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cells Flashcards

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1
Q

Describe the cell surface membrane

A

Found on the surface of animal cells and just inside the cell wall of other cells. Mainly lipids and proteins. Regulates the movement in and out of cells. Also has receptors to allow it to respond to chemicals

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2
Q

Describe the nucleus

A

Large organelle surrounded by a nuclear envelope which contains many pores. Nucleus contains chromosomes (made from linear protein bound DNA), and one or more nucleolus . Controls cells activities by controlling DNA transcription. Pores allow substances to move between nucleus and the cytoplasm. Nucleolus makes ribosomes

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3
Q

Describe mitochondria

A

Double membrane bound. Inner one folded to form cristae. Inside is matrix which contains enzymes involved in respiration. Site aerobic respiration, which produces ATP. Found in large numbers in cells are very active

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4
Q

Describe chloroplasts

A

Double membrane bound. Membranes inside called thylakoids. Stack of thylakoids called grana, which are linked by lamellae. Site of photosynthesis. Some parts happen in grana others in stroma (fluid in chloroplasts).

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5
Q

Describe the Golgi apparatus

A

Group of fluid filled membrane bound flattened sacs. Vesicles are often seen at the edges. Processes and packages new lipids and proteins and also makes lysosomes

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6
Q

Describe the golgi vesicles

A

Small fluid filled sac in cytoplasm, surrounded by a membrane and produced by the Golgi. Stores lipids and proteins made by the Golgi and transports them out of the cell

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7
Q

Describe the lysosomes

A

Round organelle surrounded by membrane. Type of Golgi vesicle which contains digestive enzymes called lysozymes. Can be used to digest invading cells or break down worn out components of the cell

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8
Q

Describe the ribosome

A

Small organelle floating free in cytoplasm and attached to the rER. Made up of proteins and RNA and not membrane bound. Site of protein synthesis

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9
Q

Describe the rough endoplasmic reticulum

A

System of membranes enclosing a fluid filled space. Surface covered with ribosomes. Folds and processes proteins that have been made at ribosomes

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10
Q

Describe the smooth endoplasmic reticulum

A

Similar to rER but no ribosomes. Synthesises and processes lipids

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11
Q

Describe the cell wall

A

Rigid structure that surrounds plant, algal and fungal cells. Plants and algae= cellulose. Fungi= chitin. Supports plants and prevents them changing shape

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12
Q

Define tissue, organ and organ system

A

Tissue: a group of cells working together to carry out a function
Organ: different tissues working together
Organ system: different organs working together

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13
Q

Describe a prokaryotic cell wall

A

Made of murein (a glycoprotein). Supports the cell and prevents it changing shape

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14
Q

Describe the flagellum

A

Long hair like structure that rotates to make cell move

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15
Q

Describe prokaryotic DNA

A

Floats free in cytoplasm. Circular DNA, present as one long coiled up strand. Not attached to any histone proteins

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16
Q

Describe plasmids

A

Small loops of DNA that aren’t part of the main circular DNA molecule. Can be passed between prokaryotes

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17
Q

Describe plasmids

A

Small loops of DNA that aren’t part of the main circular DNA molecule. Can be passed between prokaryotes

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18
Q

Describe the process of binary fission

A
  1. Circular DNA and plasmids replicate. Main DNA loop once but plasmids multiple times
  2. Cell gets bigger and DNA loops move to opposite poles of the cells
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19
Q

What does acellular mean?

A

Not cells or living things

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20
Q

Describe the structure of a virus

A

No cell surface membrane, cytoplasm or ribosomes. Have a protein coat called a capsid, with attachment proteins sticking out. These allow the viruses to cling on to a suitable host cell

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21
Q

Describe the process of viral replications

A
  1. Virus attaches to host cell receptor proteins
  2. Genetic material is released into cell
  3. Genetic material and proteins are replicated by host cell ‘machinery’
  4. Viral components assemble
  5. Replicated viruses released from host cell
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22
Q

What does magnification and resolution mean?

A

Magnification: how many times bigger the image is than the specimen
Resolution: how well a microscope distinguishes between two points that are close together

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23
Q

What are artefacts?

A

Things seen down microscope that aren’t part of specimen (e.g fingerprints, dust etc)

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24
Q

What are optical and electron microscopes?

A

Optical microscope: uses light to form an image. Max resolution of approx 0.2 micrometers. Can see nuclei and potentially mitochondria. max. magnification of x1500

Electron microscope: uses electrons to form image. Higher resolution so gives a more detailed image. Max resolution of 0.0002 micrometers and magnification of x1500000. Produces black and white images

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25
Q

What are transmission electron microscopes and scanning electron microscopes?

A

TEM: uses electromagnets to form a beam of electrons, which is then transmitted through specimen. Denser parts absorb more so look darker on image. Gives high resolution images but can only view very thin specimens and only dead specimens as uses a vacuum.

SEM: scans a beam of electrons across specimen, knocking electrons off specimen which are gathered in a cathode tube to form an image. Shows surface of specimen and could be 3D. Can be used on thicker specimens but lower resolution than TEM. Also can only use dead specimens

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26
Q

How would you prepare a temporary mount?

A

Pipette a small drop of water onto centre of slide. Use tweezers to place thin section of specimen onto water drop. Add drop of stain and add cover slip, being careful to not get air bubbles

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27
Q

How would you carry out cell fractionation?

A

Homogenisation: physically break up cell by either vibrating or blending. Breaks up plasma membrane and releases cells into solution. Solution must be kept ice cold and isotonic, and a buffer must be used
Filtration: cell solution filtered through gauze to separate large cell/tissue debris
Ultracentrifugation: cell fragments poured into tube, which is put into a centrifuge and spun at low speed. Heaviest organelle (nuclei) separate and form the pellet at the bottom. Rest of the organelles remain in solution- supernatant. Supernatant drained and poured into new tube and process repeated at higher speed each time
Order: nuclei, chloroplasts, mitochondria, lysosomes, endoplasmic reticulum, ribosomes

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28
Q

what is the cell cycle?

A

starts when a cel has been produced by cell division and ends with the cell dividing to produce two identical cells. consists of interphase and mitosis. interphase consists of G1, S and G2

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29
Q

describe interphase:

A

cell carries out normal functions but also prepares to divide. Cell’s DNA is unravelled and replicated to double its genetic content. Organelles are also replicated so it has spare ones and its ATP content is increased.

G1- cell grows and new organelles and proteins are made.
S- cell replicates its DNA, ready to divide by mitosis.
G2- cell keeps growing and proteins needed for cell division are made

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30
Q

What do chromosomes look like at the start of mitosis?

A

As mitosis begins, chromosomes are made of two sister chromatids joined by a centromere. Two chromatids because identical copy made during S phase of interphase

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31
Q

Describe the process of mitosis:

A

Prophase: chromosomes condense, getting shorter and fatter. Centrioles start moving to opposite ends of cell, forming network of protein fibres called the spindle. Nuclear envelope breaks down and chromosomes lie free in cytoplasm

Metaphase: chromosomes line up along middle of cell and become attached to the spindle by their centromere

Anaphase: centromeres divide, separating each pair of sister chromatids. Spindles contract, pulling each chromatid to opposite poles of cell, centromeres first. Chromatids appear V-shaped

Telophase: chromatids reach opposite poles on the spindle. Uncoil and become long and thin (now chromosomes again). Nuclear envelope forms around each group of chromosomes so now 2 nuclei. Cytoplasm divides (cytokinesis), and now 2 genetically identical daughter cells.

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32
Q

how do you calculate mitotic index?

A

number of cells with visible chromosomes / total number of cells observed

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33
Q

Define tumour and cancer:

A

Tumour- mass of cells which divide uncontrollably
Cancer- tumour that invades surrounding cells

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34
Q

How do cancer treatments work and affect different stages of the cell cycle?

A

designed to disrupt the cell cycle in order to control the rate of cell division. Treatments are unable to distinguish between normal and tumour cells. However tumour cells divide much more rapidly than normal cells, so more likely to kill tumour cells

G1 (cell growth and protein production)- some chemo prevents the synthesis of enzymes needed for DNA replication. If these aren’t produced, cells are unable to enter S phase, disrupting cell cycle and forcing cell to kill itself

S (DNA replication)- radiation and some drugs damage DNA. At several points in the cell cycle, DNA is checked for damage. If severe damage is detected, the cell will kill itself

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35
Q

what does partially permeable mean?

A

Lets some molecules through but not others

36
Q

Describe the fluid mosaic model of the cell membrane:

A

Phospholipid molecules form a continuous bilayer. Phospholipids are constantly moving (“fluid”). Proteins are scattered through bilayer like tiles in a mosaic,. Includes channel and carrier proteins. Receptor molecules on cell surface membrane allow the cells to detect chemicals from other cells. Some proteins are able to move sideways through the bilayer whilst others are fixed. Some are glycoproteins. Also contains glycolipids and cholesterol

37
Q

what are the role of phospholipids in cell membranes?

A

Form barrier to dissolved substances due to hydrophilic head and hydrophobic tail. Tails face inwards so centre of bilayer is hydrophobic and so doesn’t let water soluble substances (e.g polar and ions) to diffuse. Small non-polar substances and water can diffuse through the membrane.

38
Q

What is the role of cholesterol in the cell membrane?

A

Gives membrane stability. Type of lipid present in all cell membranes (except bacterial). Fits between phospholipids and binds to hydrophobic tail causing them to pack closely together. This restricts the movement of phospholipids, making membranes less fluid and more rigid. Helps maintain the shape of animal cells. Particularly important in cells that aren’t supported by other cells (e.g RBC). Cholesterol also has hydrophobic regions so able to create further barrier to polar substances.

39
Q

How does temperature affect membranes?

A

Affects how much phospholipids in the bilayer can move, affecting membrane structure and permeability.

Below 0°C: phospholipids don’t have much energy so can’t move very much. Packed closer together and the membrane is rigid. Channel and carrier proteins denature, increasing permeability. Ice crystals may form and pierce the membrane, making it highly permeable when it thaws.

0-45°C: phospholipids can move around and aren’t packed as tightly together- membrane is partially permeable. Phospholipids move more because they have more energy so permeability increases

Above 45°C: bilayer starts to melt and membrane becomes more permeable. Water inside cell expands, putting pressure on membrane. Channel and carrier proteins denature so can’t control what enters/leaves so increases permeability

40
Q

Define diffusion and concentration gradient:

A

Diffusion- the net movement of particles from an area of higher concentration to an area of lower concentration.

Concentration gradient- path from an area of higher concentration to an area of lower concentration

41
Q

What factors affect the rate of diffusion?

A

Conc. gradient- the higher it is, the faster the rate. As diffusion occurs, the difference in conc. between the two sides of the membrane decreases until equilibrium is reached so diffusion slows down over time

Thickness of exchange surface- the thinner it is (i.e the shorter the distance particles have to travel) the faster the rate of diffusion

Surface area- the larger the surface area (e.g of the cell surface membrane) the faster the rate of diffusion.

42
Q

What is facilitated diffusion?

A

larger molecules (e.g amino acids) would diffuse extremely slowly through the bilayer because they are so big. Charged molecules (e.g. ions) would diffuse slowly because they’re water soluble and the centre of the bilayer is hydrophobic. To speed things up, large or charged molecules diffuse through carrier or channel proteins

43
Q

How do carrier proteins work?

A

Large molecule attaches to binding site of a carrier protein in membrane
Protein changes shape releasing molecules on opposite side of membrane

44
Q

How do channel proteins work?

A

Form pores in the membrane for charged particles to diffuse through
Different channel proteins for different charged particles

45
Q

What additional factor affects the rate of facilitated diffusion?

A

Number of channel/carrier proteins: once all the proteins in a membrane are in use, facilitated diffusion can’t happen any faster even if you increase the conc. gradient

46
Q

Define osmosis and water potential:

A

Osmosis- diffusion of water molecules across a partially permeable membrane form an area of higher water potential to an area of lower water potential

Water potential- potential of water molecules to diffuse into or out of a solution

47
Q

Why can water diffuse through the membrane but solutes cannot?

A

Water molecules are small and can easily diffuse through the membrane

48
Q

Define isotonic, hypertonic and hypotonic:

A

Isotonic: no difference between cell’s water potential and solution’s water potential
Hypertonic: lower water potential in solution than in cell
Hypotonic: higher water potential in solution than in cell

49
Q

What factors affect the rate of osmosis?

A

Water potential gradient- higher the gradient, faster the rate. As osmosis occurs, the difference in water potential decreases so rate levels out

Thickness of exchange surface- thinner the exchange surface the faster the rate

Surface area of exchange surface- larger area, faster rate

50
Q

What are the two equations for working out serial dilutions

A

C1xV1=C2xV2
V2=V1+volume of distilled water you dilute with

51
Q

Define active transport:

A

Uses energy to move molecules and ions across plasma membranes, usually against a conc. gradient and involving carrier proteins or co-transporters

52
Q

How is ATP involved in active transport?

A

Common energy source in the cell so important for active transport
ATP –> ADP+Pi
This releases energy so solutes can be transported

53
Q

What are co-transporters?

A

Type of carrier protein. Bind 2 molecules at a time. Conc. gradient of one molecule used to move other molecule against its own conc. gradient

54
Q

Describe the co-transport of glucose and Na+ ions:

A
  1. Na+ actively transported out of the epithelial cells in the ileum, into the blood by the sodium potassium pump. This creates a conc. gradient as higher conc. of Na+ in lumen of ileum than in cell
  2. This causes Na+ to diffuse into the epithelial cell from the ileum of the lumen, down their conc. gradient. They do this via the Na+-glucose co-transporter protein. The co-transporter carries glucose into the cell with the Na+ agains glucoses conc. gradient. As a result the glucose conc. in cell increases.
  3. glucose diffuses out of the cell, into the blood, down its conc. gradient through a channel protein by facilitated diffusion
55
Q

What factors affect the rate of active transport?

A

Speed of the individual carrier protein- the faster they work, the faster the rate

No. carrier proteins present- the more carrier proteins there are, the faster the rate

Rate of respiration in cell and availability of ATP- if respiration is inhibited, active transport can’t take place

56
Q

Define antigens and foreign antigens:

A

Antigens- molecules that can generate an immune response when detected by the body

Foreign antigens- antigens that aren’t normally found in the body

57
Q

What are the 4 types of antigens the immune system can identify?

A

Pathogens- organisms that cause disease (e.g. bacteria, viruses and fungi) all have antigens on their surface. These are identified by the immune system cells, which then respond to destroy the pathogens

Abnormal body cells- cancerous or pathogen infected cells have abnormal antigens on their surface, which trigger immune cells

Toxins- these are poisonous molecules (not cells). Some toxins are produced by bacteria. The immune system can respond to toxins as well as pathogens that release them

Cells from other individuals of the same species- when you receive cells from another person (e.g organ transplants or blood transfusion) those cells will have some antigens that are different to your own. The foreign antigens trigger an immune response. This response leads to the rejection of transplanted organ if drugs aren’t taken to suppress the recipients immune system.

58
Q

How can blood transfusions generate an immune response?

A

The most important antigens are ABO blood group antigens. If the donated blood contains donated A or B antigens that aren’t recognised by the immune system, they will generate an immune response.

59
Q

What are the three different types of immune cells?

A

Phagocyte- type of WBC that carries out phagocytosis. Found in the blood and in tissues, and are the first cells to respond to trigger an immune response

T-Cell- type of WBC which has receptors on its surface that bind to complementary antigens presented to it by phagocyte

B-Cell- type of WBC that are covered in antibodies

60
Q

Describe phagocytosis:

A

Phagocyte recognises the foreign antigens on a pathogen. Cytoplasm of phagocyte moves around pathogen and engulfs it in a phagosome. Lysosome fuses with phagosome, and lysozymes break down the pathogen. Phagocyte then presents the antigens on its cell-surface membrane, acting as an antigen presenting cell

61
Q

Describe the role of T-Cells in the immune response:

A

Different types of T-cells respond in different ways. Helper T-Cells release chemical signals that activate and stimulate phagocytosis and cytotoxic T-Cells, which kill abnormal and foreign cells. Helper T-Cells also activate B-Cells which secrete antibodies

62
Q

Describe the role of B-Cells in the immune response:

A

Each B-Cell has a different shaped antibody on its membrane, so different ones bind to different antigens. When the antibody on the surface of a B-Cell meets a complimentary shaped antigen it binds to it (antigen-antibody complex). This, together with substances released by the helper T-Cells activates the B-Cell. This process is called clonal selection. The activated B-Cell divides into plasma cells

63
Q

How are antibodies produced by the immune response?

A

Plasma cells are identical to the B-Cells. They secrete lots of antibodies specific to the antigen. These are called monoclonal antibodies. They bind to the antigens on the surface of the pathogen to form lots of antigen-antibody complexes.

64
Q

What is agglutination?

A

Antibody has two binding sites and so can bind to two antigens at the same time, clumping pathogens together. Phagocytes can phagocytose many pathogens at once

65
Q

Describe the structure of an antibody:

A

Y shaped protein, made of light chain and heavy chain. Specificity depends on its variable regions, which form the antigen binding site. Each antibody has a variable region with a unique tertiary structure thats complementary to one specific antigen. All antibodies have the same constant region

66
Q

What part of the immune system is involved in the cellular and humoral response?

A

Cellular- T-Cells and otger immune cells that they interact with

Humoral- B-cells, clonal selection and the production of antibodies

67
Q

Describe the primary response:

A

When an antigen enters the body for the first time, it activates the immune system. Primary response is slow because they’re aren’t many B-Cells that can make the antibody needed to bind to it. Eventually, body produces enough of the antibody to overcome the infection, meanwhile the infected person will show symptoms. After exposure, T and B-cells produce memory cells, which remain in the body for a long time. Memory T-Cells remember the specific antigen, whilst memory B-Cells record the specific antibodies needed to bind the antigen. Person is now immune- immune system has ability to respond quickly to the specific infection

68
Q

What is the secondary response?

A

If the same pathogen enters the body again, the immune system will produce a quicker and stronger immune response. Clonal selection happens faster. Memory B-Cells are activated and rapidly divide into plasma cells to produce the right antibody to the antigen. Memory T-Cells are activated and divided into the correct type of T-Cell to kill the cell carrying the antigen. The secondary immune response often gets rid of the pathogen before any symptoms appear

69
Q

What is active immunity and what are the two types?

A

Immune system makes its own antibodies after being stimulated by an antigen

Natural- catch a disease
Artificial- vaccination

70
Q

What is passive immunity an what are the two types?

A

Given antibodies made by a different organism

Natural- baby receives antibodies from mum
Artificial- injected with antibodies from someone else

71
Q

What is the difference between active and passive immunity?

A

Active requires exposure to the pathogen whilst passive doesn’t.
Active takes a while for protection to develop, whilst passive offers immediate protection
Active produces memory cells, passive does not
Active offers long term protection, passive offers short term

72
Q

Describe vaccination:

A

Contain antigens that cause your body to produce memory cells against a pathogen without the pathogen causing disease- become immune without any symptoms. Vaccines protect the individuals that have them and also give herd immunity because reduces the occurrence of the disease. Vaccines always contain antigens. They can be injected or taken orally. Disadvantage of oral is they can be broken down by enzymes in the gut, or molecules may be too big to absorb into blood. Sometimes booster vaccines given to make sure more memory cells are produced.

73
Q

What are the ethical issues of vaccines?

A

All vaccines are tested on animals first and animal based substances also may be used to produce a vaccine which some people disagree with.
Testing vaccines on volunteers can be risky, as they may put themselves at unnecessary risk of contracting a disease if they think they’re protected.
Some people don’t want vaccines due to the risk of side effects but are still protected due to herd immunity which some people think is unfair
If there was an epidemic, there would be a rush to receive a vaccine and difficult decisions have to be made about who would be first to receive it

74
Q

Define antigenic variation:

A

different antigens formed due to changes in the genes of a pathogen

75
Q

How do targeted anti-cancer drugs use monoclonal antibodies?

A

Cancer cells have antigens called tumour markers that aren’t found on normal body cells. Monoclonal antibodies can be made that will bind to the tumour markers. You can also attach monoclonal antibodies to anti-cancer drugs. When the antibodies come into contact with the cancer cells, they will bind to the tumour markers, so the drug only accumulates in the body where there are cancer cells so fewer side effects

76
Q

How do pregnancy tests use monoclonal antibodies?

A

Application area contains antibodies that are complementary to the hCG protein, bound to a coloured bead. When urine is applied, the hCG binds to antibody, forming antigen-antibody complex. The urine moves up test strip, carrying any beads with it. The test strip contains immobilised hCG antibodies. If there is hCG present, the strip turns blue because the immobilised antibody binds to any hCG which is already bound to the blue bead. If no hCG present, the beads will pass through the test area without binding to anything.

77
Q

What is the ELISA test?

A

Enzyme linked immunosorbent assay.
Allows you to see if patient has any antibodies to a certain antigen (or vice versa)

78
Q

Describe the direct and indirect ELISA test:

A

Direct- uses a single antibody. Antigens from a patient sample are bound to the inside of a well in a well plate. A detection antibody which is complementary to the antigen of interest is added. The antibody has an enzyme attached. If the antigen of interest is present in patient sample, the detection antibody will bind to it. Well is then washed to remove any unbound antibody and a substrate solution is added. If the detection antibody is present, enzyme reacts with the substrate to give a colour change.

Indirect- HIV antigen is bound to bottom of well. Sample of pt’s blood plasma is added to the well. If there are any HIV specific antibodies in the plasma, they will bind to the HIV antigen. Well is then washed out to remove any unbound antibody. Secondary antibody with enzyme attached is added. Secondary antibody will bind to first antibody. Washed again. Substrate solution added. If colour change then person is infected with HIV

79
Q

What effect does HIV have on host cells?

A

HIV infects and eventually kills helper T-cells, which act as the host cells. Without enough helper T-cells, the immune system is unable to mount an effective immune response to infections because other immune system cells don’t behave how they should. People with HIV develop AIDS when their helper T-cell numbers reach a critically low level

80
Q

What are the symptoms of AIDS:

A

Initial symptoms include minor infections of mucus membranes and recurring respiratory infections. As AIDS develops, the number of immune system cells decreases further and people become susceptible to more serious infections (e.g chronic diarrhoea or TB) During the late stages, patients have very low levels of immune cells and develop a range of severe infections which kill the patient.

81
Q

Describe the structure of HIV:

A

Spherical structure. Made up of genetic material (RNA) and reverse transcriptase. Capsid and extra outer layer (envelope) made from membrane stolen from cell membrane of host cell. Attachment proteins stick out of envelope

82
Q

How does HIV replicate?

A
  1. Attachment protein attaches to receptor molecule on host cell’s cell membrane.
  2. Capsid released into cell where it uncoats and releases the genetic material into cell’s cytoplasm
  3. Inside the cell, reverse transcriptase is used to make a complementary strand of DNA from the viral RNA template
  4. From this, double stranded DNA is made and inserted into the human DNA
  5. Host cell enzymes are used to make viral proteins from the viral DNA found within the human DNA
  6. Viral proteins are assembled into new viruses, which bud from the cell and go on to infect new cells
83
Q

How do antibiotics affect bacteria?

A

Kill bacteria by interacting with their metabolic reactions. Target the bacterial enzymes and ribosomes used in these reactions. Bacterial enzymes and ribosomes are different to human ones so antibiotics are designed to only target bacterial ones

84
Q

Why can’t antibiotics kill viruses?

A

Viruses don’t have their own enzymes and ribosomes, they use the host cells so antibiotics can’t target them. Most antiviral drugs are designed to target the few virus specific-enzymes

85
Q

How can we control HIV infections?

A

No cure or vaccine but antiviral drugs can be used to slow down the progression. Best way to control HIV is to control its spread. Spread via unprotected sex, infected bodily fluids and through a HIV positive mother to fetus.

biology year 12 (4 decks)

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