cellular control

Question 1

why is that all organisms carry the same genes but the structure and function of different cells varies ?

Answer 1

• this is because not all genes are expressed(transcribed and used to make functional protein)- they are selectively switched on or off . because cells show different gene expression , different proteins are made and modify the cell - they determine the cell structure and control the cell process.

Question 2

what are the different levels gene expression can be controlled at ?

Answer 2

transcriptional, post transcriptional and post translational level.

Question 3

how can gene expression be controlled at transcriptional level ?

Answer 3

by altering the rate of transcription of genes. eg increased transcription produces more mrna , which can be used to make more protein.

Question 4

how is transcriptional level altering the rate of transcription of genes controlled ?

Answer 4

its controlled by transcription factors - they are protein that bind to dna and switch genes on or off by increasing or decreasing the rate of transcription.

Question 5

whats an activator?

Answer 5

factors that increase the rate of transcription

Question 6

whats an repressor ?

Answer 6

factors that decrease the rate of transcription.

Question 7

what does the shape of a transcription factor determine and what does that mean?

Answer 7

shape of a transcription factor determines weather it can bind to dna or not and it can sometimes be altered by binding of other mollecules such as hormones this means that the amount of certain molecules in an certain enviorment or cell can control the synthesis os some protein by affecting transcription factor binding.

Question 8

transcription factors - what happenes in eukaryotes

Answer 8

transcription factors bind to specific dna sites near the start of the target genes-the genes they control the expression of.

Question 9

transcription factors - what happens in prokaryokes

Answer 9

the control of the gene expression often incoves transcription factors binding to operons.

Question 10

what’s an operon?

Answer 10

An operon is a section of a DNA that contains a cluster of structural genes , that are transcribed together as well as control elements and sometimes a regulatory gene.

Question 11

whats a structural gene ?

Answer 11

its a gene that codes for a useful proteins such as enzymes

Question 12

what are the control elements? - define promotor and operator

Answer 12

a control element include promoter ( a dna sequence located before the structural genes that rna polymerase binds to ) and an operator (a dna sequence that the transcription factors bind to)

Question 13

whats a regulatory gene?

Answer 13

its a gene that codes for an activator and a repressor

Question 14

give an example of an operon?

Answer 14

• Ecoli is a bacterium that respires glucose, but it can use lactose if glucose isn’t available.
• the genes that produce the enzymes needed to respire lactose are found on an operon called a lac operon.
• the lac operon has three structural genes – lacZ , lacy and lacA , which produce proteins that help bacteria digest lactose.

lactose not present

• then the regulatory gene (lacl) produces a lac repressor which is a transcription factor that binds to the operator site when theres no lactose present. this blocks transcription because RNA polymerase cant bind to the promoter.

lactose is present

• it binds to the repressor changing the repressors shape so that it can no longer bind to the operators site
• Rna polymerase can now begin transcription of structural genes.

Question 15

where is mrna edited ?

Answer 15

at post transcriptional level

Question 16

how is mrna edited at post transcriptional level?

Answer 16

• genes in eukaryotic DNA contain sections that don’t code for amino acids.
• these sections of DNA are called introns. All the bits that do code for amino acids are called exons.
• during the transcription the introns and exons are both copied into mrna. mrna strands containing intons and exons are called primary mrna transcript.
• introns are removed from the primary mRNa strands by a process called splicing-introns are removed and exons joined ,forming mature mRNA strands. this takes place in the nucleus.
• the mature mRNA then leaves the nucleus for the next stage of protein synthesis(translation).

Question 17

when some proteins are not activated to be synthesised what happenes?

Answer 17

• then camp activates some proteins.
• protein activation is controlled by molecules such as hormones some of the molecules work by binding to cell membrane and triggering the production of cyclic AMP inside the cell.
• Camp then activates proteins inside the cell by altering their three dimensional structure.
• for eg : altering the 3d structure can change the active site of an enzyme.

Question 18

how does camp activate protein kinase a (PKA)

Answer 18

• PKA is an enzyme made of four subunits.
• when camp isn’t bound the four units are bound together and are inactive.
• when camp binds, it causes a change in the enzyme’s 3d structure , releasing the active subunits - PKA is now active.

Question 19

whats a mutation

Answer 19

mutations are changes to the base sequence of DNA

Question 20

what are the types of mutations :

Answer 20

• substitution
• insertion
• deletion

Question 21

subsitution

Answer 21

its when one or more bases are swapped for another eg: ATGCCT becomes ATTCCT

Question 22

DELETION

Answer 22

its when one or more bases are removed eg: ATGCCT BECOMES ATCT

Question 23

INSERTION

Answer 23

one or more babes are added eg ATGCCT TO ATGACCT

Question 24

what effect can a mutation have

Answer 24

• neutral
• beneficial
• harmful

Question 25

what does having aneutral effect on a proteins function mean

Answer 25

• neutral affect on protein function wont affect the organism overall.
• the mutation change a base in a triplet, but the amino acid that the triplet codes for doesn’t change. this happens because some amino acids are coded by more than one triplet. EG: TAT and TAC code for tyrosine , so if TAT is changed to TAC the amino acid wont change.
• the mutation produces a triplet that codes for different amino acids but the amino acid is chemicaly similar to the original so its functions are like the original amino acid.
• however some mutations may change proteins structure and make it less active.

Question 26

what are the mutations with beneficial effect

Answer 26

• they increase its chance of survivaleg some bacterial enzymes breakdown certain antibodies. mutations in the genes that code for these enzyes could make them work on a wider range of antibiotics. this is a beneficial to bacteria because antibiotic resistance can help them to survive.

Question 27

what are the mutations with harmful effects

Answer 27

decreases its chance of survival
eg cystic fibross can be caused by deletion of three babes in the gene that codes for CFTR (ystic fibrosis transmembrane condunctane regulator) protein. the mutated CFTR protein folds incorrectly sp its broken down . this leads to excess mucus production, which affects the lungs of cf sufferes.

Question 28

whats a body plan

Answer 28

its a general structre of an organism

Question 29

what controls the development of a body plan

Answer 29

proteins control the development of body plans - they help set up the basic body plan so that everything is in its right place : eg legs grow where they are meant to grow

Question 30

what’s an hox genes

Answer 30

its the proteins that control body plan development are coded by genes called hox genes , similar hox genes are found in huumans , animals ,plants , and fungi which means body plan is controlled in a similar way.

Question 31

whats an homeobox sequence

Answer 31

they are the hox genes regions - which are highly conserved - this means that these sequences have changed very little during the evolution of different organisms that possess these homeobox sequence.

Question 32

how do hox genes control development?

Answer 32

• hoxgenes code for a part of protein called the homeodomain.
• the homeodomain binds to specific sits on dna, enabling the protein to work as a transcriptional factor.
• the proteins bind to dna at the start of development genes, activating or repressing transcription and so altering the production of proteins involved in the development of the body plan.

Question 33

what are the two main feautures involved in development of a body plan?

Answer 33

• apoptosis

- mitosis

Question 34

how is apoptosis involved in the development of a body plan?

Answer 34

• some cells die and breakdown as a normal part of the development.
• this is highly controlled process called apoptosis / programmed cell death.

Question 35

how is the cell broken down once apoptosis is triggered ?

Answer 35

1- enzymes inside the cell break down important cell components such as proteins in the cytoplasm amd dna in the nucleus..
2-as the cells content are broken down it begins to shrink and breaks up into fragments.
3-the cell fragments are engulfed by phagocytes and digested.

Question 36

how is mitosis involved in the development of a body plan ?

Answer 36

mitosis and differentiation create the bulk of body parts and then apoptosis refines the parts by removing the unwanted structures.
-during development, genes that control apoptosis and genes that control mitosis are switched on and off in appropriate cells. this means that some cells die, whilst some new cells are produced and correct plant develops.

Question 37

how can genes that regulate apoptosis and the cell cycle can respond to stimuli ? - internal and external - give examples

Answer 37

• an internal stimulus could be a dna damage. if the dna damage is detected during cell cycle, this can result in the expression genes which cause the cycle to be paused and can even trigger apoptosis.
• an external stimulus, such as stress caused by a lack of nutrient avalibility, could result in a gene expression that prevents cells from undergoing mitosis. gene expression which leads to apoptosis being triggered can also be caused by an external stimulus such as attack by a pathogen.