cell structure Flashcards

Question

features of both EM

Answer 1

Are large and very expensive Need a great deal of skill and training to use

Answer 2

determined by the wavelength of light

Answer 3

determined by the wavelength of the beam of electrons

Answer 4

Magnification refers to how many times larger the image is compared to the object Magnification = image size/object size

Answer 5

Artefacts are false visible details that aren't part of the specimen being observed, such as air bubbles or fingerprints.

Answer 6

Caused by: Treatment process Creation of sample Dehydration staining/addition of heavy metals

Answer 7

Dehydrating the specimens Samples need to be preserved with chemicals such as formaldehyde Water is removed and replaced with wax/resin plastic to retain shape and longevity Embedding them in wax to prevent distortion during slicing Using a special instrument to make very thin slices called sections - to allow light to pass through - these are stained and mounted in a special chemical to preserve them

Answer 8

1) Dry mount 2) Wet mount 3) Squash slide 4) Smear slide

Answer 9

when thin slices or whole specimens are viewed, with just the coverslip place on top eg/ plant tissue or hair

Answer 10

when the specimens are added to water or a stain before you have the coverslip lowered on top with a mounted needle to prevent air bubbles from forming - aquatic organisms could be viewed this way

Answer 11

wet mounts which you then push down on the coverslip to squash the sample to ensure you have a thin layer of cells to enable light to pass through - used when creating a root tip squash sample to view the chromosomes in mitosis

Answer 12

created by placing a drop of the sample at one end of the slide and using the edge of another slide (held at an angle) to smear the sample across the first slide to create a smooth, thin, even coated specimen - cover slip is placed on top after smearing - used when examining blood cells in a blood sample

Answer 13

Stains are coloured chemicals that bind to molecules in or on the specimen making the specimen easy to use Stains can be used for many purposes

Answer 14

Charge attraction (eg/ methylene blue - positively charged binds to negatively charged materials at cells Charge repulsion Structural difference Gram positive - crystal violet Gram negative - safranin dye Methylene blue is an all-purpose stain Some cell components and cells are difficult to see unless they are stained a more obvious colour

Answer 15

technique which involves many chemical stains being used to stain different parts of a cell in different colours - bind to specific cell structures- makes it visually obvious what your looking at

Answer 16

Inside light microscope , in the eye piece there is actually a scale that you can insert on a glass disc which is called the eyepiece graticule

Answer 17

You can use this scale to measure the size of the object your looing at but there are different lenses on your microscope which are going to be causing different magnifications At each magnification, the value of one of the divisions on your your eyepiece graticule will be different so you have to know how to calibrate it at every magnification Each time you change the objective lens and the magnification, you have to calibrate the eyepiece and work out what each eye piece unit is worth

Answer 18

In order to calibrate the eyepiece graticule you need a stage micrometer which is a glass slide which has a ruler on it You would place it on the stage of your microscope and then look through your eyepiece and then move your stage micrometer so that it is aligned right next to your eyepiece graticule Bottom scale is the scale on your stage micrometer and that has been aligned with your eyepiece graticule Once you've got them aligned, count how many divisions on the eyepiece graticule fit into one division on the micrometer scale Each division on the micromete is 10mcrometers so this can be used to calculate what one division on the eyepiece graticule is at that current magnification The stage graticule will correspond to a number of eyepiece divisions The stage graticule is 1mm or 1000 micrometers Each eyepiece division will be 1000/number micrometers

Answer 19

animals,plants and fungi

Answer 20

archaea and bacteria

Answer 21

In all eukaryotic cells, the DNA is contained in a membrane-bound nucleus Membrane-bound - means surrounded by a membrane Nucleus actually have a double membrane Some eukaryotic cells can lose their nucleus as they develop, for example red blood cells in humans but vast majority of eukaryotic cells have a nucleus throughout their lifespan Second key feature of eukaryotic cells is that their DNA is tightly wrapped around proteins called histones Together the DNA and histone proteins form chromosomes By tightly coiling their DNA into chromosomes, eukaryotic cells can pack a great deal of DNA into their nucleus Another key feature of eukaryotes is that their DNA is a linear molecule The word linear means that the ends of the DNA molecule in a chromosome are not joined together to form a loop

Answer 22

Membrane-bound organelles are present in eukaryotes - eg/ golgi apparatus, mitochondria, cytoplasm, endoplasmic reticulum

Answer 23

Eukaryotic cells also contain other organelles that are not membrane-bound Eg - ribosomes which are involved in protein synthesis Ribosomes in eukaryotic cells are larger than those in prokaryotes - eukaryotic cells contain 80S ribosomes

Answer 24

S - unity showing how quickly organelles move in a centrifuge

Answer 25

Eukaryotic cells are surrounded by a cell-surface membrane which helps to control the molecules that can pass in and out of the cell

Answer 26

In plants and fungi, the cell membrane is surrounded by a cell wall - cell wall helps to maintain the structure of these cells

Answer 27

polysaccharide cellulose

Answer 28

polysaccharide chitin

Answer 29

rokaryotic cells are much smaller than eukaryotic cells Have no membrane bound organelles at all This means that in prokaryotic cells, DNA is found in the cytoplasm rather than in a nucleus In prokaryotic cells, DNA is arranged into a circular chromosome with no free ends DNA in prokaryotes is not bound to histone proteins Bacterial cells contain small loops of DNA called plasmids

Answer 30

Plasmids usually contain a relatively small number of genes - but these can include genes which make the bacterium resistant to antibiotics so plasmids are very important for bacteria Eukaryotic cells do not contain plasmids

Answer 31

Ribosomes in prokaryotic cells are smaller than in eukaryotic cells - have a size of 70S whereas eukaryotic ribosomes have a size of 80S

Answer 32

Prokaryotic cells such as bacteria are surrounded by a cell wall - in bacteria, this is made from peptidoglycan which is also called murein Peptidoglycan - polymer formed between peptides and polysaccharide molecules Bacteria cell wall helps to maintain structure of the cell eg/ - if water moves into the bacterial cell by osmosis, cell wall prevents cell from bursting Some bacteria produce a slime capsule on the outside of hte cell wall - slime capsule can help to protect the bacteria from phagocytosis in WBCs Some have a flagellum which help them to move Prokaryotic flagellum has a different structure to that found in eukaryotes Some bacteria also have fine protein strands on their surface - these are called pili which help bacteria to attach to surfaces and also to attach to other bacteria When two bacteria are attached, DNA can be transferred from one bacterium to another Bacteria also contain lipid droplets and glycogen granules - act as nutrient stores for the bacterial cells Sometimes, using the electron microscope, we can see infoldings in the cell membrane of prokaryotic cells - these are called mesosomes Initially scientists though ribosomes played a role in respiration but they now believe that mesosomes are actually artefacts that are created when bacterial cells are prepared for electron microscopy

Answer 33

Enzymes are proteins Enzymes are required for all the chemical reactions taking place in cells Other proteins play a structural role in cells - for example, moving organelles to where they are needed Some proteins act as transport molecules - eg/ haemoglobin which transports oxygen in mammals

Answer 34

Protein synthesis is one of the most important functions taking place in cells Involves several different organelles The instructions for encoding the amino acid sequence of a protein are contained within the gene for that protein - these genes are part of the chromosomes which we find in the nucleus To synthesise a protein, the genetic information encoded by that gene is converted to messenger RNA or mRNA This process is called transcription This mRNA then leaves the nucleus Now a ribosome reads the information contained in the mRNA and synthesises the protein molecule - this is called translation If protein remains in cytoplasm , eg cellular enzyme, then translation will take places on a free ribosome in the cytoplasm However some proteins are secreted from cells - eg/ digestive enzymes and antibodies Secreted proteins are translated on a ribosome attached to RER These proteins then make their way through the rough ER and the golgi apparatus before leaving the cell

Answer 35

Has a nuclear envelope which is this double membrane layer and the holes that you can see within it are the nuclear pores and that is what the mRNA can pass out of after transcription Nucleoplasm - this granular, jelly like material in the middle Chromosomes - found inside of the nucleus, are protein bound so wrapped around histone proteins and they are linear Nucleolus - smaller sphere inside of the nucleus which is the site of rRNA production and makes ribosomes Nuclear envelope separates the contents of the nucleus from the rest of the cell In some regions outer and inner membranes fuse together - at some points, some dissolved substances and ribosomes can pass through Pores enable larger substance such as mRNA to leave the nucleus Substances such as steroid hormones may enter the nucleus from the cytoplasm via these pores Contains DNA wound into linear chromosomes

Answer 36

Nucleolus - smaller sphere inside of the nucleus which is the site of rRNA production and makes ribosomes Nucleolus region is where ribosomes are formed from rRNA and proteins including an enzymatic site of peptidyl transferase which catalyses the condensation reaction between amino acids to form peptide bonds Nucleolus does not have a membrane around it, contains RNA Chromatine is the genetic material - consisting of DNA wound around histone protein When cell is not dividing, chromatin is spread out or extended, when cell is about to divide, chromatin condenses and coils tightly into chromosomes

Answer 37

In summary, the nucleus: Control centre of the cell Stores the organism's genome Transmits genetic information Provides instructions for protein synthesis Function of nucleus Site of DNA replication and transcription ( first stage of protein synthesis when mRNA is created ) Contains the DNA for each cell Site of ribosome synthesis

Answer 38

Prokaryotic cell - no nucleus - instead of a nucleus there is a single circular DNA molecule free in the cytoplasm which is not protein bound (NOT ATTACHED TO PROTEINS) Contains DNA wrapped around histone proteins to form chromatin, chromatin forms chromosomes All is isolated from cytoplasm by the nuclear envelope which is the double membrane After transcription, messenger RNA/ mRNA leaves the nucleus via nuclear pores but DNA/ chromosomes are too long to fit Plasmids are additional loops of DNA, only have a few genes on them and its where you'd find the genes for antibiotic resistance and bacteria either don’t have them or have them in varying numbers

Answer 39

Found on some eukaryotic cells Whip like tail structure Function: for mobility and sometimes as a sensory organelle for chemical stimuli

Answer 40

Hairlike projections out of cells Can either be stationary cilia or mobile cilia Mobile cilia help move substances in a sweeping motion Stationary cilia are important in sensory organs such as the nose

Answer 41

Made up of microtubules Occurs in pairs to form a centrosome Involved in the production of spindle fibre which is essential in organsising the position of chromosomes in mitosis and meiosis (cell division) Consists of two bundles of microtubules at right angles to each other Microtubules are made of tubulin protein subunits and are arranged to form a cylinder Before a cell divides the spindle made of threads of tubulin forms from the centrioles Chromosomes attach to the middle part of the spindle and motor proteins walk along the tubulin threads pulling the chromosomes to opposite ends of the cell Centrioles are involved in formation of cilia and undulipodia Before cilia form, the centrioles multiply and line up beneath the cell surface membrane Microtubules then sprout outwards from each centriole forming a cilium or undulipodium

Answer 42

A network of fibres found within the cytoplasm all over a cell Consists of microfilaments, microtubules and intermediate fibres Provides mechanical strength to cells, helps maintain the shape and stability of a cell and many organelles are bound to the cytoskeleton Microfilaments are responsible for cell movement Microtubules are responsible for creating a scaffold-like structure Intermediate fibres help to provide mechanical strength Microfilaments made of subunits of the protein actin Each microfilament is about 7nm in diameter Intermediate filaments about 10nm in diameter Microtubules about 18-30nm in diameter Cytoskeletal motor proteins, myosins, kinesins and dyneins and molecular motors - are also enzymes and have a site that binds to and allows hydrolysis of ATP as their energy source Protein microfilaments within the cytoplasm fibe support, mechanical strength, keep the cells shape stable and allow cell movemen Microtubules provide shape and support to cells and help substances and organelles to move through the cytoplasm within a cell Form the track along which motor proteins

Answer 43

- Rough and smooth ER both have folded membranes called cisternae - The only difference is that the rough have ribosomes on the cisternae - RER - has the function of protein synthesis for proteins destined to leave the cell, the proteins are transported through the RER and into the secretory vesicles - SER - where lipids and carbohydrates are synthesised and stored

Answer 44

A system of membranes containing fluid-filled cavities (cisternae) that are continuous with the nuclear membrane is the intracellular system - cisternae form channels for transporting substances from one area of a cell to another Provides a large surface area for ribosomes which assemble amino acids into proteins These proteins then actively pass through the membrane into the cisterna and are transported to the golgi apparatus for modification and packaging

Answer 45

A system of membranes containing fluid-filled cavities (cisternae) that are continuous with the nuclear membrane Contains enzymes that catalyse reactions involved with lipid metabolism such as: Synthesis of cholesterol, lipids/phospholipids needed by the cell, steroid hormones Its involved with the absorption, synthesis and transport of lipids from the gut

Answer 46

Secretory vesicles bring material to and from the folgi apparatus Stack of membrane bound flattened sacs Proteins are modified: Adding sugar molecules to make gylcoproteins, lipid molecules to make lipoprotiens, being folded into their 3D shape Proteins are packaged into vesicles that are pinched off and then: stored in the cell, move to plasma membrane either to be incorporated into plasma membrane or exported outside of cell Folded membranes making the cisternae Secretory vesicles that pinch off from the cisternae function : add carbohydrates to proteins to form glycoproteins, produce secretory enzymes, secrete carbohydrates, transport, modify and store lipids, form lysosomes, molecules are ‘labelled’ with their destination Finished products are transported to cell surface membrane in secretory vesicles here they fuse with the membrane and the contents are released

Answer 47

Can be created by golgi apparatus They are vesicles/bags of digestive enzymes - can contain 50 different enzymes Function: hydrolyse phagocytic cells (bacteria), completely break down dead cells (autolysis) Small bags formed from the golgi apparatus and each is surrounded by a single membrane Contain powerful hydrolytic (digestive) enzymes Are abundant in phagocytic cells such as neutrophils and macrophages (types of white blood cells) that can ingest and digest invading pathogens such as bacteria Have two key features Lysosomes contain powerful digestive enzymes such as proteases - these digest large molecules into smaller soluble molecules The internal fluid in a lysosome is acidic - thats because lysosomal enzymes have an optimum pH which is acidic Firstly, lysosomes play a key role in phagosytosis for example in white blood cells Firstly wbcs forms a vacuole around the bacteria - this vacuole is called a phagosome which is the now fused by lysosomes Lysosomal enzymes now digest the bacteria and the soluble digestion products now pass into the cytoplasm Lysosomes can also be used to destroy organelles that are damaged or no longer functional In this case organelle is surrounded by a vacuole and lysosomes fuse with the vacoule membrane and again lysosomal enzymes now digest the organelle Digestion products are absorbed into the cytoplasm and can be reused to make new organelles Sometimes lysosomes transfer their enzymes outside of the cell by exocytosis, eg/ to digest and remove unwanted proteins or dead cells function: lysosomes keep the powerful hydrolytic enzymes separate from the rest of the cell Lysosomes can engulf old cell organelles and foreign matter, digest them and return the digested components to the cell for reuse

Answer 48

These are protrusions from the cell and are surrounded by the cell surface membrane Each contains microtubules Are formed from centrioles The epithelial cells lining your airways each have many hundreds of cilia that beat and move the band of mucus Nearly all cell types in the body have one cillium that acts as antenna - contains receptors and allows cell to detect signals about its immediate environment Only type of human cell to have an undulipodium (a longer cilium) is a spermatozoon- undulipodium enables spermatozoon to move

Answer 49

Lysosomes fusing with phagosomes in phagocytosis which releases the digestive enzymes to hydrolyse/destroy pathogens After whatever the digestive enzymes are breaking down, the lysosomes will then fuse with the cell membrane and that will release its contents to the outside of the cell

Answer 50

2-5 micrometers Surrounded by two membranes with a fluid filled space between them Inner membrane is highly folded into cristae and inner part of mitochondrion is a fluid filled matrix Double membrane bound organelle Inner membrane is folded to form cristae Fluid centre called rhe mitochondrial matrix - site of some of the stages of aerobic respiration Contain their own ribosomes and loops of DNA so they can create the enzymes necessary for respiration inside of the organelle itself function : site of aerobic respiration, site of ATP production, contains DNA to code for the enzymes needed for respiration Found in all eukaryoti organisms Produces ATP In aerobic respiration, the carbohydrate glucose is broken down to carbon dioxide and water The energy contained in the chemical bonds of glucose is transferred to ATP (COME BACK TO THIS) Mitochondria have a double membrane - outer/inner mitochondrial membrane In between these membranes we have the intermembrane space Within mitochondria we have a fluid called the matrix The inner membrane is highly folded - these folds are called cristae By folding the inner membrane, we have a great deal of surface area In mitochondria we also find a loop of mitochondrial DNA The DNA contains the genes for some of the enzymes involved in aerobic respiration Mitochondria also contains mitochondrial ribosomes - these synthesis the proteins encoded by the mitochondrial DNA We tend to find larger numbers of mitochondria in cells which require a lot of energy - the mitochondria in these cells often obtain larger number of cristae which provides increased surface area Function Site of ATP production during anaerobic respiration Self replicating, so more can be made if cells energy needs increase Abundant in cells where much metabolic activity takes place

Answer 51

Ribosomes and cytoskeleton including centrioles are not covered by membranes

Answer 52

Made in the nucleolus as two separate subunits which pass through the nuclear envelope into the cell cytoplasm and then combine Some remain free in the cytoplasm and some attach to the endoplasmic reticulul Made of ribosomal RNA Very very small, spherical organelles about 20nm in diameter made up of two sub units of protein and rRNA 80S - large ribosomes found in the cytoplasm of eukaryotic cells (25nm) 70S - smaller ribosomes found in prokaryotic cells, mitochondria and chloroplasts Function: where protein synthesis occurs Ribosomes bound to exterior of RR are mainly for synthesising proteins that will be exported outside the cell Ribosomes that are free in cytoplasm, either singly or in clusters are primarily the site of assembly of proteins that will be used inside the cell

Answer 53

Formed of cytosol - jelly like substance that is mostly water Contains enzymes, substrates, cofactors/coenzymes and mineral ions involved in biochemical reaction

Answer 54

Are large organelles (4-10 micrometres ) Surrounded by a double membrane Inner membrane is continuous with stacks of flattened membrane stacks called thylakoids which contain chlorophyll Each stack or pile of thylakoids is called a granum (plural: grana) The fluid filled matrix is called the stroma Chloroplasts contain loops of DNA and starch grains Contains thylakoids (folded membranes embedded with pigment) Stacks are called grana for plural or granum for singular Fluid filled stroma contains enzymes for photosynthesis Found in plants Site of photosynthesis

Answer 55

First stage of photosynthesis when light energy is trapped by chlorophyll and used to make ATP occurs in the grana Water is also split to supply hydrogen ions Second stage: when hydrogen reduces carbon dioxide, using energy from ATP to make carbohydrates occurs in the stroma Dont find chloroplasts in parts of the plant that do not photosynthsise eg/ roots The energy that was trapped in photosynthesis is now contained within the chemical bonds in the glucose molecule Photosynthesis actually consists of two dets of reactions The light dependent reactions use chlorophyll to harvest light energy - then energy is then transferred into the chemical bonds of other molecules such as ATP - only take place in the presence of light Light independent reactions - where glucose is formed - do not require light - take place during both light and dark conditions Chloroplasts are surrounded by a double membrane - these membranes control which molecules enter and leav the chloroplast Inside the chloroplast we find membrane bound flattened discs - these discs are called thylakoids - where the light dependent reactions take place Thylakoids contain the chlorophyll and enzymes needed for the light dependent reactions Thylakoids are stacked uo on top of ech other A stak of thyalkoids is called granum and light can be absorbed more efficiently Thylakoids on different grana are connected to eahother by flattened membrsnes called lamellae - play a role in light dependent reactions and allow chemicals ro pass through the grana Chloroplasts contain fluid material called the stroma- where light independent reactions take place Stroma contains the enzymes needed for the light dependent reactions This glucose can be converted to the polysaccharide starch which is stored in the chloroplast as starch granules Chloroplasts also contain a loop of DNA which contains genes which encode some of the proteins needed for protein synthesis Chloroplasts contain ribosomes which synthesis the proteins encoded by the chloroplast DNA

Answer 56

In plant and fungi cells - not in animal cells Plants - made of microfibrils of the cellulose polymer Fungi - made of chitin, a nitrogen-containing polysaccharide Provide structural strength to the cell

Answer 57

Surrounded by a membrane called the tonoplast and contains fluid Only plant cells have a large permanent vacuole Its filled with water and solutes and maintains cell stability because when full it pushes against the cell wall making cell turgid If all plant cells are turgid then it helps to support the plant

Answer 58

Found in all cells Made up of phospholipid bilayer - molecules embed within and attached on the outside (proteins,carbohydrates, cholesterol) Phospholipid bilayer - 2 layers of phospholipids with a hydrophilic heads and hydrophobic tails region In water, this structure naturally forms Limits molecule ion transport based on site of charge - may contain transmembrane protein to be selectively permeable to specific substance Cholesterol affects the fluidity and therefore the permeability of the membrane Controls the entrance and exit of molecules

Answer 59

1) Polypeptide chains are synthesised on the RER (ribosomes on the outside) 2) These polypeptide chains move to the cisternae in the RER and are packaged into vesicles to be sent to the Golgi apparatus for further modification via the cytoskeleton 3) In the golgi apparatus, the proteins are modified and packaged into vesicles 4) The secretory vesicles carry the proteins to the cell surface membrane where it fuses and releases the protein by exocytosis

Answer 60

Prokaryotic cell: the capsule is a slimy layer made of protein on the very outside Function: prevents the bacteria from desiccating (drying out) and it also helps to cover the antigens to make it harder for the host immune system to detect the bacteria - protects the bacteria against the host’s immune system

Answer 61

Contains a material called nucleoplasm Nucleoplasm contains molecules such as nucleotides and enzymes which are needed for DNA nad RNA synthesis Surrounding the nucleus we have a double membrane called the nuclear envelope - consists of two phospholipid bilayers Within nuclear envelope we find nuclear pores - is to allowe molecules to enter or leave the nucleus RNA nucleotides enter the nucleus through nuclear pores from the cytoplasm and these nucleotides are used in the nucleus to synthesise messenger RNA - messenger RNA then leaves the nucleus via nuclear pore and undergoes translation on a ribosome Outer membrane of the nuclear envelope is continuous with the RER RER plays a significant role in protein synthesis Nucleus contains dark material called chromatin - consists of DNA coiled around protein called histones - together DNA and histone proteins form chromosomes Chromosomes are not visible inside the nucleus under the cell is undergoing mitosis or meiosis Inside nucleus theres a region which is darker than the rest - nucleolus - is where a special type of RNA is produced - this is called rRNA - forms part of the structure of ribosomes Nucleolus is also where ribsome subunits are assembled During translation the genetic information in the mRNA is used to synthesise the protein required

Answer 62

Runs through the cytoplasm Three components: microfilaments, microtubules, microfibres Microfilaments have the narrowest diameter and microtubules have the greatest diameter Intermediate fibres have a diameter in between the other two Microfilaments - narrow fibres containing the protein actin, these atin fibres can contract, are involved in cell movement, play a role during cell division Last part of cell division is called cytokinesis During cytokinesis the cell membrane is pulled inwards dividing the cytoplams into two - this process involves the action of microfilaments Intermediate fibres are formed from a number of different proteins and the rold of this is to strengthen the cell Microtubules are framed from subunits of the protein tubulin - tubulin subunits assemble to form tubulin polymers which then form hollow microtubules Microtubules are involved in the movement of organelles, form the spindle fibres which are involved in the movement of chromosomes during meiosis and mitosis By forming a complex network in the cytoplasm, microtubules help to determine the shape of cells

Answer 63

Can find a pair of centrioles in lot of different eukaryotic ells including animal cells Certain relatively simple plants/algae can have centrioles We dont find them in flowering plants or most fungi Centrioles are made up of microtubules Centrioles lie at right angles to eachther and found near the nucleus Together we call pair of centrioles the centrosome Firstly during mitosis and meiosis, centrioles play a role in the assembly of the spindle fibres Spindle fibres are also formed from microtubules How these microtubules are arranged into spindle fibres may be organised by the centrioles Plant cells also form spindle fibres during cell division but flowering plant cells do not contain centrioles so this means centrioles cannot be essential for spindle assembly Centrioles play another role in eukaryotes - in cilia and flagella