Chapter 19 - Cellular Control Flashcards

Question

Lac operon

Answer 1

structural genes in prokaryotes form an operon - lac operon controls the production of the enzyme lactase (also called β-galactosidase) + 2 other structural proteins - Lactase breaks down the substrate lactose so that it can be used as an energy source in the bacterial cell It is known as an inducible enzyme (only synthesised when lactose is present) - helps prevent the bacteria from wasting energy and materials

Answer 2

- A group or a cluster of genes that are under the control of the same regulatory mechanism + expressed at the same time

Answer 3

promoter for structural genes operator structural gene lacZ that codes for lactase structural gene lacY that codes for permease (allows lactose into the cell) structural gene lacA that codes for transacetylase

Answer 4

- B-galactosidase, lactose permease and transacetylase

Answer 5

- transcribed onto a long molecule of mRNA

Answer 6

- binding of RNA polymerase results in a slow rate of transcription that needed to be increased to produce the required quantity of enzymes to metabolise lactose efficiently - this is achieved by binding of cAMP receptor protein, which is only possible when CRP is bound to cAMP

Answer 7

- beneficial mutation - harmful mutation - neutral mutation

Answer 8

- has two binding sites that allow it to bind to the operator in the lac operon and also to lactose (the effector molecule) - When it binds to the operator it prevents the transcription of the structural genes as RNA polymerase cannot attach to the promoter - When it binds to lactose the shape of the repressor protein distorts and it can no longer bind to the operator

Answer 9

- regulatory gene is transcribed and translated to produce lac repressor protein - lac repressor protein binds to the operator region upstream of lacZ - due to the presence of the repressor protein, RNA polymerase is unable to bind to the promoter region - transcription of the structural genes does not take place - No lactase enzyme is synthesised

Answer 10

- uptake of lactose by the bacterium - lactose binds to the second binding site on the repressor protein, distorting its shape so that it cannot bind to the operator site - RNA polymerase is then able to bind to the promoter region + transcription takes place - mRNA from all three structural genes is translated - lactase is produced and lactose can be broken down and used for energy by the bacterium

Answer 11

- effector molecule binds to a repressor protein produced by a regulatory gene. However this binding actually helps the repressor bind to the operator region and prevent transcription of the structural gene - opposite of the lac operon: when there is less of the effector molecule, the repressor protein cannot bind to the operator region and transcription of the structural genes goes ahead, meaning the enzyme is produced.

Answer 12

Eukaryotes can use transcription factors to control gene expression via RNA poly proteins that bind to specific regions of DNA to control the transcription of genes

Answer 13

Some transcription factors bind to the promoter region of a gene - bind either allows or prevents transcription of gene from taking place - presence of a transcription factor will either increase or decrease the rate of transcription of a gene

Answer 14

- lipid-soluble molecule + therefore diffuses through the plasma membrane of cells - moves to the nucleus + binds to an oestrogen receptor - these receptors are actually transcription factors that are able to initiate transcription for many different genes by binding to their promoter regions - Once bound, oestrogen causes a change in the shape of the receptor - As a result, the receptor moves away from the protein complex it is normally attached to + binds to the promoter region of one of its target genes - this allows RNA polymerase to bind and to begin transcribing that gene

Answer 15

- Gibberellin is a hormone found in plants (e.g. wheat and barley) that controls seed germination by stimulating the synthesis of the enzyme amylase - does this by influencing transcription of the amylase gene - When gibberellin is applied to a germinating seed there is an increased amount of the mRNA for amylase present

Answer 16

The breakdown of DELLA protein by gibberellin is necessary for the synthesis of amylase components involved: Repressor protein DELLA, Transcription factor PIF DELLA protein is bound to PIF, preventing it from binding to the promoter of the amylase gene so no transcription can occur Gibberellin binds to a gibberellin receptor and enzyme which starts the breakdown of DELLA PIF is no longer bound to DELLA protein and so it binds to the promoter of the amylase gene Transcription of amylase gene begins Amylase is produced

Answer 17

- coding sequences are called exons + these are the sequences that will eventually be translated into the amino acids that will form the final polypeptide - non-coding sequences are called introns and are not translated (they do not code for any amino acids) - When transcription of a gene occurs, both the exons and introns are transcribed

Answer 18

As the introns are not to be translated, they must be removed from the pre-mRNA molecule - exons are then all fused together to form a continuous mRNA molecule called mature mRNA that is ready to be translated (splicing) - Splicing ensures that only the coding sections of mRNA are used to form proteins by translation (if any introns were included in the mature mRNA, the resulting protein would not be formed properly and may not function as it should)

Answer 19

After polypeptides are formed by translation, they undergo modifications in the Golgi apparatus or in the cytosol Some polypeptides may then require activation by cyclic AMP (cAMP) cAMP is derived from ATP and is formed by the action of the enzyme adenyl cyclase

Answer 20

- the sequence of homeobox genes - homeodomain is sequenced, transcribed and translated to form a protein called Helix - turn - helix protein that fits with DNA

Answer 21

- it is alpha helix with normal shape and then it turns and then back to normal shape

Answer 22

- forms a homeodomain sequence that regulates transcription - responsible for the genetic control of the development of limbs and organs in different organisms at correct time and location - they help to form the basic pattern of the body eg. control polarity of organism (which end is tail or head) segmentation of organisms (insects have segments in their main body) - seen as 'master genes' that control which genes function at different stages of development - maintained by natural selection and won't change - e.g no use of tail so gene turned off and tail won't grow in womb

Answer 23

subset of homeobox genes but only in animals - determine body plans of anterior-posterior (head to tail) - Vertebrates have four Hox clusters (each containing 9-11 Hox genes), which are found on different chromosomes - linear order to the Hox genes in each Hox cluster + this order is directly related to the order of the regions of the body that they affect

Answer 24

- the field of study involving hox genes and body plans from an embryo to full adult

Answer 25

Group of hox genes

Answer 26

- the hox genes of a fruit fly was mapped and colour coded - different hox genes of diff parts of fruit fly was turned on and off to see what happens - e.g legs out the head etc - advantages - not much ethical problems of using fruit fly, cheap, they make lots of offspring

Answer 27

mRNA in cytoplasm of egg made from 'gap genes'. They reulate the homeobox genes.

Answer 28

- initially used for insomnia back then - doctors used it on pregnant insomniacs and realised it stops morning sickness - kept prescribing - caused limb abnormalities due to prevention of normal expression of hox genes in fetus - inhibits some homeobox genes

Answer 29

- also a transcription factor - similar to thalidomide - should be avoiding during pregnancy and told to avoid foods with it

Answer 30

Mitosis is controlled by various different genes that are categorised into two distinct groups: Proto-oncogenes are genes that stimulate cell division Tumour-suppressor genes are genes that reduce cell division Tumour-suppressor genes can also stimulate apoptosis in cells with damaged DNA that cannot be repaired This protects the body as it ensures that any cells that are genetically damaged (and that could, therefore, lead to cancer) are destroyed

Answer 31

- enzyms break down cytoskeleton - cytoplasm becomes dense with organelles tightly packed

Answer 32

- cell surface membrane changes and small bits called blebs form - Chromatin condenses - Nuclear membrane breaks and the DNA breaks up into fragments

Answer 33

- Cell breaks up into vesicles - Vesicles taken up by phagocytosis (phagocytes) - Cellular debris are disposed of and does not damage any cells or tissues

Answer 34

- Apoptosis is important in development as, in some cases, some cells that are produced (by mitosis) earlier on in development may no longer be needed - so these cells are destroyed (by apoptosis) as part of the development of the organism

Answer 35

cyclins and cyclin-dependent kinases (CDKs) -> cyclins act as regulators -> CDKs act as catalysts (once activated by cyclins) eg. CDKs that have been activated by cyclins will catalyse the phosphorylation of particular target proteins, which can either activate or inactivate them - ensures the cell cycle progresses from one stage to the next -diff cyclins are produced at different stages of the cell cycle in response to internal molecular signals

Answer 36

Internal cell stimuli (e.g pH, enzymes) External cell stimuli (e.g light, temp)

Answer 37

Internal factors that affect apoptosis and the cell cycle include: Irreparable genetic damage RNA decay Internal biochemical changes that lead to cell changes or cellular injury (e.g. oxidative reactions) Production of cyclin D These factors can all initiate apoptosis in cells that are undergoing cell stress

Answer 38

External factors that affect apoptosis and the cell cycle include: - presence of cell signalling molecules like cytokines from the immune system, hormones + growth factors - viruses + bacteria, harmful pollutants or ultraviolet light can affect the delicate balance of mitosis and apoptosis by damaging or destroying cells faster than they can be repaired or replaced Cells often respond to such stressful stimuli by activating pathways to increase their chance of survival, or by initiating apoptosis eg. a cell will often begin by defending itself and trying to recover from the stressful stimulus by counteracting any damage caused to it but, if the stressful stimuli remain, cell death pathways are activated (i.e. apoptosis is initiated)

Chapter 19 - Cellular Control Flashcards

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