cellular control

Question 1

what is a mutation?

Answer 1

a mutation is a change in the sequence of bases in DNA

Question 2

what are the three types of mutation?

Answer 2

• substitution
• insertion
• deletion

Question 3

describe substitution

Answer 3

the substitution of a single nucleotide changes the codon that it occurs in. if it codes for a new amino acid this leads to a change in the primary structure of a protein, and potentially a new protein synthesised. as the genetic code is degenerate the new codon may still lead to the same amino acid being produced and same protein synthesised

Question 4

describe insertion

Answer 4

insertion leads to a frame shift mutation because bases are read in groups of three consecutively. insertion changes the reading frame of bases changing every successive codon from then on

Question 5

describe deletion

Answer 5

deletion leads to a frame shift mutation as bases are read in groups of three consecutively. deletion changes the reading frame of bases changing every successive codon from then on

Question 6

what can the effects of mutations be ?

Answer 6

• beneficial
• neutral
• harmful

Question 7

describe a neutral mutation

Answer 7

there is no effect, positive or negative, and a normally functioning protein is still synthesised

Question 8

describe a damaging mutation

Answer 8

the phenotype is effected negatively as the proteins that are synthesised are non functional or not synthesised at all. this can interfere with essential processes

Question 9

describe a beneficial mutation

Answer 9

very rare but this is when a useful characteristic in the phenotype is produced

Question 10

what’s an example of a beneficial mutation?

Answer 10

a mutation in the cell surface membrane which means that HIV cannot enter cells making someone immune to HIV

Question 11

what are mutagens ?

Answer 11

chemical physical or biological agents which cause mutations

Question 12

what are some examples of mutagens?

Answer 12

• ionising radiation such as x-rays which break DNA strands
• viruses as viral DNA may insert itself into a genome changing the base sequence

Question 13

what are nonsense mutations?

Answer 13

when a codon becomes a stop codon instead of coding for an amino acid. this results in a shorter non functional protein being synthesised

Question 14

what are missense mutations?

Answer 14

the incorporation of an incorrect amino acid into the primary structure when the protein is synthesised

Question 15

what are point mutations?

Answer 15

mutations where only one nucleotide is synthesised

Question 16

what are chromosome mutations?

Answer 16

mutations that affect the whole chromosome, they usually occur in meiosis

Question 17

what are the three types of chromosome mutation?

Answer 17

• deletion
• translocation
• inversion

Question 18

describe translocation mutations in chromosomes

Answer 18

a section of one chromosome breaks off and joins another non homologous chromosome

Question 19

describe inversion in chromosome mutations

Answer 19

a section of chromosome breaks off, is reversed and then joins back onto the chromosome

Question 20

what is gene regulation?

Answer 20

gene regulation is required for cells to work in a coordinated way and respond to changes in the internal and external environment.

Question 21

how are genes regulated?

Answer 21

• transcriptional (genes turned on/off)
• post transcriptional (mRNA can be modified which regulates translation and the types of protein produced)
• translational (translation can be stopped/started)
• post translational (proteins can be modified after synthesis which changes their functions)

Question 22

what are the forms of transcriptional control ?

Answer 22

• chromatin remodelling
• histone modification
• lac operon

Question 23

describe chromatin remodelling

Answer 23

DNA is a very long molecule so it is tightly wrapped around histones allowing it to be packed into a cell. this DNA protein complex is called chromatin
heterochromatin is tightly wound DNA, the transcription of genes is not possible as RNA polymerase cannot access the genes.
euchromatin is loosely wound DNA which is freely transcribed

Question 24

describe histone modification

Answer 24

DNA coils around histones because they are positively charged and DNA is negatively charged. histones can be modified to increase/decrease the degree of packing.
acetylation (adding acetyl groups and phosphorylation reduces the positive charge causing DNA to coil less tightly allowing certain genes to be transcribed
methylation makes the histones more hydrophobic so DNA coils more tightly preventing transcription

Question 25

what is epigenetics ?

Answer 25

the control of gene expression by the modification of DNA

Question 26

what is an operon?

Answer 26

a group of genes that are under control by the same regulatory mechanism and expressed at the same time

Question 27

why are operons more likely found in prokaryotes?

Answer 27

their small size and simple structure genomes

Question 28

describe the lac operon

Answer 28

a group of three genes involved in the metabolism of lactose. glucose is easier to metabolise but if it’s in short supply lactose can be used as a respiratory substrate. lacI, a regulatory gene is located near the operon and codes for a repressor protein which prevents the transcription of the structural genes in the abscence of lactose. the repressor protein is constantly produced and binds to an operator which prevents RNA polymerase binding to DNA and beginning transcription (down regulation). when lactose is present it binds to the repressor protein so it cannot bind to the operator allowing RNA polymerase to bind to the promoter and the three structural genes are transcribed and the enzymes synthesised

Question 29

what is the role of cAMP in the lac operon?

Answer 29

the bonding of RNA polymerase still only results in slow transcription that needs to be up regulated to produce the tequired quantity of enzymes to metabolise lactose. cAMP comes in to up regulate this when CRP binds to it. when glucose is present, the levels of cAMP decrease reducing transcription of the genes that cause the metabolism of lactose

Question 30

what are the methods of post transcriptional controll ?

Answer 30

• RNA processing • RNA editing

Question 31

describe RNA editing

Answer 31

the nucleotide sequence of some mRNA molecules can be changed through addition, deletion or substitution increasing the range of proteins that can be produced from a single mRNA molecule or gene

Question 32

describe RNA processing

Answer 32

the product of transcription is pre-rna. pre-rna is modified using mature rna before it can bind to a ribosome and synthesise a protein. a cap (modified nucleotide) is added onto the 5’ end and a tail (chain of adenine nucleotides) is added onto the 3’ end. these help stabilise dna and delay degrading the cytoplasm. the cap aids the binding of mRNA to ribosome

Question 33

when does splicing occur?

Answer 33

when RNA is cut and the introns are removed and the exons are joined together. they both occur in the nucleus.

Question 34

describe protein kinases as a form of translocational control

Answer 34

protein kinases are enzymes that catalyse the addition of phosphate groups to proteins. phosphate groups change the tertiary structure and therefore the function. many enzymes are activated by phosphorylation. kinases are activated by messenger cAMP

Question 35

what are the methods of post translational control?

Answer 35

• addition of non protein groups • modifying amino acids and the formation of bonds such as disulphide bridges • folding or shortening of proteins • modification by cAMP

Question 36

what are homeobox genes?

Answer 36

genes involved in regulating gene expression. homeobox genes are regulator genes which bind to dna and switch genes on/off. because of this they are highly conserved in plants animals and fungi. they are a section of DNA 180 base pairs long coding for a protein 60 amino acids long

Question 37

what are hox genes?

Answer 37

one group of homeobox genes that are only present in animals. they are responsible for the correct positioning of body parts. there are 39 hoc genes in humans

Question 38

what are diploblastic animals?

Answer 38

animals that have two primary tissue layers

Question 39

what are tripoblastic animals?

Answer 39

animals which have three primary tissue layers

Question 40

what is radial symmetry ?

Answer 40

seen in dipoblastic animals like jellyfish, radial symmetry is when animals only have a top/bottom

Question 41

what is bilateral symmetry?

Answer 41

seen in most animals and is when organisms have both left and right sides and a head/tail.

Question 42

what is the role of mitosis

Answer 42

to increase the number of cells leading to growth

Question 43

what is apoptosis?

Answer 43

programmed cell death. apoptosis kills cells to shape the body by removing unwanted cells/tissues. they release chemical signals which stimulate mitosis and cell proliferation leading to the remodelling of tissues

Question 44

describe the process of apoptosis

Answer 44

the nucleus condenses causing the cell to shrink and bleb, before being removed by exocytosis

Question 45

what can the expression of regulatory genes be influenced by?

Answer 45

the environment, both internally and externally