn-out organelles

  • Cells of the immune system & cells involved in apoptosis (when the cell is instructed to kill itself) use lysosomes a lot

<ul><li><p>Specialist forms of vesicles which contain hydrolytic enzymes (enzymes that break down biological molecules)</p></li><li><p>The enzymes break down waste materials such as worn-out organelles</p></li><li><p>Cells of the immune system &amp; cells involved in apoptosis (when the cell is instructed to kill itself) use lysosomes a lot</p></li></ul>
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What is the purpose of a microvilli

Cell membrane projections that increase the surface area for absorption

<p>Cell membrane projections that increase the surface area for absorption</p>
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What is the structure and purpose of the cilia

  • Hair like projections made form micro tubules

  • Allows the movement of substances over the cell surface

<ul><li><p>Hair like projections made form micro tubules </p></li><li><p>Allows the movement of substances over the cell surface </p></li></ul>
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What is the structure of flagella

Similar to cilia in structure but made of larger micro-tubules

<p>Similar to cilia in structure but made of larger micro-tubules</p>
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What are the different elements of prokaryotic cells (10)

  • Flagellum - sometimes present

  • Capsule - sometimes present

  • In folding of cell surface membrane - sometimes present

  • Plasmid - sometimes present

  • Pili - sometimes present

  • Cell wall

  • Cell membrane

  • Cytoplasm

  • Circular DNA

  • Ribosomes

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What are the structures unique to prokaryotic cells

  • Plasmids

  • Capsule

  • Flagellum

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What is the structure and purpose of plasmids

  • Small loops of DNA that are separate from the main circular DNA molecule

  • Contains DNA that can be passed between prokaryotes

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What is the structure and purpose of capsules

Helps protect bacteria from drying out and from attack from by cells from the hosts immune system

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What is the structure and purpose of the flagellum

  • Long, hair like structure that rotates, enabling movement

  • Some have more then 1

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What is the purpose of the infolding of the cell membrane

  • May allow for photosynthesis

  • May carry out nitrogen fixation

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What is the purpose of the pili

  • For attachement to other cells or surfaces

  • Involved in sexual reproduction

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Prokaryotes vs Eukaryotes

  • Prokaryotes are 100-1000 x smaller

  • Cytoplasm lacks membrane-bound organelles

  • Smaller ribosomes (70s)

  • No nucleus, no histone proteins - free floating DNA

  • Cell wall made up of peptidoglycan & murein

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What is magnification

How many times bigger the image produced by the microscope is, compared to the real object under the microscope

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What is resolution

The ability to distinguish between objects that are close together

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What are the two main types of microscopes

  • Optical (or light)

  • Electron

    • Transmission electron microscopes (TEMs)

    • Scanning electron microscopes (SEMs)

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How is total magnification calculated

Eyepiece lens magnification x objective lens magnification

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Optical light microscopes fact file

  • Maximum resolution: ~ 0.2 micrometers

  • Maximum magnification: x1500

  • Structures you can visualise: eukaryotic cells, nuclei, (sometimes) mitochondria and chloroplast

  • Advantages:

    • Inexpensive

    • small and portable

    • simple slide preparation (doesn’t usually distort sample)

    • specimens can be living or dead

    • Produced a coloured image

  • Disadvantages:

    • Lower magnification then electron microscopes

    • Lower resolving power then electron microscopes (200nm)

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How do transmission electron microscopes work

  • Use electromagnets to focus a beam of electrons which is then transmitted through the specimen

  • Denser parts of specimen absorb more electrons so appear darker

  • In black and white as they don’t absorb light

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What are the advantages of transmission electron microscopes

  • High resolution images

  • Allows the internal structures within cells & organelles to be seen

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What are the disadvantages of transmission electron microscopes

  • Only to be used with very thin specimens/thin sections

  • Can’t be used to observe live specimens

  • Specimens take time to prepare which increases the chance of artefacts being produced

    • Artefacts - something not part of the organism e.g dust, air particles

  • Do not produce a colourful image

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How do scanning emission microscopes work

  • They scan a beam of electrons across the specimen

    • Beam bounces off the surface of the specimen

      • Electrons are detected

        • Forms an image

  • Produce 3D images that show the surface of specimens

<ul><li><p>They scan a beam of electrons across the specimen</p><ul><li><p>Beam bounces off the surface of the specimen</p><ul><li><p>Electrons are detected</p><ul><li><p>Forms an image</p></li></ul></li></ul></li></ul></li><li><p>Produce 3D images that show the surface of specimens</p></li></ul><p></p>
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What are the advantages of scanning emission microscopes

  • Can be used on thick or 3D structures

  • Allows the external 3D structure to be observed

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What are the disadvantages of scanning emission microscopes

  • Give a lower resolution images then TEMs

  • Can’t be used to observe live specimens

  • Do not produce a coloured image

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Election microscopes fact file

  • Maximum resolution: 0.2 nm

  • Maximum magnification: ~ x 1,500,00

  • Structures you can visualise: small organelles - ribosomes, endoplasmic reticulum, lysosomes

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What are the light microscope sample preparation methods

  • Dry mount

  • Wet mount

  • Squash slides

  • Smear slides

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How does a dry mount work

  • Solid specimens

  • Viewed whole or sectioned

  • Specimen placed in the centre of the slide

  • Coverslip placed on top

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How does a wet mount work

  • Specimens are suspended in a liquid (oil or water) and a cover slip is placed on top from an angle

  • Can be used for aquatic samples or other living organisms

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How do squash slides work

  • Used for soft samples e.g. root tips - to look at cell division

  • A wet mount is prepared

  • The cover slip is gently pressed down upon

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How do smear slides work

  • Sample is smeared by the edge of a slide to create a thin even coating/ layer

  • The coverslip is then placed on top

  • Used with blood

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How is staining used with light microscopes

  • To prepare a sample for staining:

    • Placed on slide

    • Allowed to air dry

    • Heat fixed by passing through a flame

    • Specimen will adhere to slide and will then take up stains

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Why is staining used with light microscopes

  • Stains are used to increase contrast as different components within a cell take up stains to different degrees

  • Increase in contrast allows components to become visible so they can be identified

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How are samples prepared in electron microscopes

  • Samples must be prepared in a specific way due to the vacuums inside the microscope

  • Specimens must be fixated using chemicals or freezing, staining with heavy metals and dehydration with solvents

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What is differential staining

  • Helps distinguish between different organisms or between organelles in a tissue sample

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What is Gram staining

  • Uses crystal violet and iodine to help divide bacteria into gram positive (charge) and gram negative groups (charge)

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What is acid fast staining

  • Differential staining used to identify acid fast organisms (micro organisms with highly impermeable cell walls)