Cellular Control

Question 1

Why is DNA degenerate?

Answer 1

-64 different triplets but only 20 different amino acids.
-Therefore each amino acid is coded for by more than one triplet.

Question 2

Substitution mutations

Answer 2

-One base replaced by another.

Question 3

Deletion mutation

Answer 3

-One or more bases removed.
-Causes a frameshift.

Question 4

Addition mutation

Answer 4

-One or more bases added.
-Results in a frameshift.

Question 5

Silent mutation

Answer 5

-When a base still codes for the same amino acid as the original base despite a mutation.
-Therefore the final polypeptide would remain the same.

Question 6

Non-sense mutation

Answer 6

-When a change in base leads to a premature stop codon being coded.
-This would lead to a premature end to the synthesis of the polypeptide (truncation).

Question 7

Mis-sense mutation

Answer 7

-When a change in base leads to a different amino acid being coded for.
-The polypeptide will have a single different amino acid that is different.

Question 8

E. Coli

Answer 8

-Bacterium.
-Capable of synthesising enzymes, such as those needed to metabolise lactose when lactose is present in the substrate.

Question 9

Beta-galactosidase

Answer 9

-Produced by E. Coli in presence of lactose.
-Catalyses hydrolysis of lactose into glucose and galactose.

Question 10

Lactose permease

Answer 10

-Produced by E. Coli in presence of lactose.
-Transports lactose into the cell.

Question 11

Structural gene (lac operon)

Answer 11

-Encodes proteins involved in the uptake and utilisation of lactose (beta-galactosidase and lactose permease).
-Made up of LacZ, LacY and LacA.

Question 12

Regulatory gene

Answer 12

-On the Lac operon.
-Encodes a repressor protein which controls when the structural gene is expressed.
-Two binding sites, on for lactose and one for LacO.

Question 13

RNA polymerase

Answer 13

-Binds to the promoter region to initiate transcription of the gene.

Question 14

LacZ

Answer 14

-In structural gene.
-Encodes beta-galactosidase.

Question 15

LacY

Answer 15

-In structural gene.
-Encodes permease proteins.

Question 16

LacA

Answer 16

-In structural gene.
-Encodes beta-galactosidase transacetylase, which adds an acetyl group to beta-galactosidase.

Question 17

Turning structural genes off

Answer 17

-When lactose is absent the repressor protein binds to lacO, meaning that RNA polymerase cannot bind to it and structural genes cannot be transcribed.

Question 18

Switching structural genes on

Answer 18

-When lactose is present it binds to the lactose binding site on the repressor protein.
-This changes the shape of the DNA binding site so that the protein now cannot bind to lacO.
-Therefore RNA polymerase can bind to the promoter region and structural genes can be transcribed.

Question 19

Transcriptional factors

Answer 19

-Proteins or short non-coding pieces of RNA.
-Move in from the cytoplasm and bind to DNA.
-Bind to the promotor region and aid or inhibit the attachment of RNA polymerase to DNA.
-Most in inactive form and activated by hormones or growth factors.

Question 20

Activators

Answer 20

-Type of transcriptional factor.
-Allows RNA polymerase to bind.
-Allows transcription to occur so gene is expressed.

Question 21

Repressors

Answer 21

-Inhibitor bound to TF’s.
-When a gene is not to be expressed the site of the TF that binds to DNA is blocked an inhibitor molecule.
-This then prevents transcription.
-They can also bind to the operator region itself and block RNA polymerase from binding.

Question 22

Splicesosome

Answer 22

-Consists of many snRNP’s.
-Causes the intron to form a loop shape.
-The intron is then excised and the exons spliced together.
-Mature mRNA is formed.
-Introns are destroyed or many become transcription factors.

Question 23

Harmful mutations

Answer 23

-70% of cystic fibrosis sufferers have a deletion of a triplet of base pairs in a haemoglobin beta protein.
-Protooncogenes can be changed into oncogenes by a point mutation, which promote uncontrolled cell division.
-Huntingdon disease is caused by a repeating section of CAG sequences.

Question 24

Alternative splicing

Answer 24

-Where exons are removed as well as introns so different polypeptides can be produced from the same gene/pre-mRNA.

Question 25

Cyclic AMP

Answer 25

-Formed from adenyl cyclase hydrolysing ATP. -Activates the enzyme protein kinase A by binding to it, causing a change in the 3D structure.

Question 26

Protein kinase A

Answer 26

-Phosphorylates proteins (and hydrolyses ATP). -This activates enzymes in the cytoplasm, such as those that convert glucose to glycogen. -Can also phosphorylate CREB, which can enter the nucleus as a transcription factor to regulate transcription.

Question 27

LacO

Answer 27

-Operator region of lac operon. -LacI repressor protein binds to it in absence of lactose.

Question 28

Promoter region

Answer 28

-RNA polymerase binds to it in presence of lactose to begin transcription in lacZ and lacY. -Blocked by repressor protein.

Question 29

Receptors on cell membrane

Answer 29

-Binds to a signalling molecule eg a hormone. -Activates a transmembrane protein which activates a G protein.

Question 30

G protein

Answer 30

-Activated by a transmembrane protein. -Activates adenyl cyclase enzymes, which catalyse the formation of cAMP from ATP.

Question 31

Homeotic genes

Answer 31

-Involved in controlling anatomical development of an organism. -Many contain homeobox sequences. These are known as homeobox genes.

Question 32

Homeobox sequence

Answer 32

-180 DNA base pairs (no introns) encoding a 60 amino acid sequence called a homeodomain sequence within a protein (transcription factor in nucleus).

Question 33

Homeodomain sequence folding

Answer 33

-Folds into H-T-H shape, consisting of two helices and one turn. This recognises the TAAT sequence of the enhancer region of the gene that is to be transcribed. -This sequence binds to DNA regulating the transcription of genes.

Question 34

Discoveries of homeobox genes

Answer 34

-1984, a team headed by Walter J McGinnis found that the homeobox sequence in 1983 fruitflies also exists in mice, and that the base sequences were very similar. -1984, Edward de Robertis discovered Hox genes in an African clawed frog. These are only present in animals, while homeobox genes are found in animals, plants and fungi.

Question 35

Characteristics of Homeobox genes

Answer 35

-In animals, plants and fungi. -Very similar base sequences between organisms. -Arose before Paleozoic era (541 mya). -Have been conserved from an early ancestor.

Question 36

Hox genes (basic)

Answer 36

-Regulate the development of embryos along the anterior-posterior (head-tail) axis. -If genes are mutated then abnormalities can occur, such as legs instead of antennae. -Hox genes are arranged in clusters of up to 10 genes. In four limbed vertebrates there are four clusters. -Similar across different animals.

Question 37

Hox genes expression in embryos

Answer 37

-Expressed in order along the anterior-posterior axis on a developing embryo. -Sequential and temporal order of expressions corresponds to development of body parts. This is known as colinearity. -Hox genes encode homeodomain proteins that act in the nucleus as transcription factors and can activate other genes to promote cell division, apoptosis, cell migration and regulation.

Question 38

Regulation of hox genes

Answer 38

-Genes called gap genes and pair rule genes regulate hox genes. -This are regulated by maternally supplied mRNA from the egg cytoplasm.

Question 39

Mitosis with Homeobox genes

Answer 39

-Regulated using homeobox and hox genes, which ensure that the new daughter cells contains the full genome and is a clone of the parent cell. -During cell differentiation some of the genes are not expressed. -Leonard Hayflick (1962) showed that normal body cells divide around 50 times before dying.

Question 40

Apoptosis process

Answer 40

-Described in 1842 by Carl Vogt. Re-examined by John Foxton Ross-Kerr in 1965 and accepted in 1972. -Protease enzymes called caspases break down cytoskeleton. -Cytoplasm becomes dense with tightly packed organelles. -Cell surface membrane changes and protrusions called blebs form. -Chromatin condenses, the nuclear envelope breaks and DNA breaks into fragments. -The cell breaks into vesicles that are ingested by phagocytes.

Question 41

Nitric oxide

Answer 41

-In signalling molecules released by stimulated cells. -Induces apoptosis by making the inner mitochondrial membrane more permeable to hydrogen ions and dissipating the proton gradient. -Proteins are released into the cytoplasm where they bind to apoptosis inhibitor proteins and allow apoptosis to occur.

Question 42

Control of Apoptosis

Answer 42

-Cell signals used. -Released by cells when genes involved in regulating the cell cycle and apoptosis respond to stimuli internally and externally. -These include cytokines, hormones, growth factors and nitric oxide.

Question 43

Use of apoptosis

Answer 43

-Prevents proliferation of cell types without releasing hydrolytic enzymes. -Causes digits to separate during limb development. -Removes ineffective or harmful T-lymphocytes in the immune system. -The rate of cells dying should equal the rate of cells produced by mitosis. -In children (8 to 14) 20-30 billion cells per day apoptose. -In adults 50-70 million cells per day apoptose.

Question 44

Colinearity

Answer 44

-During embryo development the hox genes are expressed beginning from the anterior to the posterior. -This determines where and when they are expressed.

Question 45

Thalidomide

Answer 45

-Affected genes HoxA11 and HoxD11, involved in forearm development, which led to undeveloped forearms in children. -Now used to stop cancers as it prevents the formation of capillary networks.

Question 46

Internal stimuli of apoptosis

Answer 46

-Damage to DNA. -Release of hormones. -Psychocological stress. -Nitric oxide

Question 47

External stimuli of apoptosis

Answer 47

-Pathogen attack. -Lack of nutrients. -Change in conditions such as light intensity and temperature.