Cells Flashcards

Question

Function of Golgi vesicles Golgi vesicles ... ___ are a special type of Golgi vesicle. They contain enzymes called ___ Lysozymes aid the ...

Answer 1

Function of Golgi vesicles Golgi vesicles store and transport modified proteins and lipids from the Golgi apparatus to target cells. Lysosomes are a special type of Golgi vesicle. They contain enzymes called lysozymes. Lysozymes aid the breakdown of proteins, polysaccharides, lipids, nucleic acids and old organelles.

Answer 2

Ribosomes and the Endoplasmic Reticulum Proteins are made in ribosomes. Proteins may then be folded and processed by the rough endoplasmic reticulum (RER). The smooth endoplasmic reticulum makes and processes lipids.

Answer 3

Structure of ribosomes Ribosomes can be free floating in the cytoplasm or attached to the cytoplasmic side of the endoplasmic reticulum (ER). Ribosomes are very small organelles made of protein subunits. This means that ribosomes are not covered by a membrane.

Answer 4

Function of ribosomes Ribosomes are in charge of protein synthesis. Protein synthesis is an essential function of all cells. This is why ribosomes are found in practically every cell.

Answer 5

Structure of the ER The ER is a series of interconnected membranous sacs and tubules. The membrane of the ER is a phospholipid bilayer embedded with proteins. The smooth ER (SER) membrane has no ribosomes but the rough ER (RER) membrane has many ribosomes on its surface.

Answer 6

Function of the RER and SER The RER is responsible for processing and folding proteins. The SER is responsible for making and processing lipids.

Answer 7

Cell Wall and Cell Vacuole The cell wall is a structure external to the plasma membrane. Cell vacuoles are found in plant cell cytoplasm.

Answer 8

Structure of cell walls The cell wall is a rigid covering that protects the cell. Plant, fungal and algal cells all have cell walls. The major organic molecule in fungal cell walls is chitin. Plant and algal cell walls are made of cellulose. Cellulose is a polysaccharide made up of glucose units.

Answer 9

Function of cell walls The cell wall provides structural support and gives shape to the cell.

Answer 10

Structure of cell vacuoles Plant cells each have a large central vacuole that occupies most of the area of the cell. These vacuoles are surrounded by a membrane called the tonoplast and contain a weak solution of salts and sugars called cell sap. Cell vacuoles are found in the cytoplasm of plant cells but are NOT present in animal cells.

Answer 11

Function of cell vacuoles The central vacuole allows the cell to remain rigid. When the central vacuole holds more water, the vacuole pushes against the cell wall and pressure is maintained. This stops the plant from wilting. The vacuole also isolates certain chemicals that are unwanted by the rest of the cell.

Answer 12

Prokaryotic Cells Prokaryotic cells have some features that are also found in eukaryotic cells. Prokaryotic cells may also contain plasmids, a capsule and one or more flagella.

Answer 13

Prokaryotes vs eukaryotes Features common to these types of cells are: A plasma membrane. Cytoplasm. DNA. Ribosomes (ribosomes are smaller in prokaryotes). So, the main difference in terms of organelles is that prokaryotes do NOT have any membrane-bound organelles (e.g. nucleus, mitochondria, Golgi apparatus etc.).

Answer 14

DNA in prokaryotes Prokaryotic DNA is found as a circular molecule in the cytoplasm. Some prokaryotes have smaller loops of DNA called plasmids that are not part of the main circular DNA molecule. Bacteria can exchange plasmids with other bacteria, sometimes receiving beneficial new genes that the recipient can add to their chromosomal DNA. Antibiotic resistance is one trait that often spreads through a bacterial colony through plasmid exchange.

Answer 15

Capsule The capsule enables prokaryotic cells to attach to surfaces in its environment.

Answer 16

Flagella, pili and fimbriae Some prokaryotes have flagella, pili, or fimbriae: Flagella are tail-like and used for locomotion. Some prokaryotes have none and others have more than one. Pili are used to exchange genetic material during a type of reproduction called conjugation. Fimbriae are used by bacteria to attach to a host cell.

Answer 17

Binary Fission Prokaryotes, such as bacteria, replicate by binary fission. For unicellular organisms, cell division is the only method to produce new individuals.

Answer 18

Binary fission 1) Replication of genetic material Binary fission in prokaryotic cells involves replication of the circular DNA and of plasmids. 2) Migration of genetic material The two sets of genetic material migrate towards opposite poles. 3) Cytoplasm begins to divide The cytoplasmic contents must be divided to give both new cells the machinery to sustain life. 4) Formation of daughter cells Two daughter cells are formed, each with a single copy of the circular DNA and a variable number of plasmid copies. Daughter cells are genetically identical to the parent cells and identical to each other. The only difference between the daughter cells is the number of plasmid copies in each cell.

Answer 19

Viruses Viruses are acellular and non-living. Virus particles include genetic material, a capsid and attachment proteins.

Answer 20

Structure Viruses are made up of nucleic acids. The nucleic acids are surrounded by a protein called a capsid. Viruses are smaller than bacteria.

Answer 21

Living cells Viruses are NOT considered living because: They have no nucleus, plasma membrane, cytoplasm or ribosomes. They are not made of cells. They cannot reproduce independently.

Answer 22

Function To replicate, viruses have to invade and hijack the reproductive mechanism of a living cell. These cells are then termed host cells. Viruses have attachment glycoproteins that bind to complementary receptors on host cells. They then inject DNA or RNA into the host cell. The host cell divides as normal and the virus is replicated.

Answer 23

Magnification and Resolution Two parameters that are important in microscopy are magnification and resolution

Answer 24

Magnification Magnification is the process of enlarging an object in appearance. The image size is how big the object appears to be in a picture or drawing, which will be in milimeters (mm). The actual size is often given in micrometers (µm) - units must be converted so that they are the same.

Answer 25

Calculating magnification The equation for magnification is: Magnification = size of image ÷ size of real object E.g. A mitochondrion is 20 µm long. An image of the mitochondrion is measured as 20 mm long. What is the magnification? Magnification = 20,000 µm ÷ 20 µm = 1,000x

Answer 26

Resolution Resolution is the ability of a microscope to distinguish two adjacent structures as separate. The higher the resolution, the better the clarity and detail of the image.

Answer 27

Cell Fractionation Cell fractionation separates organelles according to size to allow them to be studied in an electron microscope. The steps involved are: 1) Homogenisation The tissue sample is homogenised using a blender to break the cells. The tissue sample must be kept in specific conditions: Ice cold (reduces enzyme activity that might damage organelles). Isotonic solution (prevents osmosis that could shrink or burst organelles). No osmosis takes place in isotonic solution. ``` Buffered solution (keeps pH constant and avoids damaging the protein structures). ``` 2) Filtration The tissue sample is filtered into tubes through a gauze. The gauze separates larger components from the small, organelles. The organelles are filtered into tubes to be fractionated using ultracentrifugation. 3) Ultracentrifugation The samples are spun at a low speed in a centrifuge. Each tube must be balanced with another tube directly opposite for the centrifuge to work properly. Centrifugation separates the sample into fractions. Heavier organelles are forced to the bottom of the tube. Lighter organelles move towards the top. Cell debris (e.g. cell walls) forms a pellet at the bottom of the tube, leaving the supernatant (a liquid) above it that contains the organelles. 4) Ultracentrifugation The supernatant is poured off and centrifuged at a higher speed to separate the next heaviest organelles (the nuclei). This is repeated at increasingly higher speeds to separate each fraction. 5) Order of fractionation The process of repeated ultracentrifugation produces fractions of cell organelles from heaviest to lightest. ``` This order is: Nucleus. Chloroplasts. Mitochondria. Lysosomes. Endoplasmic reticulum. Ribosomes. ```

Answer 28

What are the steps involved in cell fractionation? 1 The tissue sample is homogenised using a blender to break the cells. 2 The tissue sample is filtered into tubes through a gauze to separate larger components from the small organelles. 3 The organelles are filtered into tubes to be fractionated using ultracentrifugation. 4 The samples are spun at a low speed in a centrifuge to separate the sample into fractions. 5 The supernatant is poured off and centrifuged at a higher speed to separate the next heaviest organelles. This is repeated at increasingly higher speeds to separate each fraction.

Answer 29

Optical (light) microscopes Visible light passes and is bent through the lens system to enable the user to see the specimen. The specimen can be alive. Individual cells are generally transparent and their components are not distinguishable unless they are coloured with special stains. Staining usually kills the cells.

Answer 30

Uses of light microscopes Most student microscopes are classified as light microscopes. Maximum resolution is 0.2 micrometres. The nucleus and mitochondria can be seen with a light microscope. The maximum magnification is around x1,500.

Answer 31

Electron microscopes In contrast to light microscopes, electron microscopes use a beam of electrons instead of a beam of light. This allows higher magnification and higher resolving power. This means that more detail can be seen.

Answer 32

Uses of electron microscopes Electron microscopes have a maximum resolution of 0.0002 micrometres. This is around 1000 times more than light microscopes. The maximum magnification is around x1,500,000.

Answer 33

Types of Electron Microscopes There are two main types of electron microscopes: transmission (TEM) and scanning (SEM) electron microscopes.

Answer 34

TEM In a TEM, the electron beam penetrates the cell and provides details of a cell’s internal structures. TEMs use electromagnets to focus the electron beam. TEMs are high resolution microscopes. In thin specimens, you can see the internal structures of organelles such as chloroplasts.

Answer 35

SEM In a SEM, a beam of electrons moves back and forth across a cell’s surface, creating details of cell surface characteristics. SEMs knock electrons off the specimen and these electrons come together to form an image. SEM images can be three-dimensional. Specimens do NOT have to be thin like when using a TEM. Resolution is lower than that produced by a TEM.

Answer 36

What is the name of the fluid-filled membrane sacs found within the chloroplasts? Thylakoids

Answer 37

Cell Division Viruses require a host cell to divide. Cells that have the ability to divide have a cell cycle.

Answer 38

Phases of the cell cycle The cell cycle has two major phases: interphase and the mitotic phase. During interphase, the cell grows and DNA is replicated. During the mitotic phase, the replicated DNA and cytoplasmic contents are separated, and the cell divides.

Answer 39

Interphase Interphase is subdivided into three growth stages called G1, S and G2 stage. In G1, the cell grows. In S, DNA synthesis happens. In G2, the cell grows some more before the mitotic phases begins.

Answer 40

The mitotic phase Mitosis is the part of the cell cycle in which a eukaryotic cell divides to produce two daughter cells, each with the identical copies of DNA produced by the parent cell during DNA replication. Multicellular organisms go through mitosis to grow and repair damaged tissues.

Answer 41

Stages of Mitosis In mitosis, chromosomes go through interphase, prophase, metaphase, anaphase and telophase.

Answer 42

Stages of mitosis Interphase The cell prepares to divide. DNA is replicated by semi-conservative replication. There are now two copies of every chromosome. The organelles are also replicated. More ATP is produced to be used in cell division.

Answer 43

Stages of mitosis Prophase The nuclear envelope breaks down and the nucleolus disappears. Chromosomes are left floating in the cytoplasm. The chromosomes coil more tightly and become shorter and fatter. They can be seen under a light microscope. Small protein bundles called centrioles move to opposite poles of the cell. Microtubules form the mitotic spindle between the centrioles.

Answer 44

Stages of mitosis Metaphase The chromosomes line up along the mid-line of the cell. In Metaphase, the chromosomes are Maximally condensed. They are attached to the spindle by the centromere.

Answer 45

Stages of mitosis Anaphase The chromosomes break into two chromatids. The sister chromatids separate at the centromere. The spindles contract and pull the chromatids to each pole of the cell.

Answer 46

Stages of mitosis Telophase The chromatids reach the opposite poles and begin to decondense (unravel), becoming chromosomes again. Nuclear envelopes form around the chromosomes so there are now two nuclei. The cytoplasm splits and two daughter cells are formed. The daughter cells are identical to the original cell and to each other. The cell cycle starts again.

Answer 47

Way to remember the stages: ``` I (interphase). Picked (prophase). My (metaphase). Apples (anaphase). Today (telophase). ```

Answer 48

Centromere The central region of a chromosome to which the microtubules of the spindle attach.

Answer 49

Chromatids The two thread-like strands into which a chromosome divides longitudinally during cell division. Each contains a double helix of DNA.

Answer 50

Centriole A pair of small cylindrical organelles located near the nucleus involved in the development of spindle fibres in cell division.

Answer 51

1) Sample preparation Wear gloves and use forceps to handle the tips. Root tips must be sprouting (actively growing). Place into 5 M hydrochloric acid. After 5 minutes, rinse the tips in cold water in a watch glass.

Answer 52

2) Cut the root tips Using a sharp scalpel, cut root tips that are 2 mm long. Place a root tip onto a microscope slide. Ensure the slide is clean to reduce the chances of artefacts.

Answer 53

3) Staining Carefully add 2-3 drops of stain and leave for two minutes. Use a mounted needle to spread out the root tips into a thin layer. Place a coverslip over the top of the tips.

Answer 54

4) Squashing Squash down by applying force to the cover slip. This could be with the flat end of a pencil, or the slide could be covered with a paper towel and pressed. Force must be vertical or the cover slip may break and cause injury.

Answer 55

5) Viewing the sample Place the slide on the microscope stage using the lowest power lens. Focus the lens on the sample using first the coarse control and then the fine control. Move the slide to see the range of cells. The cells closer to the tip will be those more actively dividing. On a lens power of 400x, it should be possible to clearly see the chromosomes in the dividing cells.

Answer 56

The equation for mitotic index for a particular field of view is: Mitotic index = number of cells in mitosis ÷ total number of cells

Answer 57

In a field of view, 29 cells are counted in total. 22 of the 29 cells have visible chromosomes and are actively dividing. 22 ÷ 29 = 0.7586 About 76% of the cells in the sample are undergoing mitosis.

Answer 58

What is used to work out the proportion of cells in the sample that are in mitosis? MITOTIC INDEX

Answer 59

The darker the solution of beetroot, the more pigment has been released because the membrane is more permeable. A darker solution will have a higher reading for absorbance.

Answer 60

Steps Involved in Investigating Cell Membrane Permeability collect beetroot samples put them in ethanol solutions remove the discs and put them in distilled water in a cuvette calibrate the colorimeter measure the absorbance of each solution

Answer 61

Structures of the cell membrane: Plasma membrane The structure that defines the borders of cells and most organelles. Phospholipid The molecules that form a bilayer in membranes. The molecules are made from glycerol, two fatty acids and phosphate-linked head group. Cholesterol Lipid that sits in the core of the membrane.

Answer 62

What absorbance is the colorimeter calibrated to? 520 nm

Answer 63

1) Collect beetroot samples Use a cork borer to collect samples of uniform diameter. Cut discs of a uniform depth using a sharp scalpel on a white tile and rinse in cold water. This removes excess pigment that has leaked through physically broken cell membranes.

Answer 64

2) Add ethanol Prepare at least five concentrations of ethanol (e.g. 0%, 10%, 20%, 30%, 40%) in beakers. Place the discs into the corresponding solution for 10 minutes. Make sure the samples are completely covered by the ethanol solutions and mixed frequently throughout the 10 minutes.

Answer 65

3) Remove the discs Remove the discs from the solutions to prevent further changes and allow a fair comparison between the experiments.

Answer 66

4) Calibrate the colorimeter Calibrate a colorimeter by using a cuvette of distilled water at an absorbance of 520nm. The cuvettes must be dry and the clear sides must not be touched to prevent potential errors in the readings.

Answer 67

5) Measure absorbance Measure the absorbance of each solution. Plot the results in a graph with concentration on the x-axis and absorbance on the y-axis. The darker the solution, the more pigment has been released. This is reflected in a higher reading for absorbance.

Answer 68

Diffusion Diffusion describes the passive movement of particles in fluids (liquids and gases).

Answer 69

Diffusion Molecules move randomly but tend to move into any space available until it is evenly distributed. So, the net movement of particles will be towards the area of lower concentration or down a concentration gradient. Substances such as CO2, O2 and urea can move in and out of cells across cell membranes via diffusion.

Answer 70

E.g. Perfume When you spray perfume, the smell diffuses across the room from the area of high concentration (where you just sprayed it) to the area of low concentration (the other side of the room).

Answer 71

What do we call the net movement of particles from an area of high concentration to an area of lower concentration? diffusion

Answer 72

Large or polar molecules Some materials are too large to move through the membrane. Other materials are polar molecules that are repelled by the hydrophobic part of the membrane. These materials move across the membrane by facilitated diffusion.

Answer 73

Steps Involved in Staining Plant Root Tips prepare the sample cut the root tips stain the root tips squash the root tips view the sample at 400x power w a light microscope

Answer 74

How must force be applied when squashing plant root tips? vertically

Answer 75

Errors in DNA replication can lead to the development of tumours. Drugs can be targeted to damage DNA and kill the cells to prevent spread of a tumour.

Answer 76

The cell cycle is tightly controlled by genes, however errors do happen. If changes to the DNA nucleotide sequence happen within a coding portion of a gene and are not corrected, a gene mutation results.

Answer 77

What phase in interphase produces new organelles and causes the cells to grow in size? g1

Answer 78

What is the normal thickness of the phospholipid bilayer? 5-10nm

Answer 79

The more easily the phospholipid bilayer is dissolved, the more permeable the membrane.

Answer 80

the permeability of cell membranes: pH solvent concentration temperature

Cells Flashcards

(104 cards)