3.2 Cells Flashcards
(107 cards)
1
Q
Cell membrane structure
A
Phospholipid bilayer with embedded intrinsic & extrinsic proteins
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2
Q
Cell membrane function
A
- Selectively permeable barrier
- controls passage of substances in and out the cell
- barrier between internal and external cell environments
3
Q
Nucleus structure
A
- Nuclear pores, nucleolus, DNA and nuclear envelope
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4
Q
Nucleus function
A
- Site of transcription & pre-mRNA splicing – mRNA production
- site of DNA replication
- nucleolus makes ribosomes
- nuclear pore allows movement of substances to/from cytoplasm
5
Q
Mitochondria structure
A
- Double membrane with inner membrane folded into cristae
- 70S ribosomes in matrix
- small, circular DNA
- enzymes in matrix
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6
Q
Mitochondria function
A
- Site of aerobic respiration
- produces ATP
7
Q
Chloroplast structure
A
- Thylakoid membranes stacked to form grana, linked by lamellae
- stroma contains enzymes
- contains starch granules, small circular DNA and 70S ribosomes
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8
Q
Chloroplast function
A
- Chlorophyll absorbs light for photosynthesis to produce organic molecules (glucose)
9
Q
Organisms containing
chloroplasts
A
- Plants
- Algae
10
Q
Golgi apparatus stucture
A
- Fluid-filled, membrane-bound sacs (horseshoe shaped)
- vesicles at edge
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11
Q
Golgi apparatus function
A
- Modifies proteins received from RER
- packages them into vesicles to transport to cell membrane for exocytosis
- makes lysosomes
12
Q
Lysosome structure
A
- Type of Golgi vesicle containing digestive enzymes
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13
Q
Lysosome function
A
- Contains digestive enzymes
- e.g. lysozymes to hydrolyse pathogens/cell waste products
14
Q
Rough endoplasmic reticulum function
A
- Site of protein synthesis
- folds polypeptides to secondary & tertiary structures
- packaging into vesicles to transport to Golgi
15
Q
Smooth endoplasmic reticulum function
A
- Synthesises and processes lipids
16
Q
Cell wall function
A
- Provides structural strength, rigidity and support to cell
- helps resist osmotic pressures
17
Q
Ribosome structure
A
- Small and large subunit
- made of protein and rRNA
- free floating in cytoplasm & bound to RER
- 70S in prokaryotes, mitochondria and chloroplasts
- 80S in eukaryotes
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18
Q
Ribosome function
A
- Site of translation in protein synthesis
19
Q
Rough endoplasmic reticulum structure
A
- System of membranes with bound ribosomes
- continuous with nucleus
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20
Q
Smooth endoplasmic reticulum structure
A
- System of membranes with no bound ribosomes
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21
Q
Cell wall structure
A
- In plant, fungal and bacterial cells
- plants – made of microfibrils of cellulose
- fungi – made of chitin
- bacteria – murein
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22
Q
Cell vacuole structure
A
- Fluid-filled
- surrounded by a single membrane called a tonoplast
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23
Q
Contrast prokaryotic & eukaryotic cells
A
- Prokaryotic cells are smaller
- prokaryotes have no membrane bound organelles
- prokaryotes have smaller 70S ribosomes
- prokaryotes have no nucleus – circular DNA not associated with histones
- prokaryotic cell wall made of murein instead of cellulose/chitin
24
Q
Occasional features of prokaryotes
A
- Plasmids – loops of DNA
- capsule surrounding cell wall – helps agglutination + adds protection
- flagella for movement
25
Cell vacuole function
* Makes cells **turgid** – structural support
* temporary **store** of sugars, amino acids
* coloured pigments attract pollinators
26
Protein carriers
* **Bind** with a molecule, e.g. glucose, which causes a **change in the shape** of the protein
* this change in shape enables the molecule to be **released** to the other side of the membrane
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27
Protein channels
* **Tubes** filled with water enabling **water-soluble ions** to pass through the membrane
* **selective**
* channel proteins only open in the presence of certain ions when they bind to the protein
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28
Features of viruses
* **Non-living** and **acellular**
* contain genetic material, capsid and attachment proteins
* some (HIV) contain a lipid envelope + enzymes (reverse transcriptase)
29
3 types of microscopes
* **Optical** (light) microscopes
* **Scanning electron** microscopes (SEM)
* **Transmission electron** microscopes (TEM)
30
Magnification
* How many times larger the image is compared to the object
* calculated by equation:
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31
Resolution
* The **minimum distance** between two objects in which they can still be viewed as **separate**
* determined by **wavelength** of light (for optical microscopes) or electrons (for electron microcopes)
32
Optical microscopes
* Beam of **light** used to create image
* **glass lens** used for focusing
* **2D coloured** image produced
33
Evaluate optical microscopes
* **Poorer resolution** as long wavelength of light – small organelles not visible
* **lower magnification**
* can view **living** samples
* **simple staining** method
* vaccum not required
34
Transmission electron microscopes
* Beam of **electrons** passes **through the** sample used to create an image
* focused using **electromagnets**
* **2D, black & white** image produced
* can see **internal ultrastructure** of cell
* structures **absorb electrons** and appear **dark**
35
Evaluation TEMs
* **Highest resolving power**
* **high magnification**
* extremely **thin** specimens required
* **complex staining** method
* specimen must be **dead**
* **vaccum** required
36
Scanning electron microscopes
* Beam of **electrons** pass **across** sample used to create image
* focused using **electromagnets**
* **3D, black and white** image produced
* electrons **scattered** across specimen producing image
37
Evaluation SEMs
* **High resolving power**
* **high magnification**
* **thick** specimens usable
* **complex staining** method
* specimen must be **dead**
* **vaccum** required
38
Why calibrate eyepiece graticule?
* Calibration of the eyepiece is required each time the objective lens is changed
* calibrate to work out the **distance between each division** at that magnification
39
Purpose of cell fractionation
* **Break open cells** & remove cell debris
* so organelles can be studied
40
Homogenisation
* Process by which **cells are broken** open so organelles are free to be separated
* done using **homogeniser** (blender)
41
Homogenisation conditions
* **Cold** reduces enzyme activity preventing organelle digestion
* **Isotonic** prevents movement of water by osmosis – no bursting/shrivelling of organelles
* **Buffered** resists pH changes preventing organelle + enzyme damage
42
Ultra-centrifugation
* Homogenate solution **filtered** to remove cell debris
* solution placed in a **centrifuge** which **spins** at a low speed initially
* then increasingly faster speeds to separate organelles according to their **density**
43
Differential centrifugation
* Supernatant first out (spun at lowest speed) is **most dense = nuclei**
* spun at higher speeds
* chloroplasts → mitochondria → lysosomes → RER/SER → ribosomes (least dense)
44
Binary Fission
* Involves **circular DNA** & **plasmids replicating**
* **cytokinesis** creates two daughter nuclei
* each daughter cell has one copy of circular DNA and a variable number of plasmids
45
Cell cycle
1. Interphase (G1, S, G2)
2. nuclear division – mitosis or meiosis
3. cytokinesis
46
Interphase
* **Longest** stage in the cell cycle
* when DNA replicates (S-phase) and organelles duplicate while cell grows (G1 & G2-phase)
* DNA replicates and appears as **two sister chromatids** held by **centromere**
47
Mitosis
* One round of cell division
* **two diploid, genetically identical daughter cells**
* growth and repair (e.g. clonal expansion)
* comprised of prophase, metaphase, anaphase and telophase
48
Prophase
* Chromosomes **condense** and become **visible**
* nuclear envelope **disintegrates**
* in animals – centrioles separate & **spindle fibre structure forms**
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Metaphase
* Chromosomes align along **equator** of cell
* **spindle fibres** released from poles now **attach to centromere** and **chromatid**
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50
Anaphase
* Spindle fibre **contracts** (using ATP) to **pull chromatids**, centromere first, towards **opposite poles** of cell
* centromere divides in two
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51
Telophase
* Chromosomes at each pole become **longer** and **thinner** again
* spindle fibres disintegrate + **nucleus reforms**
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52
Mitotic index
* Used to determine **proportion** of cells undergoing mitosis
* Calculated as a percentage OR decimal
* x100 for percentage
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53
Fluid mosaic model
* Describes the **lateral movement** of membranes
* with **scattered** embedded intrinsic and extrinsic **proteins**
* membrane contains **glycoproteins**, **glycolipids**, **phospholipids** and **cholesterol**
54
Phospholipids in membranes
* Phospholipids align as a **bilayer**
* **hydrophilic** heads are attracted to water
* **hydrophobic** tails repelled by water
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Cholesterol
* Present in **eukaryotic** organisms to **restrict lateral movement** of the membranes
* adds **rigidity to membrane** – resistant to high temperatures & prevents water + dissolved ions leaking out
56
Selectively permeable membrane
* Molecules must have **specific properties** to pass through plasma membrane:
* **lipid soluble** (hormones e.g. oestrogen)
* very **small** molecules
* **non-polar** molecules (oxygen)
57
Simple diffusion
* Net movement of molecules from an area of **higher concentration to an area of lower** concentration
* until equilibrium is reached
* **passive**
58
Facilitated diffusion
* **Passive** process using protein channels/carriers
* **down the concentration gradient**
* used for **ions** and polar molecules e.g. sodium ions
* and **large** molecules e.g. glucose
59
Osmosis
* Net movement of **water**
* from an area of higher water potential to an area of lower (more negative) water potential
* across a **partially permeable membrane**
60
Water potential
* The pressure created by water molecules
* measured in **kPa** and represented by symbol **ψ**
* pure water has a water potential of 0kPa
* the more negative the water potential, the more solute must be dissolved
61
Hypertonic solution
* When the water potential of a solution is **more negative** than the cell
* water moves out of the cell by osmosis
* both animal and plant cells will **shrink** and **shrivel**
62
Hypotonic solution
* When the water potential of a solution is **more positive** (closer to zero) than the cell
* water moves **into** the cell by osmosis
* animal cells will **lyse (burst)**
* plant cells will become **turgid**
63
Isotonic
* When the water potential of the surrounding solution is the same as the water potential inside the cell
* **no net movement** in water
* cells would remain the same mass
64
Active transport
* The movement of ions and molecules from an area of lower concentration to an area of higher concentration **using ATP** and **carrier proteins**
* carrier proteins act as **selective pumps** to move substances
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Role of carrier protein in active transport
* When molecules bind to the **receptor** – **ATP** will bind to protein on **inside** of membrane and is **hydrolysed** to ATP/Pi
* protein **changes shape** and opens inside membrane
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Co-transport
* The **movement** of two substances across a membrane **together**, when one is unable to cross the membrane itself
* involves a cotransport protein
* involves active transport
* e.g. **absorption of glucose/amino acids** from lumen of intestines
67
Molecules lymphocytes identify
* **Pathogens** (bacteria, fungi, viruses)
* **cells from other organisms** of same species (transplants)
* **abnormal body cells** (tumour cells)
* **toxins** (released from bacteria)
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Antigens
* **Proteins** on the cell-surface membrane
* **trigger an immune response** when detected by lymphocytes
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Antigenic variability
* When pathogenic DNA **mutates** causing a **change in shape** of antigen
* previous immunity is no longer effective as memory cells don't **recognise** new shape of antigen
* **specific antibody** no longer binds to **new antigen**
70
Physical barriers
* **Anatomical** barriers to pathogens:
* skin
* stomach acid
* lysozymes in tears
71
Phagocytes
* **Non-specific** immune response
* phagocytes become **antigen-presenting cells** after destroying pathogen
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T lymphocytes
* Made in bone marrow and mature in **thymus** gland
* involved in **cell-mediated immune response**
* respond to antigen-presenting cells
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Antigen-presenting cells
* Any cell that presents a **non-self antigen** on their surface:
* infected body cells
* macrophage after phagocytosis
* cells of transplanted organ
* cancer cells
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Role of T helper cells
* Have **receptors** on their surface that attach to **antigens on APCs**
* become **activated** – clonal selection
75
Role of cloned T helper cells
* Some remain as helper T cells & **activate B lymphocytes**
* stimulate macrophages for **phagocytosis**
* become **memory cells** for that shaped antigen
* become **cytotoxic killer T cells**
76
Cytotoxic T cells
* Destroy abnormal/infected cells by releasing **perforin**
* so that any substances can enter or leave the cell and this causes **cell death**
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B lymphocytes
* Made in bone marrow and mature in bone marrow
* involved in **humoral immune response**
* involves **antibodies**
78
Humoral response
* APC activates B cell
* B cell undergoes **clonal selection and expansion** – rapid division by mitosis
* **differentiate** into **plasma cells/memory B cells**
* plasma cells make **antibodies**
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B memory cells
* derived from B lymphocytes
* remember **specific antibody** for particular antigen
* will rapidly **divide by mitosis** and differentiate in plasma cells upon secondary encounter
* resulting in **large numbers of antibodies rapidly**
80
Antibodies
* **Quaternary** structure proteins made of **four polypeptide chains**
* different shaped binding site = **variable region**
* **complementary** to a specific antigen
81
Antibody structure
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Agglutination
* Antibodies have **two binding sites** and are **flexible** – **clumps** pathogens together
* makes it easier for phagocytes to **locate** and **destroy** pathogen
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Passive immunity
* **Antibodies introduced** into body
* plasma and memory cells not made as no interaction with antigen
* **short-term** immunity
* **fast** acting
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Active immunity
* Immunity created by own immune system – **antibodies made**
* exposure to antigen
* plasma and memory cells made
* **long term immunity**
* slower acting
85
Natural active immunity
* After **direct contact** with pathogen through infection
* body **creates antibodies** and **memory cells**
86
Artificial active immunity
* Creation of antibodies and memory cells following introduction of an **attenuated pathogen** or **antigens**
* vaccination
87
Vaccinations
* Small amounts of **dead** or **attenuated** pathogens injected/ingested
* humoral response activated
* memory cells are able to **divide rapidly** into plasma cells when re-infected
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Primary Vs Secondary response
* **Primary** = first exposure to the pathogen
* longer time for plasma cell secretion & memory cell production
* for the **secondary** response, memory cells divide rapidly into plasma cells
* so a large number of antibodies made rapidly upon reinfection
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Herd immunity
* When enough of the population is **vaccinated** so pathogen is not transmitted and spread easily
* provides **protection** for those without vaccine
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Monoclonal antibodies
* A **single type of antibody** that can be isolated and cloned
* antibodies that are identical – from **one type** of **B lymphocyte**
* complementary to only **one antigen**
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Uses of monoclonal antibodies
* **Medical treatment** – targeting drugs by attaching antibody complementary to tumour cell antigen
* medical diagnosis – **pregnancy tests**
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Pregnancy test
* ELISA test which uses **3 monoclonal antibodies** and **enzymes** to test for **hCG**
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Purpose of ELISA test
* Detect the **presence** and **quantity** of an antigen
* used for medical diagnosis e.g. HIV
94
Ethical issues with monoclonal antibodies
* Requires **mice** to produce antibodies and tumour cells
* requires a full **cost-benefit analysis**
95
HIV structure
* **Core** = RNA and reverse transcriptase
* **capsid** = protein coat
* **lipid envelope** taken from hosts cell membrane
* **attachment proteins** so it can attach to Helper T cells
96
HIV replication
* Attaches to CD4 receptor on helper T cells
* protein fuses with membrane allowing **RNA + enzymes to enter**
* **reverse transcriptase** makes DNA copy and this is inserted into nucleus
* nucleus synthesises viral proteins
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Auto Immunodeficiency Syndrome (AIDs)
* When HIV has destroyed too many **T helper cells**, host is unable to produce adequate immune response to other pathogens
* host susceptible to **opportunistic infections**
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Role of antibodies in ELISA
* First antibody added is complementary to antigen in well – attaches
* second antibody with enzyme added which attaches to first antibody as complementary
* when substrate solution added enzyme can produce **colour change**
99
Why vaccines may be unsafe
* Inactive virus may become active – **viral transformation**
* non-pathogenic virus can **mutate** and harm cells
* side effects of immune response
* people may test positive for disease
100
Why are antibiotics ineffective against viruses?
* Viruses are **inside host cells** where antibiotics cannot reach
* antibiotics affect parts of bacteria that viruses do not have (e.g. the cell wall)
101
Why do you wash well in ELISA
* Removes unbound 2nd antibodies
* otherwise enzyme may be present → colour change → **false positive**
102
Pathogens
* **Microorganisms** that **cause a disease**
* by releasing toxins or killing cells/tissues
103
Cytokinesis
* **Final stage** in the cell cycle
* when the **cytoplasm splits** in two
* creates two new cells
104
Uncontrolled mitosis
* Uncontrolled cell division can lead to the formation of **tumours** and of **cancers**
* many cancer treatments are directed at controlling the rate of cell division
105
Viral replication
* Following **injection of their nucleic acid**
* the infected host cell replicates the virus particles
106
Cell adaptations for rapid transport across membranes?
* Increase in **surface area** or membrane
* increase in the **number of protein channels and carrier molecules** in the membranes
107
Antigen-antibody complex
* When a complementary **antibody binds to an antigen**
* this clumps pathogens together (agglutination)
