Chapter 1 Flashcards

Question

Genome

Answer 1

the complete set of genes, chromosomes or genetic material present in a cell or organism - human genome consists of 21, 000 genes - all these genes are present in each cell of your body, but not all genes are active in all types of cells in the body

Answer 2

when an unspecialised cell changes and carries out a specific function in the body - cells differentiate to form different cell types due to the expression of different genes

Answer 3

a process in which unspecialised cells develop into cells w/ a more distinct structure and function - involves the expression of some genes and not others in a cell's genome

Answer 4

- at an early stage, the fertilised egg starts to divide. - up to this stage, cells in an embryo are pluripotent embryonic stem cells- they can develop into any type of body cell - although each cell has the same genome, only certain genes are expressed in certain cells and not in others - this gives rise to the synthesis of certain proteins, which can trigger specialised development of that specific cell and its descendants - so, groups of cells differentiate along different paths to form different specialised tissues of embryo - once a cell starts to differentiate, it's irreversible NB/ process of differentiation involves expression of some genes and not others in a cell's genome

Answer 5

an undifferentiated cell of a multicellular organism that can form more cells of the same type indefinitely - from which certain other kinds of cell arise by differentiation - are unspecialised cells that can give rise to a wide range of body cells by differentiating along different pathways - they retain capacity to divide indefinitely and have potential to differentiate into specialised cell types when given right stimulus - but, not all stem cells can give rise to all body cells

Answer 6

- the 8 cells of the morula- first cells formed following fertilisation - can differentiate into any type of cell including placental cells - can give rise to a complete organism

Answer 7

- embryonic stem cells of the blastocyst | - can differentiate into all body cells, but can't give rise to a whole organism

Answer 8

- umbilical cord stem cells | - can differentiate into a few closely related types of body cell

Answer 9

- can only differentiate into their associated cell type | - eg. liver stem cells can only make liver cells

Answer 10

- embryos are important sources of stem cells - once an egg has been fertilised, it starts to divide and forms totipotent cells during early stages (up until the eight-cell stage of the morula) - each cell can still develop into a full and normal organism - these cells continue to divide and develop to form the pluripotent cells of the blastocyst - from here all the specialised tissues of developing embryo are generated

Answer 11

- a disease of the eye - it's an inherited form of juvenile macular degeneration (affects a small area near the centre of the retina) - causes progressive loss of central vision, eventually leading to complete blindness - it typically appears in late childhood to early adulthood - caused by a recessive genetic mutation in gene ABCA4- causes an active transport protein on photoreceptor cells to malfunction - ultimately causes photoreceptor cells to degenerate

Answer 12

- stem cell therapy has been shown to be effective in treating Stargardt's disease - patients are given retinal cells derived from human embryonic stem cells- are injected into the retina - the inserted cells attach to the retina and become functional - hence, it may be possible to restore sight to affected individuals using stem cells

Answer 13

a type of cancer of the blood or bone marrow - is caused by high levels of abnormal white blood cells - people w/ leukemia have a higher risk of developing infections, anemia and bleeding

Answer 14

- treatment involves harvesting hematopoietic stem cells (HSCs)- multipotent stem cells - HSCs can be taken from bone marrow, peripheral blood or umbilical cord blood - HSCs may come from either the patient or from a suitable donor - patient then undergoes chemotherapy and radiotherapy to get rid of diseased white blood cells - next step involves transplanting HSCs back into the bone marrow, where they differentiate to form new healthy white blood cells

Answer 15

- embryo - umbilical cord blood - bone marrow - adult tissues

Answer 16

1. Cells may be used in cell therapy (replacing bad cells with good ones) to eliminate serious diseases or disabilities in the human population 2. Transplants can be easily obtained without requiring death of another human or inflicting any kind of pressure on normal body functioning which happens when someone donates an organ 3. The stem cells are harvested from the embryo at an early stage when embryo hasn't yet developed a nervous system and thus it is not likely to feel any pain

Answer 17

E: have a separate membrane-enclosed nucleus P: DNA of prokaryotes is freely floating in the cytoplasm. E: Eukaryotic cells have a complex system of membrane-bound organelles that divides cell into numerous enclosed regions – compartmentalisation P: do not have any membrane-bound organelles

Answer 18

- earliest and mot primitive type of cell - include bacteria and archaea - simple unicellular organisms w/ no internal compartmentalisation, no nucleus and no membrane-bound organelles - all metabolic processes occur within the cytoplasm

Answer 19

1. Cell wall: Encloses cell, protecting it and helping to maintain its shape; prevents cell from bursting in hypotonic media 2. Plasma membrane: surrounds cell, controlling movement of substances in and out of the cell. 3. Cytoplasm: medium that fills the cell and is the site of all metabolic reactions. 4. Pili: protein filaments on the cell wall that help in cell adhesion and in transferring of DNA between two cells. 5. Flagella: much longer than pili; are responsible for locomotion of the organism. Their whip-like movement propels the cell along. 6. 70S ribosomes: the sites of protein synthesis 7. Nucleoid region: controls all cell activities and reproduction of the organism - includes naked DNA- DNA not associated with proteins known as histones 8. Plasmids: small circles of DNA that carry a few genes; often these genes give cell antibiotic resistance and are used in creating genetically modified bacteria.

Answer 20

Prokaryotic cells: 70S ribosomes, smaller than those found in eukaryotic cells Eukaryotic cells: 80S ribosomes NB/ 70S and 80S refer to sedimentation rate of RNA subunits

Answer 21

- prokaryotes reproduce by binary fission to produce 2 genetically identical cells - Binary fission is a means used by prokaryotes to reproduce asexually

Answer 22

1. The chromosome is replicated semi-conservatively, beginning at the point of origin 2. Beginning with the point of origin, the two copies of DNA move to opposite ends of the cell 3. The cell elongates (grows longer) 4. The plasma membrane grows inward and pinches off to form two separate, genetically identical cells

Answer 23

- have a compartmentalised cell structure - genetic material is isolated from cytoplasm by the nucleus - include 4 kingdoms: Protoctista, Fungi, Plantae and Animalia

Answer 24

- archaea - bacteria - eukaryota

Answer 25

1. Kingdom Protoctista - unicellular organisms; or multicellular organsims wo/ specialised tissue 2. Kingdom Fungi - have a cell wall made of chitin - obtain nutrition via heterotrophic absorption 3. Kingdom Plantae - cell wall made of cellulose - obtain nutrition autotrophically via photosynthesis 4. Kingdom Animalia - no cell wall - obtain nutrition via heterotrophic ingestion

Answer 26

refers to the formation of compartments within the cell by membrane-bound organelles

Answer 27

1. Greater efficiency of metabolism as enzymes and substrates are enclosed- hence, much more concentrated, in the particular organelles responsible for specific functions 2. Internal conditions can be differentiated in a cell to maintain optimal conditions for different enzymes 3. Isolation of toxic substances away from cytoplasm eg/ storage of hydrolytic enzymes in lysosomes 4. Flexibility of changing no. and position of organelles within cell based on the cell’s requirements

Answer 28

1. Plasma membrane: controls movement of substances in and out of the cell 2. Cytoplasm: fills cell and holds all organelles- also contains enzymes that catalyse various reactions occurring within cytoplasm 3. Mitochondria: a site of cellular respiration in which ATP is generated. 4. 80S Ribosomes: sites of protein synthesis- free ribosomes produce proteins used inside the cell itself. 5. Nucleus: controls all cell and reproduction of unicellular organisms. 6. Nucleolus: part of the nucleus involved in production of ribosomes 7. Smooth endoplasmic reticulum: responsible for producing and storing lipids, including steroids. 8. Rough endoplasmic reticulum: transports protein produced by ribosomes on its surface to Golgi apparatus- usually for use outside of the cell 9. Golgi apparatus: processes and packages proteins, which are ultimately released in Golgi vesicles. 10. Vesicle: small sac transporting and releasing substances produced by cell by fusing w/ cell membrane 11. Lysosomes (absent from plant cells): contain hydrolytic enzymes and play important roles in destruction of microbes engulfed by WBC 12. Centrioles (absent from plant cells): play important role in nuclear division- help establish microtubules 13. Vacuole (absent from animal cells): helps in osmotic balance of cell and in storage of substances- may also have hydrolytic functions similar to lysosomes 14. Cell wall (absent from animal cells): protects cell, maintains its shape and prevents it from bursting in hypotonic media 15. Chloroplast (absent from animal cells): double-membrane-bound organelles; contain pigments (chlorophyll) and are responsible for photosynthesis

Answer 29

- secretes enzymes into a duct - enzymes = proteins, so exocrine cells will have a well-developed network of rER for protein synthesis - will also have a GA that produces vesicles containing these enzymes - vesicles merge w/ plasma membrane to release their contents into the small membrane

Answer 30

- contains many chloroplasts - site of photosynthesis - in plants, this tissue contains the greatest no. of chloroplasts per cell - is positioned right under the upper epidermis where it's exposed to highest amount of light - main function is to photosynthesise: producing complex organic compounds, using CO2 and water as starting materials

Answer 31

the shortest distance between 2 separate points in a microscope's filed of view that can still be distinguished as distinct objects - higher the value, lower the resolution

Answer 32

- proposed by Singer and Nicholson in 1972 - model of the cell membrane - according to this, biological membranes consist of phospholipid bilayers w/ proteins embedded in the bilayer, making the membrane look like a mosaic

Answer 33

a molecule that has both a hydrophilic and a hydrophobic part - an amphipathic phospholipid has hydrophilic and hydrophobic properties

Answer 34

- a group of proteins w/ diverse structures associated w/ cell membrane - all carry out different functions - all support the plasma membrane in carrying out its distinctive function - are all categorised as integral or peripheral depending on their position in the membrane

Answer 35

- are amphipathic (hydrophobic and hydrophilic) - permanently attached to the. membrane - are typically transmembrane

Answer 36

- are polar (hydrophilic) | - temporarily attached by non-covalent interactions and associate w/ one surface of the membrane

Answer 37

Proteins have these functions: 1. Channels – some proteins have a pore/channel that allows passive transport of substances between the inside and outside of the cell. 2. Carriers – these proteins bind to substances on one side of the membrane and then change shape to transport them to the other side - carrier proteins that use energy to change shape are termed protein pumps 3. Recognition – certain proteins help cell in differentiating between self and non-self cells- important in triggering an immune response 4. Receptors – these proteins usually span whole membrane to relay information from inside or outside of the cell 5. Enzymes – these are proteins that enhance rate of reactions that happens at the membrane level

Answer 38

- are a phospholipid and carbohydrate attached together - important in maintaining the structure of the cell membrane - helps differentiate cells between self and non-self

Answer 39

- a component of animal cell membranes, functions to maintain integrity and mechanical stability - absent in plant cells, as PM is surrounded and supported by a rigid cell wall of cellulose - an amphipathic molecule: has both hydrophilic and hydrophobic regions - its hydroxyl group is hydrophilic and aligns towards phosphate heads of phospholipids - remained or molecule is hydrophobic and asoociates w/ phospholipid tails

Answer 40

- suggested that cell membrane comprises of a lipid bilayer - where 2 layers of polar lipid molecules are arranged w/ their hydrophilic heads outward - lipid bilayer itself sandwiched between 2 protein layers on either side of the membrane - proposed following evidence from electron microscope, which showed membrane as having 3 layers - in high magnification electron micrographs, membranes appeared as 2 dark parallel lines w/ a lighter- coloured region in between - proteins appear dark in electron micrographs - phospholipids appear light - hence, it was deduced that membranes comprised two protein layers, one on either side of a phospholipid core - model gave an explanation for the membrane's effectiveness as barrier to movement of certain substances despite being very thin

Answer 41

- assumed that all membranes had identical structures, which didn't explain how different types of membranes could carry out different functions - proteins are amphipathic which makes it improbable that they would only be found in the aqueous environment on either side of the membrane rather than going through the membrane

Answer 42

Singer and Nicholson model: - fluid mosaic model replaced D-D model - suggested that proteins are individually embedded in phospholipid bilayer, rather than coating it on both sides - allowed hydrophilic portions of both proteins and phospholipids to be maximally exposed to water- resulting a stable membrane structure - it ensures that hydrophobic portions of proteins and phospholipids were in the non-aqueous environment inside the bilayer

Answer 43

movement of particles from a region of high concentration to a region of low concentration, and is the result of the random motion of particles - two types: simple and facilitated

Answer 44

1. Temperature – molecules diffuse faster if the temperature is higher 2. Surface area of membrane – an increase in surface area allows more molecules to diffuse 3. Size of particles – smaller molecules diffuse faster than larger ones 4. Concentration gradient of diffusing particles – the bigger the gradient the faster the diffusion

Answer 45

- occurs in a gas or liquid medium - only requires a concentration gradient - occurs in both living and non-living systems - if a particle is too big, it can't pass through phospholipid bilayer of membrane - ions are also repelled by hydrophobic tails in the membrane NB/ when simple diffusion fails, facilitated diffusion can transfer the particle across the membrane

Answer 46

- similar to simple diffusion, but it requires channel proteins or carrier proteins, which are specific the molecules being transported across plasma membrane - size and shape of protein carriers and channels determine what substance can cross the membrane

Answer 47

Important application: movement of K+ ions in neurons during generation of an action potential; a key step in the propagation of nerve impulses along neurons - helps in moving K+ ions out of the axons to cause repolarisation - K+ channels involved only allow movement of K+ - they're also voltage gated, they open and close w/ changes in electrical potential to control movement of K+ ions

Answer 48

the passive movement of water molecules from a region of lower solute concentration to a region of higher solute concentration across a partially permeable membrane - involves water molecules only

Answer 49

- in medical procedures, tissues need to be kept in a saline solution for storage - it's essential that osmolarity of saline solution is same as that in the cytoplasm of the cells of the tissue to prevent any osmosis that would damage the cells

Answer 50

refers to concentration of a solution in terms of moles of solutes per litre of solution

Answer 51

- solution has relatively lower osmolarity | - low solute conc. = loses water

Answer 52

- solutions w/ a relatively higher osmolarity | - high solute conc. = gains water

Answer 53

when the concentrations of solutes are equal inside and outside of the cell, so there is no net movement of water

Answer 54

- movement of particles across membranes, requiring energy in the form of ATP - energy is used to move substances against a concentration gradient, from a region of low concentration to one of a higher concentration

Answer 55

1. When the pump is open to the inside of the axon, 3 sodium ions (Na+) enter the pump and attach to their binding sites 2. ATP donates a phosphate group to the pump 3. This causes protein to change shape expelling Na+ to the outside 4. 2 potassium ions (K+) from outside then enter and attach to their binding sites. 5. Binding of K+ leads to release of the phosphate, causes pump to change shape again so that it's only open to the inside of the axon 6. K+ is released inside. 7. Na+ can now enter and bind to the pump again

Answer 56

a cellular process where cells take in molecules or substances from outside of the cell by engulfing them in the cell membrane - can be divided into pinocytosis and phagocytosis - possible due to the fluidity of membranes

Answer 57

involves the ejection of waste products or useful substances from the inside of the cell - can be divided into excretion and secretion - possible due to the fluidity of membranes

Answer 58

the taking in of liquid substances by cells | - type of endocytosis

Answer 59

involves the absorption of solids - type of endocytosis - eg. when a WBC or phagocyte engulfs a pathogenic microbe

Answer 60

Can be divided into: 1. Excretion: following phagocytosis, any undigested remains of the microbe that aren't useful to the cell are excreted outside the cell 2. Secretion: Proteins synthesised by ribosomes on rER are first passed to GA via vesicles - here they're processed and packaged before being released in vesicles that fuse w/ the plasma membrane for secretion outside the cell

Answer 61

- play an important role in exocytosis and endocytosis, allow movement of materials within the cell - many of the organelles in the cell are membrane-bound; they can make their own vesicles - vesicles are a common way for cell to move molecules around inside cells

Answer 62

1. Enzymes are made by bound ribosomes in rough ER 2. Rough ER will package enzymes in a vesicle formed from membranes of rough ER 3. Vesicles carrying enzymes will move to Golgi apparatus, and fuse w/ Golgi apparatus membrane 4. Enzymes will be modified further in Golgi apparatus and then packed in a vesicle created using Golgi apparatus membrane 5. Vesicle will then move to the plasma membrane and undergo exocytosis and release enzymes out of cell

Answer 63

- Louis Pasteur provided crucial evidence to support the hypothesis that cells must come from pre-existing cells - his experiment disproved theory of spontaneous generation - Pasteur hypothesised that cells must come from cells and designed a falsifiable experiment

Answer 64

Stated that life could appear from a combination of dust, air and other factors

Answer 65

1. Boiled nutrient broth in 3 swan-neck flasks 2. He then broke the neck of one flask to allow air to enter, but left other flask unbroken 3. Broth in flask where swan neck wasn't broken remained clear - no microbes were formed - any microbes from the air were trapped in the curve of the swan neck 4. Broth in the broken-necked flask became cloudy - microbes carried to flask in air grew and multiplied 5. In the third flask, Pasteur tilted the flask to expose the broth to the microbes in the curve of the swan neck His experiments proved that spontaneous generation of cells and organisms doesn't occur on Earth - showed that the present conditions don't sustain the process

Answer 66

First cell must have come from non-living material | - this has gained support from evidence collected in the Miller-Urey experiment

Answer 67

1. Recreated conditions of early Earth in a closed system - included a reducing atmosphere (low oxygen) w/ high radiation levels, high temp. and electrical storms 2. After running experiment for a week, some simple AA and complex oily hydrocarbons were found in reaction mixture 3. This experiment proved that non-living synthesis of simple organic molecules was possible

Answer 68

1. Simple organic molecules, eg. amino acids, fatty acids and carbohydrates, must be formed 2. Larger organic molecules eg. phospholipids, RNA and DNA, must be assembled from simpler molecules 3. Organisms reproduce, so replication of nucleic acids must be possible 4. Biochemical reactions require set conditions, eg. pH - hence, self-contained structures, eg. membranes are necessary.

Answer 69

Explains origin of eukaryotic cells - it's highly probable that the first cells were prokaryotic in structure and appearance - proof lies in double membrane structure of organelles eg. mitochondria and chloroplasts - also comparison of DNA of those organelles w/ prokaryotic genomes

Answer 70

- supports idea that mitochondria and chloroplasts themselves were prokaryotes that were taken in by larger prokaryotes by endocytosis - instead of being digested and broken down, these cells remained inside the host cells - cells that could carry out aerobic respiration and thus provide energy to host cell, probably anaerobes who didn't need oxygen, evolved into mitochondria - prokaryotic cells that could convert light energy to chemical energy (probably cyanobacteria) became chloroplasts and passed on sugars produced during photosynthesis to the host cell

Answer 71

Both mitochondria and chloroplasts: - Have double membranes, as expected for cells taken in by endocytosis - Have singular naked DNA, as in prokaryotes - Have 70S ribosomes, as in prokaryotes - Divide by binary fission like prokaryotic cells - Are susceptible to some antibiotics

Answer 72

1. Interphase 2. Mitosis 3. Cytokinesis

Answer 73

- most active and the longest phase of the cell cycle - cells spend most of their life within this stage undergoing common cell processes eg/ metabolism, endocytosis, exocytosis and using and obtaining nutrients - it involves many processes that occur both in nucleus and cytoplasm - It has 3 important phases of cell cycle: G1 (Gap 1), S (synthesis), and G2

Answer 74

1. Gap 1 (G1) - happens in the cytoplasm - cell grows and functions normally, undergoing everyday processes - Rapid protein synthesis takes place allowing cell to grow in size - Proteins required for DNA synthesis (the next phase) are made 2. DNA Synthesis (S) - happens in the nucleus - amount of DNA doubles as DNA replication takes place - genetic material is duplicated but no chromosomes are formed yet 3. Gap 2 (G2) - happens in the cytoplasm - protein synthesis occurs to produce proteins needed for cell division, such as microtubule proteins that will make up a mitotic spindle- cell is actively preparing for cell division - mitochondria and chloroplasts (plant cells) are replicated

Answer 75

division of nucleus into 2 genetically identical daughter nuclei - involves separation of sister chromatids into individual chromosomes - these are then distributed among daughter nuclei

Answer 76

- once mitosis has been completed, w/ formation of 2 nuclei w/ identical sets of chromosomes, cell enters cytokinesis - in cytokinesis, cytoplasm of a parental cell is divided between 2 daughter cells

Answer 77

- a family of proteins that control progression of cells through the cell cycle - cells can't progress to next stage of cell cycle unless specific cyclin reaches a certain conc. - cyclins bind to cyclin-dependent kinases (CDKs) and activate them - activated CDKs then attach phosphate groups to other proteins in the cell - attachment of phosphate triggers other proteins to become active and carry out tasks; in this case, specific to phases of the cell cycle - cyclins and CDKs regulate the cell cycle - depending on presence and action of these proteins, cell cycle can be fast or slow, and it may even stop altogether

Answer 78

Mutations in genes that code for cyclins can lead to problems regulating the cell cycle, which may lead to cancer

Answer 79

G1 phase: During this phase cyclin D (red line) levels gradually increase S phase: Cyclin E is instrumental to DNA replication and also promotes centromere duplication G2 phase: Cyclin A helps induce DNA replication Mitosis: Cyclin B is essential for formation of mitotic spindles and alignment of chromatids

Answer 80

- the division of the nucleus - involves separating the DNA that was replicated in the S phase - in eukaryotic cells, this is done through the formation of chromosomes

Answer 81

- consist of DNA which is tightly wound around proteins called histones - histones are basic (alkaline) proteins that form part of nucleosomes - many nucleosomes are coiled together in a specific pater to form the chromosome - during interphases, chromosomes are unpacked, so protein synthesis and replication can take place - DNA is only visible during mitosis - DNA is initially packaged by histones to form chromatin, which undergoes further condensation to form chromosome - hence, chromatin is a lower order of DNA organisation, chromosomes are a higher order of DNA organisation

Answer 82

1. During interphase, DNA is present as chromatin 2. Following prophase, phase when DNA supercoiling takes place, DNA is visible as a pair of sister chromatids that are identical to each other connected by a centromere 3. After sister chromatids are separated during anaphase, they are referred to as chromosomes

Answer 83

Mitosis occurs after the G2 phases - it involves four phases (PMAT) 1. Prophase 2. Metaphase 3. Anaphase 4. Telophase

Answer 84

- DNA supercoils causes chromatin to condense - Nucleolus disappears - Nuclear membrane disintegrates - Spindle fibres (made of microtubules) start to form (and are completely formed by end of prophase) - Centrioles (absent from plant cells) move to opposite poles

Answer 85

- Spindle fibres bind to centromere of sister chromatids and cause their movement towards equatorial plate - Sister chromatids are aligned at equatorial plate at end of metaphase

Answer 86

- Sister chromatids are separated (now known as chromosomes) and pulled to opposite poles by spindle fibres

Answer 87

- Chromosomes have reached the poles - A nuclear membrane starts to reform at each pole - A nucleolus appears in each new nucleus - The spindle fibres disintegrate - The cell elongates in preparation for cytokinesis - In some cases, invagination of membrane is also visible (marking the beginning of cytokinesis)

Answer 88

the ratio of the no. of cells in a population undergoing mitosis (prophase, metaphase, anaphase or telophase) to the total no. of visible cells - indicates how many cells in a tissue are dividing at a given time - In a tumour, where cell division is uncontrolled, mitotic index is higher than in normal tissue - hence, mitotic index is used to predict how quickly a cancer could spread and likely outcome in reducing cell proliferation of any treatment eg. chemotherapy

Answer 89

Mitotic index= (P+M+A+T)/ Total cells P, M, A and T= refer to no. of cells at each phase

Answer 90

the division of the parental cytoplasm between the two daughter cells after mitosis (it often starts in telophase) - for animal and plant cells, cytokinesis is very different due to the presence of a cell wall in plant cells

Answer 91

1. A ring of protein (microfilaments) located immediately beneath plasma membrane at the equator pulls plasma membrane inward 2. The inward pull on plasma membrane produces the characteristic cleavage furrow 3. When cleavage furrow reaches centre of the cells, it is pinched apart to form two daughter cells

Answer 92

1. Golgi apparatus forms vesicles that consist of material to build a new cell wall 2. Vesicles merge and form the cell plate 3. Cell plate grows and divides into two daughter cells

Answer 93

formation of a tumour (or several of them)

Answer 94

a mass of cells that divide uncontrollably - there are two types: benign and malignant - not all tumours lead to cancer

Answer 95

- usually localised - doesn't spread to other parts of the body - most benign tumour respond well to treatment

Answer 96

- a cancerous growth that's often resistant to treatment - it may spread to other parts of the body - may also sometimes recur after it has been removed

Answer 97

When the events of the cell cycle are disrupted because of a mutation in one of the cyclins, CDKs, or a protein associated with the cell cycle - eg/ p53 is a protein involved in regulation of the cell cycle - a mutation in the p53 gene can lead to tumour formation - over 50% of all tumours have a mutation in p53 gene - a mutation in a single cell can trigger beginning of a tumour - cell may have lost its ability to enter G1-phase, and instead continues to divide rapidly - mutation is passed on to daughter cells and a clump of cells starts to form - When this uncontrolled growth continues, a tumour is formed

Answer 98

a change in an organism's genetic code - a change in base sequence of a certain gene can result in tumour formation - some parts of a gene don't code for anything, so a mutation in these areas won't affect the organism - not all gene mutations lead to uncontrolled cell division

Answer 99

- agents that cause gene mutations - not all mutations result in cancers - anything that causes a mutation has the potential to cause a cancer

Answer 100

- Chemicals that cause mutations, referred to as carcinogens, eg/ asbestos or dioxin. - High-energy radiation, such as X-rays - Short-wave UV light - Some viruses eg/ hepatitis B.

Answer 101

a mutated gene that contributes to development of a tumour - in their normal, un-mutated state, oncogenes are called proto-oncogenes - help in regulation of cell division

Answer 102

- Once abnormal cell division has started at a particular place in the body, a malignant primary tumour begins to form - If left untreated, this may follow a particular development pathway to form secondary tumours - the tumour has metastasised`

Answer 103

1. Cancerous cells detach from primary tumour 2. Some cancerous cells gain ability to penetrate walls of lymph or blood vessels and so circulate around the body 3. Circulating cancerous cells invade tissues at different locations and develop, by uncontrolled cell division, into secondary tumours

Answer 104

the movement of cells from a primary tumour to other parts of the body where they develop into secondary tumours

Answer 105

- made of more that one cell - have properties that emerge from the interaction of their cellular components - specialised tissues can develop by cell differentiation in multicellular organisms - cells may be grouped together to form tissues - functional grouping of multiple tissues forms organs - organs interact to form organ systems, carry out specificy body functions - organ systems collectively carry out the life function of the complete organism

Answer 106

- Unlimited growth potential- can differentiate into any type in the body - More risk of becoming tumour cells than adult stem cells - Less chance of genetic damage due to accumulation of mutations than with adult stem cells - Likely to be genetically different from an adult patient receiving the tissue - Removal of cells from the embryo kills it

Answer 107

- Easily obtained and stored- commercial collection and storage services already available - Fully compatible with tissues of adult that grows from baby- no rejection problems - Limited capacity to differentiate into different cells types- only naturally develop into blood cells - Limited quantities of stem cells from one baby’s cord - Umbilical cord is discarded whether or not stem cells are taken from it

Answer 108

- Difficult to obtain as there are few of them and are buried deep in tissues - Less growth potential than embryonic stem cells - Less chance of malignant tumours developing than from embryonic stem cells - Limited capacity to differentiate into different cell types - Fully compatible with the adult’s tissue- no rejection problems - Removal of stem cells doesn’t kill the adult from which the cells are taken

Answer 109

D-D model of membrane structure was accepted by cell biologists for about 30 years - Results of many experiments fitted model including X-ray diffraction studies and electron microscopy 1950’s and 60’s: experimental evidence accumulated that didn’t fit the D-D model Freeze-etched electron micrographs - Involves rapid freezing of cells and then fracturing them - Fracture occurs along lines of weakness, including centre of membranes - Globular structures scattered through freeze-etched images of centre of membranes were interpreted as transmembrane proteins Structure of membrane proteins - Improvements in biochemical techniques allowed proteins to be extracted from membranes - Found to be varied in size and globular in shape- unlike type of structural protein that would form continuous layers on membrane periphery - Proteins were hydrophobic on part of surface so they’d be attracted to hydrocarbon tails of phospholipids in membrane centre Fluorescent antibody tagging - Red or green fluorescent markers were attached to antibodies that bind to membrane proteins - Membrane proteins of some cells were tagged with red markers and others with green markers - The cells were fused together - Within 40 minutes red and green markers were mixed throughout membrane of fused cell - showed that membrane proteins are free to move within membrane rather than being fixed in a peripheral layer This experimental evidence falsified D-D model - A replacement was needed that fitted evidence – Singer- Nicolson fluid mosaic model

Answer 110

1930’s: Davson and Danielli- layers of protein adjacent to phospholipid bilayer on both sides of membrane - Proposed this as they thought it would explain how membranes, despite being very thin, are an effective barrier to movement of substances 1950’s: high magnification electron micrographs of membranes were made - Showed two dark lines with a lighter band between - Proteins appear darker in electron micrographs and phospholipids appear light- this fitted Davson and Danielli model

Answer 111

- consists of integral proteins w/ a hydrophilic inner pore via which potassium ions may be transported - channel is comprised of four transmembrane subunits, while the inner pore contains a selectivity filter at its narrowest region that restricts passage of alternative ions - Potassium channels are typically voltage-gated and cycle between an opened and closed conformation depending on the transmembrane voltage

Answer 112

Carrier Proteins - integral glycoproteins that bind a solute and undergo a conformational change to translocate solute across membrane - only bind a specific molecule via an attachment similar to an enzyme-substrate interaction - may move molecules against conc. gradients in presence of ATP (i.e. are used in active transport) - much slower rate of transport than channel proteins Channel Proteins - Integral lipoproteins that contain a pore via which ions may cross from one side of membrane to the other - are ion-selective and may be gated to regulate passage of ions in response to certain stimuli - only move molecules along a conc. gradient (i.e. are not used in active transport) - have a much faster rate of transport than carrier proteins

Answer 113

- osmolarity of a tissue is interpolated by bathing sample in solutions w/ known osmolarities - tissue will lose water when placed in hypertonic solutions - tissue will gain water when placed in hypotonic solutions - water loss or gain may be determined by weighing sample before and after bathing in solution - Tissue osmolarity is inferred by identifying conc. of solution at which there is no weight change (i.e. isotonic)

Answer 114

Uncontrolled osmosis will have negative effects with regards to cell viability: - Hypertonic solutions: water will leave the cell causing it to shrivel (crenation) - Hypotonic solutions: water will enter the cell causing it to swell and potentially burst (lysis)

Answer 115

In plant tissues, effects of uncontrolled osmosis are moderated by the inflexible cell wall - Hypertonic solutions: cytoplasm will shrink (plasmolysis) but cell wall will maintain a structured shape - Hypotonic solutions: cytoplasm will expand but is unable to rupture within the constraints of the cell wall (turgor)

Answer 116

Cells need to produce chemical energy (via metabolism) to survive - requires exchange of materials w/ the environment Rate of metabolism of a cell: - a function of its mass / volume - larger cells need more energy to sustain essential functions Rate of material exchange: - a function of its surface area - large membrane surface = more material movement

Answer 117

Cells and tissues specialised for gas or material exchanges will increase surface area to optimise material transfer 1. Intestinal tissue of digestive tract has villi to increase surface area of inner lining 2. Alveoli in lungs have membranous extensions- microvilli, that function to increase total membrane surface

Answer 118

When a cell differentiates and becomes specialised, it loses its capacity to form alternative cell types Stem cells are unspecialised cells that have two key qualities: 1. Self Renewal – they can continuously divide and replicate 2. Potency – have the capacity to differentiate into specialised cell types

Answer 119

1. Cytoplasm – internal fluid component of cell 2. Nucleoid – region of cytoplasm where DNA is located (DNA strand is circular and called a genophore) 3. Plasmid – autonomous circular DNA molecules that may be transferred between bacteria (horizontal gene transfer) 4. Ribosomes – complexes of RNA and protein responsible for polypeptide synthesis (prokaryote ribosome = 70S) 5. Cell membrane – Semi-permeable and selective barrier surrounding the cell 6. Cell wall – rigid outer covering made of peptidoglycan; maintains shape and prevents bursting (lysis) 7. Slime capsule – a thick polysaccharide layer used for protection against dessication and phagocytosis 8. Flagella – Long, slender projections w/ a motor protein that enables movement 9. Pili – Hair-like extensions that enable adherence to surfaces (attachment pili) or mediate bacterial conjugation (sex pili)

Answer 120

- found in prokaryotes and eukaryotes 1. Ribosomes Function: site of polypeptide synthesis (translation) Structure: two subunits made of RNA and protein; larger in eukaryotes (80S) than prokaryotes (70S) 2. Cytoskeleton Function: Provides internal structure and mediates intracellular transport (less developed in prokaryotes) Structure: A filamentous scaffolding within cytoplasm (fluid portion of cytoplasm = cytosol) 3. Plasma membrane Function: Semi-permeable and selective barrier surrounding the cell Structure: Phospholipid bilayer embedded with proteins (not an organelle per se, but a vital structure)

Answer 121

1. Nucleus Structure: Double membrane structure w/ pores; has a nucleolus Function: Stores genetic material (DNA) as chromatin; nucleolus is site of ribosome assembly 2. Endoplasmic Reticulum Structure: A membrane network that may be bare (smooth ER) or studded w/ ribosomes (rough ER) Function: Transports materials between organelles (smooth ER = lipids ; rough ER = proteins) 3. Golgi Apparatus Structure: An assembly of vesicles and folded membranes located near cell membrane Function: Involved in sorting, storing, modification and export of secretory products 4. Mitochondrion Structure: Double membrane structure, inner membrane highly folded into internal cristae Function: Site of aerobic respiration (ATP production) 5. Peroxisome Structure: Membranous sac containing a variety of catabolic enzymes Function: Catalyses breakdown of toxic substances (e.g. H2O2) and other metabolites 6. Centrosome Structure: Microtubule organising centre (contains paired centrioles in animal cells but not plant cells) Function: Radiating microtubules form spindle fibres and contribute to cell division (mitosis / meiosis)

Answer 122

1. Chloroplast Structure: Double membrane structure w/ internal stacks of membranous discs (thylakoids) Function: Site of photosynthesis – manufactured organic molecules are stored in various plastids 2. Vacuole (large and central) Structure: Fluid-filled internal cavity surrounded by a membrane (tonoplast) Function: Maintains hydrostatic pressure (animal cells may have small, temporary vacuoles) 3. Cell Wall Structure: External outer covering made of cellulose (not an organelle per se, but a vital structure) Function: Provides support and mechanical strength; prevents excess water uptake

Answer 123

Lysosome Structure: Membranous sacs filled w/ hydrolytic enzymes Function: Breakdown / hydrolysis of macromolecules

Answer 124

Advantages of electron microscopes: 1. Have a much higher range of magnification (can detect smaller structures) 2. Have a much higher resolution (can provide clearer and more detailed images) Disadvantage: can't display living specimens in natural colours`

Answer 125

1. Mitochondria – Cells w/ many mitochondria typically undertake energy-consuming processes (e.g. neurons, muscle cells) 2. ER – Cells w/ extensive ER networks undertake secretory activities (e.g. plasma cells, exocrine gland cells) 3. Lysosomes – Cells rich in lysosomes undertake digestive processes (e.g. phagocytes) 4. Chloroplasts – Cells w/ chloroplasts undergo photosynthesis (e.g. plant leaf tissue but not root tissue)

Answer 126

- Consist of a polar, hydrophilic head composed of a glycerol and a phosphate molecule - Consist of two non-polar hydrophobic tails composed of fatty acid (hydrocarbon) chains - as phospholipids have both hydrophilic and lipophilic (hydrophobic) regions, they are classed as amphipathic

Answer 127

- Phospholipids spontaneously arrange into a bilayer - hydrophobic tail regions face in and are shielded from surrounding polar fluids - the 2 hydrophilic head regions associate w/ cytosolic and extracellular fluids

Answer 128

- bilayer is held together by weak hydrophobic interactions between the tails - Hydrophilic / hydrophobic layers restrict passage of many substances - Individual phospholipids can move within bilayer, allowing for membrane fluidity and flexibility - This fluidity allows for spontaneous breaking and reforming of membranes (endocytosis / exocytosis)

Answer 129

JET RAT 1. Junctions – Serve to connect and join two cells together 2. Enzymes – Fixing to membranes localises metabolic pathways 3. Transport – Responsible for facilitated diffusion and active transport 4. Recognition – May function as markers for cellular identification 5. Anchorage – Attachment points for cytoskeleton and extracellular matrix 6. Transduction – Function as receptors for peptide hormones

Answer 130

Phospholipid bilayers are fluid= phospholipids are in constant movement relative to one another Cholesterol interacts w/ the fatty acid tails of phospholipids to moderate properties of the membrane: 1. Cholesterol functions to immobilise outer surface of membrane, reducing fluidity 2. It makes membrane less permeable to very small water-soluble molecules that would otherwise freely cross 3. It functions to separate phospholipid tails and so prevent crystallisation of membrane 4. It helps secure peripheral proteins by forming high density lipid rafts capable of anchoring the protein

Answer 131

Active transport uses energy to move molecules against a conc. gradient This energy may either be generated by: - Direct hydrolysis of ATP (primary active transport) - Indirectly coupling transport w/ another molecule that's moving along its gradient (secondary active transport)

Answer 132

- a specific solute will bind to protein pump on one side of the membrane - hydrolysis of ATP (to ADP + Pi) causes a conformational change in protein pump - solute molecule is consequently translocated across membrane (against gradient) and released

Answer 133

Endoplasmic reticulum is a membranous network that's responsible for synthesising secretory materials - Rough ER: embedded w/ ribosomes and synthesises proteins destined for extracellular use - Smooth ER is involved in lipid synthesis and plays a role in carbohydrate metabolism

Chapter 1 Flashcards

Cell biology