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Biology > Module 6- Cellular control > Flashcards

Module 6- Cellular control Flashcards

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AP® Biology flashcards Biology 101 flashcards
1
Q

Definition of a mutation

A

Changes in the base sequence of DNA

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2
Q

What can mutations be caused by?

A

Insertion, deletion, substitution

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3
Q

Are mutations often more harmful or beneficial?

A

Harmful because they interrupt the normal functioning of a protein

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4
Q

Definition of a point mutation

A

When only 1 nucleotide is affected as 1 base is substituted

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5
Q

What will happen if the new codon codes for a different amino acid?

A

A change in the primary structure of the protein will occur

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6
Q

What does degenerate mean?

A

The new codon may still code for the same amino acid leading to no change in the protein synthesised

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7
Q

What is a frame shift?

A

When the reading frame of the sequence of bases shifts due to an insertion or a deletion. This will change every successive codon from the point of mutation due to the DNA being non overlapping. The same effect is seen no matter how many bases are added or deleted unless it is a multiple of 3 where the reading frame will not be shifted but the protein formed will still be affected as a new amino acid is added/ deleted

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8
Q

What does non overlapping mean?

A

Each base is read only once and adjacent codons don’t overlap

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9
Q

What are the 3 point mutations and explain them?

A

-silent mutations-if 1 base is substituted and the triplet codon changes but still codes for the same amino acid

-nonsense mutation-if the point mutation results in the generation of a stop codon. It will generated a truncated protein that will not be able to carry out its function

-missense mutation-if the change in base sequence leads to a change in amino acid sequence. This changes the primary structure, therefore the secondary and tertiary structure may also change

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10
Q

Effects on mutations

A

no effect- no effect on the phenotype of the organism because normally functioning proteins are still synthesised.e.g whether your earlobe is attached or not has no advantage/disadvantage

negative effects- the phenotype of an organism is effected negatively because proteins are no longer synthesised or are not functional. This can interfere with an essential process e.g sickle cell anaemia results in red blood cells being sickle shape and aren’t as efficient at transporting oxygen around the body.

positive effects-very rarely is a protein synthesised that has a beneficial characteristic in the phenotype e.g mutation in the lactose gene allows adults to digest lactose

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11
Q

What is a mutagen?

A

chemical, physical or biological agent which causes mutations

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12
Q

What is a chemical mutagen?

A

deaminating agent chemically alter bases in DNA such as converting cytosine to uracil in DNA changing the base sequence

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13
Q

What is a physical mutagen?

A

ionising radiation such as X rays break one or both of the DNA strands. Some breaks can be repaired but mutations can occur in the process

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14
Q

What is a biological mutagen?

A

-alkylating agents-methyl or ethyl groups are attached to bases resulting in the incorrect pairing of bases during replication
-base analogs-incorporated into DNA in place of the usual base during replication, changing the base sequence
-viruses-viral DNA may insert itself into a genome, changing the base sequence

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15
Q

What is a somatic mutation

A

mutation during mitosis
it is not passed onto offspring as occurs within a body cell

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16
Q

What are the 4 chromosome mutations and explain them?

A

Deletion-a section of chromosomes breaks off and is lost within the cell

Duplication-sections get duplicated on a chromosome

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

Inversion- a section of chromosome breaks off, is reveresed and then joins back onto the chromosome

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17
Q

What are chromosome mutations?

A

-can arise spontaneously during meiosis
-these will be passed onto offspring as occurs within a gamete cell
-will affect the whole chromosome or number of chromosomes

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18
Q

What are the 2 types of genes in gene regulation and what do each of these code for?

A

Housekeeping genes- enzymes which are necessary for a metabolic reaction for basic cellular function like respiration are constantly required so are synthesised at a relatively constant rate

Tissue specific genes- if an enzyme is required for a reaction that only happens at certain times and at varying rates are not constantly required

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19
Q

Are the stimuli that produce change in gene expression and responses more complex in prokaryotes or eukaryotes?

A

Eukaryotes because multicellular organisms not only have to respond to changes in the internal environment but also the external environment

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20
Q

Why do we need gene regulation?

A

so cells are able to specialise and work in a coordinated way. Also to prevent vital resources from being wasted

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21
Q

What are the 3 levels of gene regulation and briefly explain them

A

Transcriptional-genes can be turned on/off

Post transcriptional- mRNA can be modified which regulates translation and the types of protein produced

Post translational-proteins can be modified after synthesis which changes their functions

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22
Q

Are operons more common in prokaryotes or eukaryotes?

A

Prokaryotes due to their smaller and simpler structure of genomes

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23
Q

Explain operons and their functions

A

-Bacterial genes are often organised into common pathways called operons for more coordinated regulation of expression
-An operon is a group of genes that function as a single transcription unit and are controlled by the same promoter
-The operon includes a regulatory gene that codes for a receptor protein which binds to the operator in turn preventing RNA polymerase transcribing the gene of interest

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24
Q

What are the 3 types of regulatory molecules that affect the expression of operons in prokaryotes?

A

Repressors- proteins that suppress transcription of a gene in a response to an external stimulus

Activators- proteins which increase transcription of a gene in response to an external stimulus

Inducers- small molecules that activate or repress transcription depending on the needs of the cell and substrate availability

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25
Q

What is a lac operon?

A

An inducable operon that contains the genes necessary to acquire and process lactose from the environment.

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26
Q

Why are lac operons useful for E coli bacteria?

A

It can hydrolyse lactose products of glucose and galactose can be used as a respiratory substrate.

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27
Q

What are structural genes?

A

proteins that have a cellular function

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28
Q

What are regulatory genes?

A

code for proteins that control the expression of structural genes

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29
Q

What is lacZ

A

structural genes that code for B-galactosidase which hydrolyses lactose

30
Q

What is lacY

A

structural gene that codes for lactose permease which allows lactose to enter the bacterial cell wall

31
Q

What is lacO

A

the operator

32
Q

What is lacI

A

a regulatory gene located near the operon and codes for a repressor protein that prevents transcription of structural genes in the presence of lactose.

33
Q

What happens when no lactose is present?

A

-regulatory gene is transcribed and produces the lacI repressor protein
-lacI binds to the operator region (lacO)
-RNA polymerase is unable to bind to the promoter region so no enzymes are made
-this prevents transcription of the structural genes

34
Q

What happens when lactose is present?

A

-lactose binds to the lacI repressor protein
-this alters the 3D shape so it cant bind to the lacO
-RNA polymerase binds to the promoter region
-transcription occurs of the lacZ and lacY and enzymes are synthesised.

35
Q

What is the role of cAMP?

A

As the binding of RNA polymerase still only results in a relatively slow rate of transcription, cAMP increases this process to produce the required quantity of enzymes to metabolise lactose efficiently. This is achieved by the binding of CRP to cAMP

36
Q

What happens if both glucose and lactose are present?

A

It will still be glucose that is metabolised as it is the preferred respiratory substrate

37
Q

What are transcription factors?

A

proteins or short non coding pieces of RNA that control which genes are switched on/off
-are involved in the regulation of gene expression at a transcriptional level

38
Q

How is the access of transcription factors to the underlying DNA regulated?

A

DNA is folded around the histone proteins because they’re positively charged and the DNA is negatively charged. They create nucleosome complexes so nucleosomes physically regulate the access of transcription factors to the underlying DNA.
Histones can be modified to increase or decrease the degree of packing.

39
Q

What does methylation do?

A

Methylation of DNA and histones causes DNA to pack tightly together preventing transcription factors from biding to the DNA

40
Q

What does acetylation do?

A

The addition of acetyl groups reduces the positive charge on histones causing the DNA to coil less tightly allowing transcription factors to bind to DNA and genes be expressed

41
Q

What are epigentics?

A

Used to decribe the control of gene expression by the modification of DNA

42
Q

What can occur at post transcriptional level?

A

RNA spilicing, alternative splicing, RNA stability

43
Q

What is RNA splicing?

A

After transcription in eukaryotic cells, the RNA transcript often contains introns which are removed prior to translation. The introns are removed by splicing before the RNA departs from the nucleus in order to produce mature mRNA

44
Q

What are introns?

A

regions that don’t code for a protein

45
Q

What are exons?

A

regions that do code for a protein

46
Q

What is alternative splicing?

A

-Allows different protein products to be produced from 1 gene when different combinations of introns and exons are sometimes removed from the transcript
-This allows eukaryotes to control the production of different proteins in different cells or at different stages of development

47
Q

What is RNA stability?

A

-the length of time for which RNA resides in the cytoplasm can be altered to control the overall amount of protein that is synthesised
-RNA stability can be increased leading to longer amounts of time in the cytoplasm and more protein synthesis
-it is controlled by RNA binding proteins and micro RNAs.

48
Q

What is post translational level controlled by?

A

proteins that bind and initiate the process of the modification of proteins that have been syntheisised

49
Q

What is the rpocess of post translational level?

A

1)signalling molecule binds to a receptor on the plasma membrane of target cells
2)transmembrane is activated which then activates a G protein
3)the g protein activates adenyl cyclase
4)adenyl cyclase catalyses ATP to cAMP
5)cAMP activates PKA which catalyses phosphorylation of various proteins leading to the activation of other enzymes
6)PKA phosphorylates CREB which enters the nucleus and acts as a transcription factor

50
Q

What are homeotic genes?

A

They are involved in the control of anatomical development of an organism and ensure that all structures develop in the correct location according to the body plan. Several of these contain homeobox sequences and are referred to as homeobox genes

51
Q

What are homeobox sequences?

A

-180 base pair sequence
-are a regulatory gene so involved in regulatory patterns of anatomical development in animals, plants and fungi
-the homeobox sequence codes for the homeobox domain

52
Q

What is the homeobox domain?

A

-allows homeobox genes to bind to DNA
-the homeodomain sequence folds into a particular shape and bonds to DNA to regulate transcription of adjacent genes

53
Q

What are homeobox genes?

A

they are highly conserved as they are similar in all organisms across a wide range of evolutionary distances

54
Q

What are hox genes?

A

-a particular type of homeobox gene
-regulate embryo development along the anterior posterior axis(head to tail) which causes colinearity (sequential and temporal development of body parts) as they control which body parts grow where and when
-code for homeodomain proteins
-act in the nucleus as transcription factors for activation of other genes that promote mitosis, apoptosis and cell migration
-the order of hox genes along the chromosome corresponds to the order they are expressed
-are only present in animals

55
Q

What are hox genes regulated by?

A

mRNA from the egg cytoplasm

55
Q

How many hox genes do humans have in total?

A

39

55
Q

What are body plans usually represented as?

A

cross sections through the organism showing the fundamental arrangement of tissue layers

56
Q
A
57
Q

What do hox genes in the thorax control

A

development of wings, limbs or ribs

58
Q

What have the individual vertebrae developed from?

A

Segments in the embryo called somites

59
Q

What are somites?

A

they are directed by hox genes to develop in a particular way depending on their position in the sequence

60
Q

What is radial symmetry?

A

have no left or right side just a top and bottom
seen in diplobastic animals e.g jellyfish

61
Q

What is bilateral symmetry

A

they have left and right sides and a head and tail
seen in most animals

61
Q

What is asymmetry

A

seen in sponges where there are no lines of symmetry

62
Q

What is the hayflick limit?

A

Where normal body cells can only divide a certain amount of cells before dying
Is usually around 50 cells

63
Q

What do cyclins do?

A

-The release of cyclins regulate the cell cycle
-initiate and drive each part of the cell cycle
-Cyclins activate cyclin dependent kinases (CDK)
-Each cyclin tends to remain at a low concentration within the cell until its phase of action

64
Q

What are CDKs

A

enzymes that are targeted to specific proteins involved in the relevant stage of the cell cycle

65
Q

What is apoptosis?

A

the programmed death of cells occurring as a regulated and essential part of an organisms development and growth
apoptosis of the connecting cells between digits allow the individual digits to form

66
Q

How does apoptosis prevent the spread of infection?

A

infected cells can initiate apoptosis in order to exterminate any infectious agents that they may be hosting

67
Q

Describe the process of apoptosis

A

1)signals to begin apoptosis can be external or internal to the cell
2)enzymes break down the cytoskeleton in the cell
3)cytoplasm becomes tightly packed with organelles
4)cell surface membrane changes and blebs form (small protrusions)
5)chromatin condenses, nuclear envelope breaks and DNA breaks into fragments
6)cell breaks into vesicles which are ingested by phagocytic cells
7)no trace of the original cell is left

68
Q

What factors affect the expression of regulatory genes?

A

stress-homeostatic balance within an organism is upset. could be due to a release of hormones, psychological stress, light intensity or temperature change

drugs-drug thalidomide was given to pregnant women in the 1950s to treat morning sickness and was later discovered to prevent normal expression of a particular hox gene so babies were born with shortened limbs

Biology (13 decks)

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