biology 1 fry

Question 1

List what a cell needs to do to survive

Answer 1

1) need to import food and gases 2) needs to control changes in pH and temperature generated by reactions 3) deal with waste products 4) all reactions need to be carried out under mild conditions

Question 2

Who discovered the cell?

Answer 2

Robert Hooke in 1665

Question 3

Compare and contrast light microscopes and electron microscopes

Answer 3

Light microscope:1) 1mm -100nm size range 2) resolution 200nm3) can see cell processes in real time - mitosis and meiosis 4) sample can still be alive Electron microscope 1) 100 um - 1nm 2) damaging to the cell 3) vacuum and expensive equipment 4) a lot of manipulation so “artefacts” can emerge 5) specialist training required to stain samples 6) higher magnification and resolution

Question 4

Compare and contrast eukaryotic and prokaryotic cells

Answer 4

Prokaryotic 1) no clear nucleus and therefore no nuclear envelope or nucleolus 2) mitochondria never present 3)Endoplasmic reticulum never present 4) cytoskeleton not present 5) circular DNA not associated with histone proteins 6) cell wall made of peptidoglycan always present 7) unicellular 8) 1-10 um 9) 1um3 cell volume Eukaryotic1) nucleus usually present surrounded by a nuclear envelope and containing a nucleolus 2) mitochondria usually present 3) ER always present 4) cytoskeleton always present made up of microtubules and microfilaments 5) chromosomes - DNA arranged in several long strands associated with histones 6) cell wall present in plants made of cellulose 7) multicellular 8) 10m- 100um 9) 1000um3 cell volume

Question 5

Discuss why the surface area to volume ratio of a cell is important to a cells survival

Answer 5

1) as an organism gets bigger both its surface area and volume increase2) as volume increases the surface area to volume ratio decreases , so it needs to find ways of increasing its surface area so it can exchange substances with the environment 3) in bacteria diffusion is the main mode of transport this would be too slow if the surface area to volume ratio was small

Question 6

What is compartmentalisation

Answer 6

The formation of cellular compartments- mitochondria, chloroplasts , Golgi, ER - different reactions occur in each section -if there was no organisation in eukaryotic cells the required chemical reactions would occur much slower in eukaryotes than they do in prokaryotes

Question 7

Explain why cells are compartmentalised

Answer 7

1) to make the chemistry work more efficiently 2) organised by function - division of labour 3) cells divided by boundaries - membranes 4) Compartmentalization allows each compartment to perform specific functions without interference from other cell functions. For example, lysosomes can break down cell debris in a compartment without accidentally digesting the cell itself.5)It also allow enzymes and substrates to reach higher concentrations than if everything was diluted by the entire cytoplasm. For example, the mitochondria accumulates a large electron gradient in order for the electron transport chain to work.

Question 8

Outline the fluid mosaic mode

Answer 8

The Fluid Mosaic Model states that membranes are composed of a Phospholipid Bilayer with various protein molecules floating around within it. The ‘Fluid’ part represents how some parts of the membrane can move around freely, if they are not attached to other parts of the cell. The ‘mosaic’ part illustrates the ‘patchwork’ of proteins that is found in the Phospholipid Bilayer.Some proteins in the membrane are called ‘Intrinsic’. This means that they completely span the Bilayer. Others are called ‘Extrinsic’ - they are partly embedded in the Bilayer.

Question 9

Describe the composition of cell membranes

Answer 9

1) monolayer is made of - phospholipids with a hydrophobic tail and a hydrophilic head 2) composed of amphipathic phospholipids - different characteristics 3) Bilayer- made of phospholipids - energetically favourable 4) glycoproteins- recognition sites/ receptor sites 5) cholesterol in the bilayer helps to regulate fluidity 6) proteins in the membranes can form channels to allow substances to diffuse through 7) made up of glycerol, 2 fatty acid tails , and phosphate

Question 10

What is the role of the nucleus

Answer 10

1) protects DNA- isolates it from danger 2) gated pores to allow nuclear signals to get in 3) 1-3um 4) The nucleus is surrounded by two membranes with a small gap between them. The pair of membranes is known as the nuclear envelope. There are small gaps all over the envelope, called nuclear pores5) site of cellular DNA storage, replication and transcription6) enzymes used in the nucleus are made in the cytosol 7) DNA and histone proteins form chromatin

Question 11

What are ribosomes

Answer 11

1) made of lots of RNA 2) found free in the cytosol or attached to rough ER 3) not an organelle because they do not have a membrane 4) site of DNA translation

Question 12

What is the Golgi

Answer 12

1) decides where proteins should be moved in a cell 2) packages and modifies proteins into vesicles 3) vesicles need to dock back or the Golgi will bud out 4) recognises molecular postcodes 5) high turnover unlike ER 7) has a Cis side for receiving proteins and a Trans side for shipping them

Question 13

What is ER?

Answer 13

1) rough ER associated with nucleus 2) site of translation of proteins destined for membrane or secretion 3) space inside it is called the lumen Smooth ER 1) no ribosomes 2) involved in carbohydrates metabolism 3) drug metabolism ion movement4) sarcoplasmic reticulum has a lot of Ca2+ ions 5) transport vesicles bud off the ER and migrate to the Golgi

Question 14

What is the cytoskeleton

Answer 14

1) not an organelle because it’s not membrane bound 2) shapes cell 3) contains microvilli, microtubules the biggest 25 nm , actin smallest globular 7nm , intermediately filaments 4) move mitochondria around by forming tracts , also move chromosomes etc 5) makes connective tissue which holds cells together

Question 15

Outline the role of mitochondria

Answer 15

1) apoptosis , aerobic respiration , ATP synthesis 2) proton gradients

Question 16

What are peroxisomes

Answer 16

1) contain oxidative enzymes that produce hydrogen peroxide as a toxic byproduct which they then inactivate with catalase .2) catalase breaks down hydrogen peroxide

Question 17

What are lysosomes

Answer 17

1) low pH 2) digestive enzyme 3) autophagy- a process by which cells digest bits of themselves

Question 18

List what a cell needs to do to survive (4)

Answer 18

1) need to import food and gases 2) needs to control changes in pH and temperature generated by reactions 3) deal with waste products 4) all reactions need to be carried out under mild conditions

Question 19

Compare and contrast eukaryotic and prokaryotic cells (18)

Answer 19

Prokaryotic 1) no clear nucleus and therefore no nuclear envelope or nucleolus 2) mitochondria never present 3)Endoplasmic reticulum never present 4) cytoskeleton not present 5) circular DNA not associated with histone proteins 6) cell watt made of peptidoglycan always present 7) unicellular 8) 1-10 um 9) 1um3 cell volume Eukaryotic1) nucleus usually present surrounded by a nuclear envelope and containing a nucleolus 2) mitochondria usually present 3) ER always present 4) cytoskeleton always present made up of microtubules and microfilaments 5) chromosomes - DNA arranged in several long strands associated with histones 6) cell wall present in plants made of cellulose 7) multicellular 8) 10m- 100um 9) 1000um3 cell volume

Question 20

Compare and contrast light microscopes and electron microscopes (10)

Answer 20

Light microscope:1) 1mm -100nm size range 2) resolution 200nm3) can see cell processes in real time - mitosis and meiosis 4) sample can still be alive Electron microscope 1) 100 um - 1nm 2) damaging to the cell 3) vacuum and expensive equipment 4) a lot of manipulation so “artefacts” can emerge 5) specialist training required to stain samples 6) higher magnification and resolution

Question 21

Discuss why the surface area to volume ratio of a cell is important to a cells survival (3)

Answer 21

1) as an organism gets bigger both its surface area and volume increase2) as volume increases the surface area to volume ratio decreases , so it needs to find ways of increasing its surface area so it can exchange substances with the environment 3) in bacteria diffusion is the main mode of transport this would be too slow if the surface area to volume ratio was small

Question 22

Explain why cells are compartmentalised (5)

Answer 22

1) to make the chemistry work more efficiently 2) organised by function - division of labour 3) cells divided by boundaries - membranes 4) Compartmentalization allows each compartment to perform specific functions without interference from other cell functions. For example, lysosomes can break down cell debris in a compartment without accidentally digesting the cell itself.5)It also allow enzymes and substrates to reach higher concentrations than if everything was diluted by the entire cytoplasm. For example, the mitochondria accumulates a large electron gradient in order for the electron transport chain to work.

Question 23

Describe the composition of cell membranes (7)

Answer 23

1) monolayer is made of - phospholipids with a hydrophobic tail and a hydrophilic head 2) composed of amphipathic phospholipids - different characteristics 3) Bilayer- made of phospholipids - energetically favourable 4) glycoproteins- recognition sites/ receptor sites 5) cholesterol in the bilayer helps to regulate fluidity 6) proteins in the membranes can form channels to allow substances to diffuse through 7) made up of glycerol, 2 fatty acid tails , and phosphate

Question 24

What is the role of the nucleus (7)

Answer 24

1) protects DNA- isolates it from danger 2) gated pores to allow nuclear signals to get in 3) 1-3um 4) The nucleus is surrounded by two membranes with a small gap between them. The pair of membranes is known as the nuclear envelope. There are small gaps all over the envelope, called nuclear pores5) site of cellular DNA storage, replication and transcription6) enzymes used in the nucleus are made in the cytosol 7) DNA and histone proteins form chromatin

Question 25

What are ribosomes (4)

Answer 25

1) made of lots of RNA 2) found free in the cytosol or attached to rough ER 3) not an organelle because they do not have a membrane 4) site of DNA translation

Question 26

What is ER (8)

Answer 26

1) rough ER associated with nucleus 2) site of translation of proteins destined for membrane or secretion 3) space inside it is called the lumen Smooth ER 1) no ribosomes 2) involved in carbohydrates metabolism 3) drug metabolism ion movement4) sarcoplasmic reticulum has a lot of Ca2+ ions 5) transport vesicles bud off the ER and migrate to the Golgi

Question 27

What is the Golgi (7)

Answer 27

1) decides where proteins should be moved in a cell 2) packages and modifies proteins into vesicles 3) vesicles need to dock back or the Golgi will bud out 4) recognises molecular postcodes 5) high turnover unlike ER 7) has a Cis side for receiving proteins and a Trans side for shipping them

Question 28

What is the cytoskeleton (5)

Answer 28

1) not an organelle because it’s not membrane bound 2) shapes cell 3) contains microvilli, microtubules the biggest 25 nm , actin smallest globular 7nm , intermediately filaments 4) move mitochondria around by forming tracts , also move chromosomes etc 5) makes connective tissue which holds cells together

Question 29

Outline the role of mitochondria (2)

Answer 29

1) apoptosis , aerobic respiration , ATP synthesis 2) proton gradients

Question 30

What are lysosomes (3)

Answer 30

1) low pH 2) digestive Genzyme 3) aurophagy- a process by which cells digest bits of themselves

Question 31

What are peroxisomes (2)

Answer 31

1) contain oxidative enzymes that produce hydrogen peroxide as a toxic by-product which they then inactivate with catalase .2) catalase breaks down hydrogen peroxide

Question 32

explain how lysosomes are formed

Answer 32

1) In the nucleus, a small piece of the DNA codes for the production of inactive hydrolytic lysosomal enzymes. The DNA code is transcribed into messenger RNA. 2) The mRNA leaves the nucleus via the nuclear pores and attaches to the rough ER ribosomes. 3) The ribosome translates the mRNA into a protein which is eventually pinched off to form RER transport vesicles.4) The RER transport vesicles containing the inactive lysosomal enzymes fuse with the Golgi apparatus membranes and release the enzymes into the Golgi apparatus5) Within the Golgi apparatus lysosomal enzymes are modified and activated.6) the enzymes are packaged into membrane bound organelles called lysosomes which are released into the cytoplasm

Question 33

explain how the first living cells appeared

Answer 33

1) Abiotic (nonliving synthesis of small organic molecules such as amino acids and nucleotides.2)The joining of small molecules into macromolecules such as simple proteins and nucleic acids.3) The packaging of these molecules into “protobionts”, droplets with membranes that maintaining internal chemistry different to environment.4)The origin of self replicating molecules that made inheritance possible.

Question 34

what is endosymbiosis?

Answer 34

an evolutionary theory which explains the origin of eukaryotic cells from prokaryotes. It states that several key organelles of eukaryotes originated as symbiosis between separate single-celled organisms.1) mitochondria are the result of endocytosis of aerobic bacteria2) chloroplasts are the result of endocytosis of photosynthetic bacteria3) in both cases by large anaerobic bacteria who would not otherwise be able to exist in an aerobic environment.4) this arrangement became a mutually beneficial relationship for both cells (symbiotic).

Question 35

describe the evidence supporting the endosymbiotic theory

Answer 35

1) Chloroplasts and mitochondria have their own DNA (circular, no histones), distinct from that of the cell nucleus, and are inherited maternally 2) Ribosomes are present in chloroplasts and mitochondria. These are smaller than those in the cytoplasm of the cell, but the same size as those in bacteria3) Mitochondria are sensitive to the same antibiotics as bacteria eg chloramphenicol.4)Both are enclosed by a double membrane. The outer one from the host cell, the inner from the invader.5) Both reproduce by division, independently of nuclear division, like bacteria

Question 36

outline how evolving chloroplasts lost genes

Answer 36

1) Free-living cyanobacteria possess 3,000 genes, a chloroplast has only 100–200 genes2) When the prokaryote took up residence in the host, many genes, such as those coding for cell wall synthesis, were lost3) Sex among the hosts allowed them to share transferred genes; but the chloroplast genes now nuclear needed to express proteins in the chloroplast. To do this the gene was modified by adding a chloroplast-targeting sequence.

Question 37

what is Secondary Endosymbiosis?

Answer 37

a process in eukaryotic evolution in which a heterotrophic eukaryotic cell engulfed a photosynthetic eukaryotic cell which survived in a symbiotic relationship inside the heterotrophic cell

Question 38

what is a nucleomorph?

Answer 38

Nucleomorphs are small, vestigial eukaryotic nuclei found between the inner and outer pairs of membranes in certain plastids.

Question 39

describe the life cycle of Hatena

Answer 39

1) Hatena is a unicellular organism with a symbiotic unicellular alga inside. 2)The photosynthetic symbiont cell retains its nucleus, mitochondria(on), plastid, and occasionally a vestigial Golgi body, but the flagella, cytoskeleton, and endomembrane system are lost. 3)When the host cell divides one daughter cell retains, the other loses the photosynthetic symbiont4) This means it has to capture a new one when it is in the heterotrophic phase.5) Hatena alternates between a host phase that harbours a green symbiont and a predator phase that acquires the symbiont

Question 40

list the different types of plastids

Answer 40

• All plastids are derived from proplastids which are present in the meristematic regions of the plant. 1) Leucoplasts: colourless, storage plastids, starch (amyloplasts) protein, or oil droplets. found in In storage organs seeds, tubers.2) Chloroplast: chlorophyll, photosynthetic system, well developed membranes, may contain starch. found In leaves and other green parts of plant3) lipid soluble yellow, red or orange pigments (carotenoids) found in fruits and flowers. -All contain DNA, ribosomes etc.

Question 41

describe the development of plastids from a proplastid

Answer 41

1) Proplastid with double membrane2) Formation of vesicles from ingrowths of the inner membrane 3) Vesicles lining up in rows4) Coalescence of vesicles to form granal stacks5)Mature chloroplast 6) Chromoplast formed directly from a proplastid or by reversible redifferentiation of an amyloplast or Chloroplast7) Amyloplast formed directly from a proplastid

Question 42

outline the function of vacuoles

Answer 42

1) Provide turgor to drive cell growth.2) Storage:Secondary compounds giving flavours and antifeedants , Pigments, Protein,Tannins,Sugar and inulin (in onions) Crystals of silica or oxalate3) Accumulation. This process uses energy in the form of ATP.4)The vacuolar membrane (tonoplast) selectively admits, or prevents passage of materials into and out of the vacuole. 5)Vacuole enlargement drives plant cell growth

Question 43

describe the function of the cell wall

Answer 43

1) Distinguishes plant cells from animal cells2) Forms an exoskeleton for individual cells3) Is an active part of living cells4) Has high compression and bending strength and provides structural support for the plant5) Maintains cell shape6) Protects the protoplast from the outside world7) Consists of cross-linked macromolecules

Question 44

outline the composition and structure of the cell wall

Answer 44

1) Pectins – polysaccharides with Ca2+ and Mg2+ 2) Cellulose 3) Hemicellulose4) Lignin5) Part of a cellulose chain made up of thousands of β-1,4-linked glucose units6) The cellulose molecules are laid down parallel to one another and are held together by hydrogen bonds7) Cellulose chains are grouped into parallel bundles called microfibrils (~5 nm diameter

Question 45

what is Hemicellulose?

Answer 45

Hemicellulose is a polysaccharide with a branched structure made up of 5-carbon sugars: xylose, arabinose, mannose and other units as well as some glucose. It is not structured

Question 46

what is lignin and how is it formed?

Answer 46

1) Comprises 30% of the wood cell wall2) Responsible for the compressive strength of wood – rigidity3) Forms a matrix around the cellulose microfibrils4) Waterproofs the wall so that water can be conducted through special conduits (vessels) for long distances.How its formed:1) Enzymes catalyse dimerisation and dehydration2)This starts a chain reaction leading to the formation of a large polymer 3) Gives the cell high compressional load strength.

Question 47

why do cells need to communicate and respond to their environment?

Answer 47

1) in order to survive, and when appropriate replicate, it is critical that a cell is able to respond or adapt to changing environmental conditions - signals received may originate from other cells or from changes in physical environment and can take various forms. most cell communication involve the changing of chemical signals

Question 48

describe how prokaryotic cells respond to their environment.

Answer 48

1) prokaryotes respond primarily to environmental changes .2) bacteria respond to changing temperatures, osmotic stress, nutrients, pH etc by:- moving towards or away from the stimulus ( control of flagella motion) - the synthesis of new proteins to optimise survival under the prevailing conditions. ( activation of gene expression resulting in the synthesis of enzymes to use new sugar source)

Question 49

describe how unicellular talk to each other about sex

Answer 49

1) yeast cells use the exchange of chemical signals to find and attract suitable mating partners.2) the mating factors bind to receptors inducing changes in the cells that lead to their fusion. 3) the new cell combines in its nucleus all the genes from the two cells.- mating factors are short peptides if about 12 amino acids in length

Question 50

outline how multicellular organisms respond to their environment.

Answer 50

1) Respond to both their physical environment and to the presence of other cells. Cells in a multicellular organism need to “know” that they are in the correct place.2) Types of stimuli include: growth factors, cell-matrix contact, hormones, light (photons), cell-cell contact, odorants, touch, temperature 3) The responses are more complex and diverse and control both the behaviour of individual cells and the co-ordination of cellular responses in tissues.

Question 51

What is signal transduction?

Answer 51

The mechanisms by which a cell is able to respond, or adapt, to changes in its environment.

Question 52

why do we study signal transduction?

Answer 52

1) To understand how cells work. - circuit diagram of a cell.2) To better understand and treat disease.- many diseases are due to failure of signalling pathways, e.g.cancer

Question 53

where has our current understanding of cell signalling come from?

Answer 53

1) studying diverse species.-Yeast- Caenorhabditis elegans (nematode worm)- Drosophila genetics (fruit fly)- Rodent cell culture models and mouse genetics- Human cell culture models

Question 54

outline how external signals are received by the cell ?

Answer 54

communicating cells can be close together or far apart.1) cell junction communication - both animals and plants have cell junctions that allow molecules to pass readily between adjacent cells without crossing plasma membranes. Gap junctions between animal cells and plasmodesmata between plant cells.( exchange of ions and small molecules only)2) cell-cell recognition- two cells in an animal may communicate by interaction between molecules protruding from their surfaces 3) paracrine signalling- local regulators, such as growth factors are produced and secreted by the transmitting cell and then diffuse locally until they encounter target cells with appropriate receptors.4) synaptic signalling- a specialised form of paracrine signalling occurring at the synapse structure between two cells. More directed than general paracrine signals 5) Long distance ( endocrine or hormonal) signalling- the hormone is made in one part of the body and then transported via the blood stream to the target cell.- Cells receive/recognise external stimuli and convert (transduce) that recognition event into a response within the cell. The response is usually a change in one or more cellular activities.The series of steps that make up this process are called a signal transduction pathway.

Question 55

name the three phases of cell signalling

Answer 55

1) reception ( or recognition)2) transduction 3) response

Question 56

explain what happens during the reception phase of cell signalling

Answer 56

1) Reception is the target cell’s detection of a signal coming from outside the cell. A chemical signal is “detected” when it binds to a cellular protein usually at the cell surface.2) Ligands – External signal, agonist, stimuli or first messenger.e.g Proteins, peptides, lipids, small molecule. these bind to receptors switching them on3) Receptors – Specific cellular proteins (usually membrane spanning proteins at cell surface) which bind ligands- common families of cell surface receptors: Ion channel-linked receptors, G-protein-linked receptors,Enzyme-linked receptors (often protein kinases).

Question 57

explain what happens during the transduction phase of cell signalling

Answer 57

1) The transduction step(s) converts one type of signal (e.g. the initial stimulus or ligand binding) into another signal (e.g. an internal or 2nd messenger) and may also amplify the signal in the process.-Second messengers – Small chemical messengers that carry signalling information by diffusion from one part of a cell to another e.g.cyclic nucleotides (cAMP), calcium, nitric oxide.2) the receptor may recruit an effector to propagate the signal further into the cell. -Effectors – Enzymes that transduce ligand-activated signals into the cell. May catalyse the formation of second messenger molecules.-Adaptors – Proteins lacking enzyme activity that mediate physical interactions between proteins.3) Signal transduction pathways can be thought of as a series of switches. when the ligand binds with its receptor it switches the receptor on

Question 58

outline the signalling pathway of protein-tyrosine kinase receptor – Ras

Answer 58

1) Ligand (First messenger outside cell) binds to cell surface receptor 2) Effector enzyme(s) 2nd messenger( inside cell), Adaptors/Amplifiers3) Target (response) protein(s)Ras:- A common growth factor activated signalling pathway- Regulates changes of gene expression and cell cycle.- Activation of this pathway is linked to many cancers!

Question 59

summarise the events that occur in cell signalling

Answer 59

1)Specific molecular recognition events:-Between ligands and receptors.-Between adaptors and other transducers.2) Molecular switches:- G proteins.-Phosphorylation by kinases- dephosphorylation by phosphatases.3) Signal amplification between reception and response.

Question 60

what is the significance of molecular recognition during cell signalling ?

Answer 60

1) The ligand–receptor interaction determines the specificity of signalling.2) Like enzyme-substrate interactions, a ligand fits its receptor like a key in a lock. (Induced fit)

Question 61

define: agonist

Answer 61

a substance which initiates a physiological response when combined with a receptor.

Question 62

what is amplification?

Answer 62

1) when the Ligand-receptor interaction at the cell surface is converted into lots of activity (e.g. 2nd messengers) inside the cell. - Amplification of a signal by opening of an ion channel. the ligand binds, opens the channel and ions flow into the cell. change in ion concentration triggers cellular response. the ligand then dissociates and the channel closes -Amplification by enzymatic generation of a 2nd messenger. the first messenger outside the cell e.g. adrenaline binds to its receptor which switches on a G-protein that activates adenylyl cyclase (enzyme protein which converts ATP to cyclic AMP - second messenger). many molecules of cAMP are made for each enzyme molecule activated. The cAMP activate kinase enzymes which cause a cascade of reactions inside the cell. many molecules of cAMP will activate many target molecules amplifying the signal. Thus, one signaling molecule can cause many responses or a single receptor can cause many responses.

Question 63

explain what happens during the response stage of cell signalling

Answer 63

1) third phase of cell signalling, the transduced signal finally triggers a specific cellular response.2) Target (response) proteins- These are the signalling components at the end of a signalling pathway that bring about a change in cell activity contributing to the overall response. e.g. Activation/inhibition of metabolic enzymes,rearrangement of cytoskeleton, activation of specific genes in the nucleus, activation of a transcription factor leading to a change in gene expression.

Question 64

describe how a cell decided to survive or die?

Answer 64

1) Cells are constantly bombarded with signals from their surroundings and have to make sense of this.2) Different combinations of these signals lead to the cell undergoing different cell fates.3) Cell require signals continually from their surroundings to survive4) Death signals are mediated by specific extracellular ligands that bind to specific cell surface receptors and initiate intracellular signals.

Question 65

outline a key cell survival signalling pathway.

Answer 65

IGF1 -> IGF1R -> PI 3-kinase -> Protein kinase B (PKB/Akt) –> inactivates death proteins and promotes survival function

Question 66

what is apoptosis?

Answer 66

1) Highly controlled and organised process unlike other types of cell death (eg., necrosis).2) No new gene activity/protein synthesis required.3) Cells always ready to respond to death signals.

Question 67

explain how apoptosis occurs

Answer 67

1) cells damaged, stressed or triggered by body signals, begin apoptosis.2) the cell begins to shrink and form blebs. proteins are activated to break down cellular compartments3) enzymes break down the nucleus and the cell emits signals to attract macrophages 4) the cell breaks into several smaller pieces containing the cell components and destroyed nucleus 5) macrophages recognise the cell parts and remove them from the body.

Question 68

what is cell growth?

Answer 68

1) Involves an increase in cell size without and increase in cell number.2) Synthesis of new proteins, membrane lipids.3) Increase numbers of organelles.4) May involve replication of DNA but not necessary.5) growth is controlled by :growth factors, contact with adjacent cell, nutrient availability

Question 69

what is cell proliferation?

Answer 69

1) Involves replication of DNA and division to produce two cells2) usually follows on from a cell growth phase.3) If not a reductive division will occur resulting in one or more smaller cells.4) there are both positive and negative growth /proliferation signals

Question 70

name the different parts of the cell cycle

Answer 70

1) G1 – cell growth ( first growth phase)2) S – DNA synthesis3) G2 – gap 2: growth and preparation for mitosis 4) M - Mitosis ( prophase, metaphase, anaphase, telophase) - Checkpoints blocks the cell cycle and have to be removed to allow the cycle to proceed.-Signal transduction pathways when activated remove the blocks and allow cell cycle to proceed.

Question 71

what is Cell differentiation?

Answer 71

1) The process by which cells become specialised cell types2) Usually but not always involves them ceasing to proliferate.- stem cells can differentiate into any kind of cell; the type they become depends on environmental influences. These come from neighbouring cells, which are producing chemicals that influence the stem cell differentiation.- signals are detected through receptor molecules on the cell surface, and the activated genes direct the formation of the kinds of proteins the cell needs to specialise.

Question 72

How do signalling pathways control complex decisions?

Answer 72

1) a single receptor, many responses.2) Cell signalling and cell fate- an extracellular input, leads to an intracellular signal, this determines cell fate. growth, survival, differentiation, apoptosis 3) Different combinations of ouptuts will lead to different cell fates