Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

H2 biology!!! > chapter 12: genetics of bacteria > Flashcards

chapter 12: genetics of bacteria Flashcards

You may prefer our related Brainscape-certified flashcards:
AP® Biology flashcards Biology 101 flashcards
1
Q

what is bacteria?

A
  • bacteria are prokaryotes
  • prokaryotic cells do not have membrane bound organisms
  • eg. endoplasmic reticulum, golgi apparatus and mitochondria
  • bacteria are microscopic, unicellular organisms that exist in different shape and sizes
  • they are small and unicellular but well organised
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

structure and organisation of prokaryotic genome

what is a genome?
and how is a prokaryotic genome different compared to a eukaryotic genome?

A
  • a genome is the complete set of genetic material in an organism
  • the prokaryotic genome is of smaller size and consists of lesser genes compared to eukaruotic genome
  • the two components that make up the bacterial genome:
  • plasmids and chromosomes
  • ( which are both circular and double stranded)
  • prokaryotes are typically haploid (a single copy of allele per gene)
  • due to haploidy, mutations have immediate effect
  • (no masking by dominant alleles: mutations will be expressed in the phenotype)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

describe the structure of a bacterial chromosome.

theres 5

A
  1. each bacterium contains one chromosome which is made of a double-stranded, circular DNA molecule
    - there is usually a single origin of replication
  2. since bacteria are prokaryotes, their DNA is not enclosed by a membrane
    - the chromosome is found within a region of the cytoplasm known as the nucleoid
    - transcription of a gene and translation fo its mRNA can occur at the same time
  3. genetic information carried by the chromosome is necessary for the survival of bacteria
    - eg. genes encode enzymes required for transcription and translation and the genes do not contain introns
  4. bacterial chromosomal DNA is associated with DNA binding proteins (histone like proteins)
    - proteins contain positively charged amino acids that can bind to the negative charges of the phosphate groups in DNA
    - the proteins are structurally similar to histones
  5. bacterial chromosome is highly condensed
    - DNA forms looped domains which are held together by these DNA binding histone-like proteins
    - looped domains further coil onto itself forming a supercoil
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

what are plasmids?

A
  • bacteria contain more than one small, circular DNA known as plasmids
  • plasmids are double-stranded, circular extrachromosomal DNA molecules
  • ( they are found outside the chromosome)
  • plasmids replicate independently of the bacterial chromosome, hence are autonomous
  • plasmids have relatively fewer genes compared to bacterial chromosomes
  • ## genes found on plasmids are not essential for survival of bacteria but give the bacteria some form of selective advantages in certain environments
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

compare the structural characteristics of PG and EG

compare the location of prokaryotic gene and eukaryotic gene

A

PG: genome not enclosed by nuclear membrane
- found in cytoplasm, aggrgated as a supercoil in the nucleoid

EG: enclosed by the nuclear membrane
- found in the nucleus in the condensed form ( chromosomes) or uncondensed form (chromatin)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

compare the structural characteristics of PG and EG

compare the form of genome

A

PG: circular double-stranded DNA

EG: linear double-standed DNA

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

compare the structural characteristics of PG and EG

compare the size of genome and the number of nucleotides base pairs

A

PG: genome size usually smaller than eukaryotes
- smaller number of genes
- number of nucleotide bp in the order of 10^6 to 10^7

EG: genome size much larger than prokaryotes
- larger number of genes
- number of nucleotide bp in the order 10^8 to 10^11

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

compare the structural characteristics of PG and EG

compare the chromosome number

A

PG: genome mostly located on 1 main chromosome

EG: genome is divided into many different chromosomes
- number of chromosomes is species-dependent

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

compare the structural characteristics of PG and EG

compare the presence of plasmids

A

PG: plasmids are present

EG: plasmids are only present in some eukaryotic cell

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

compare the structural characteristics of PG and EG

compare the ploidy number

A

PG: genome is usually haploid

EG: genome can exist as haploid, diploid or polyploid

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

compare the DNA packing of PG and EG

what proteins do the DNA in PG and EG associate with?

A

PG: DNA is associated with small amount of histone-like proteins
- (H-U and H-NS histone-like proteins)

EG: DNA is associated with large amount of histone proteins

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

compare the DNA packing of PG and EG

compare the levels of packing in PG and EG.

A

PG: lower degree of compaction compared to EG
- bacterial chromosome is supercoiled after the formation of looped domains

EG: higher degree of compaction than prokaryotic genome with more complex levels of condensation mechanism:
- nucleosomes > 30nm chromatin fibre> looped domains> chromosome

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

compare the coding and non-coding DNA in PG and EG

compare the proportion of coding and non-coding DNA

A

PG: high propotion of coding DNA in the genome with small amount of non-coding DNA
- (higher gene density)

EG: low proportion of coding DNA in the genome with high amount of non-coding DNA
- (low gene density)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

compare the coding and non-coding DNA in PG and EG

compare the types of non-coding DNA in PG and EG

A

non-coding DNA is most made up of:
PG:
- regulatory sequences (eg. promoters and operators), distal control elements are absent
-** introns are generally absent **, hence coding sequences of genes are continuous
- presence of some repetitive DNA but absence of centromeric and telomeric sequences

EG:
- **regulatory sequences **(eg. promoters and control elements)
- **introns present interspersed between exons: **coding sequence of genes are discontinuous
- large amounts of repetitive DNA including centromeric and telomeric sequences

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

compare the number of origins of replication between PG and EG

A

PG: one

EG: multiple

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

compare the organisation of the genes in PG and EG

A

PG:
- clustering of genes involved in the same metabolic pathway to form an operon
- genes in an operon are controlled by a single promoter

EG:
- genes involved in the same metabolic pathway are usually found separately on diferent chromosomes
- each gene is under the control of its own single promoter, termination sequence and other control elements

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

what is an operon?

A
  • an operon is a region on a bacterial DNA where :
  • a cluster of structural genes, encoding proteins of related functions or enzymes involved in the same metabolic pathhway are grouped together
  • the structural genes are regulated as one unit by a single promoter and an operator
  • hence genes can be transcribed together and be translated together
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

what are the components of an operon?

A
  1. a single promoter:
    - a sequence of DNA where RNA polymerase recognises and binds to initate transcription
  2. an operator: a sequence of DNA that serves as the binding site for repressor protein. it controls the binding of RNA polymerase to the promoter, acting as an on-off switch for transcription

the operator does not allow transcription of structural genes in operon when:
- when the repressor protein binds to the operator
- it physically blocks the binding of the RNA polymerase to the promoter, thus preventing transcription of structural genes in operon

the operator allows trancription of structural genes in operon when
- the repressor brotein is not bound to the operator
- RNA polymerase can bring to the promoter, allowing the transcription of structural genes in operon

  1. structural genes: is a region of DNA that codes for a protein or a RNA molecule that forms part of a structure or has an enzymatic function
    - (eg lacY, lacZ, lacA but excludes lacI)
    - the structural genes of an operon are controlled by the same promoter and the genes are transcribed to form a single mRNA molecule known as polycistronic mRNA
  • a polycistronic mRNA is a single mRNA molecule that codes for more than one protein
  • this polycistronic mRNA is translated to distinct polypeptides that are functionally related enzymes or proteins of a single metabolic pathway
  • this is possible because the mRNA is punctuated with start and stop codon that signal where translation for each polypeptide begins and ends
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

what are the advantages of grouping genes together in an operon?

A
  • allows the transcription of genes to be turned on and off as one transcriptional unit
  • permitting the rapid synthesis of related gene products as and when needed
  • to rapidly adapt to environmental changes
  • this provides selective advantage over cells which cannot regulate their gene expression
  • proteins and enzymes are synthesised only when needed, preventing the wastage of cell’s energy and resources
  • bacteria having different operons are able to switch on the genes of different enzymes that break down a variety of different sugars
  • thus, bacteria are able to use a variety of cugars depending on the availibility of the sugars
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

what are regulatory genes

A

regulatory gene: is a region of DNA that codes for a specific regulatory protein (activator or repressor) that controls the expression of the structural genes

  • regulatory genes are not part of the operon and is located at another portion of the bacterial chromosome, away from the operon
  • it has its own promoter
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

what are regulatory proteins?

A
  • a regulatory protein is encoded by regulatory gene that either stimulates or inhibits transcription
  • activators stimulate transcription by enhancing RNA polymerase binding to the promoter
  • repressors inhibit transcription by preventing RNA polymerase from binding to the promoter

regulatory proteins are allosteric proteins that have DNA binding domain and an allosteric site for a specific molecule
- allosteric proteins can adopt two alternative shapes: active and inactive
- binding of a specific allosteric molecule can alter the 3D shape or conformation of the protein, making it either active or inactive
- an active regulatory protein has a 3D shape of its DNA binding domain complementary to the shape of the specific sequence of bases on the DNA that it is supposed to bind to

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

what is a regulatory sequence

A
  • it is a segment of DNA where regulatory proteins bind to stimulate or inhibit transcription
  • it is neither transcribed nor translated
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

what is the difference in the function of regulatory genes and structural genes?

A

regulatory genes: codes for proteins that regulate expression of structural genes

structural genes: code for proteins or RNA molecules that forms part of a structure or has an enzymatic function

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

what is the difference in the organisation of regulatory genes vs structural genes in a bacterial genome?

A

regulatory genes: they are not grouped together
- genes are located some distance away from operon

structural genes: genes that encode proteins that function in the same metabolic pathway lie adjacent to one another
- they are grouped together in an operon

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

describe the difference in the control by promoter for regulatory genes vs structural genes

A

regulatory genes: each regulatory gene has its own promoter

eukaryotic gene: structural genes are regulated simultaneously as one unit by a single promoter

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

what is the difference in the roles of the product from a regulatory gene vs a structural gene

A

regularory genes:
- activator proteins that stimulate transcription
- repressor proteins that inhibit transcription

structural genes:
- proteins involved in the same metabolic pathway that have either catabolic or anabolic functions

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

in a repressible system, transcription of genes in operon is usually..

A

ON!

remember RON
Repressible system ON

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

in an inducible system, the transcription of genes in operon is usually…

A

OFF!

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

REPRESSIBLE SYSTEM OF GENE REGULATION

what is an example of a repressible system?

A

trp operon!

E coli synthesises the amino acid trptophan from a precursor molecule
- the genes in trp operon encode enzymes involved in the synthesis of tryptophan

  • the trp operon is a repressible operon because
  • transcription of genes in the operon is usually on/ expressed as amino acid tryptophan is absent from the environment
  • the presence of tryptophan as the end-product of the pathway then represses (off) the transcription of the genes in the operon
  • this is to prevent the wastage of the cell’s resources in producing a substance which is already present in the environment
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

what are the features of the Trp operon?

A

-** a single promoter and operator** which control the transcription of the structural genes as one unit
- five structural genes: trp E, trp D, trp C, trp B, trp A
- that encode enzmes required for the synthesis of tryptophan are grouped together into an operon

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q

describe the regulatory gene of the Trp operon.

A

TrpR gene: encodes an allosteric regulatory protein known as trp repressor
> the trp repressor can addopt either an active or an inactive shape
> it is always synthesised in its inactive form

  • in its active form, the trp repressor binds to the operator
  • (the shape of the DNA binding domain on the trp repressor is complementary to the shape of the sequence of bases on the operator)
  • it physically blocks the binding of the RNA polymerase to the promoter and prevents transcription of structural genes, thus switching off the trp operon
  • however, the trp repressor is synthesised in an inactive form with little affinity for the trp operator
  • hence, transcription is usually ON as there absence of tryptophan in the encironment most of the time
  • the binding of a co-repressor (tryptophan) to the allosteric site of trp repressor changes the repressor to an active conformation
  • the active repressor then binds to the operator
  • thus transcription of structural genes in trp operon is prevented
32
Q

what does C A R stand for?

A

Co-repressors Activate Repressors

33
Q

in the absence of tryptophan, …

A
  • the inactive trp repressor does not bind to the operator
  • RNA polymerase can bind to the trp promoter
  • structural genes within the operon are transcribed
  • the mRNA formed will be translated to produce enzymes involved in the synthesis of tryptophan
  • ( the operon is being switched on)
34
Q

in the presence of trytophan….

A
  • in the presence of tryptophan, it acts as the co-repressor and binds to the allosteric site of the inactive trp repressor protein
  • this alters the tertiary structure of the inactive repressor
  • now adopting an active shape and thus can bind to the operator
  • binding of the active repressor to the operator blocks the binding of RNA polymerase to the promoter
  • inhibiting transcription of structural genes involved in tryptophan synthesis
  • the operon is being switched off
35
Q

trp

in a repressible system
- transcription of genes is usually ________ but can be inhibited by the presence of a ________
- the co-represssor is usually the ________ of an ________ pathway
- the enzymes produced in a repressible system are known as repressible enzymes as their synthesis are inhibited in the presence of a co-repressor
- repressible enzymes usually function in anabolic pathways, which synthesise essential end products from raw materials
- by suspending production of end product when it is present in sufficient quantity, the cell can ________________________

A

in a repressible system
- transcription of genes is usually on/ expressed but can be inhibited by the presence of a co-repressor
- the co-represssor is usually the end product of an anabolic pathway
- the enzymes produced in a repressible system are known as repressible enzymes as their synthesis are inhibited in the presence of a co-repressor
- repressible enzymes usually function in anabolic pathways, which synthesise essential end products from raw materials
- by suspending production of end product when it is present in sufficient quantity, the cell can allocate its organic precursors and energy for other uses

36
Q

what is an inducible system of gene replication?

A
  • in an inducible operon, transcription of structural genes is usually OFF as the repressor is synthesised in the active form
  • active repressor binds to the operator and inhibits transcription
  • transcription can be stimulated when an inducer binds allosterically to the active repressor
  • this alters the tertiary structure of the repressor, now adopting an inactive shape and thus cannot bind to the operator
  • RNA polymerase can now bind to the promoter, leading to the transcription of structural genes
  • (operon being switched on)
37
Q

what does I I R stand for

A

Inducers
Inactivate
Repressors

38
Q

what is an example of inducible systems?

A

lac operon
- E coli is able to metabolise the disaccharide lactose into glucose and galactose
- the genes in lac operon encode proteins that are involved in the breaking down of lactose to glucose

lac operon is an inducible operon because
- the transcription of genes in the operon is usually off as lactose is absent in the environment most of the time
- however, when lactose is added to the bacteria’ environment, transcription of structural genes in the operon is switched on
- so that the three enzymes that are required for the metabolism of lactose can be produced

39
Q

what are the features of the Lac operon?

A
  • a single promoter and operator which control the transcription of the structural genes as one unit

structural genes: transcription unit in the lac operon contains 3 structural genes grouped together, which encode enzymes required for the breakdown of lactose
1. lacZ: encodes for β-galactosidase, the enzyme that hydrolyses lactose into glucose and galatose
2. lacY: encodes for permease, a membrane protein required for the transport of lactose into the bacterial cell
( cuz lactose is a large molecule that cannot diffuse through the phospholipid bilayer)
3. lacA: encodes galactoside acetyltransferase/ transacetylase, an enzyme whose function in lactose metabolism is still unclear

CAP binding site: a DNA region located within the promoter
- it is the binding site for the catabolite activator protein (CAP), an allosteric regulatory protein of the lac operon
- the binding of active CAP to the CAP binding site bends the DNA
- which makes it easier for RNA polymerase to bind to the promoter, increasing the rate of transcription of lac Z, Y, A structural genes in the operon

40
Q

regulatory genes of Lac operon

what is the Lac I gene?

A

Lac I gene: a regulatory gene that lies upstream of the lac operon and encodes for an allosteric regulatory protein, lac repressor

  • the lac I gene has its own promoter and is constitutively (always) expressed, continually producing small amounts of lac repressor protein
  • in its active form, the lac repressor binds to the operator, physically blocking the binding of the RNA polymerase to the promotor and prevents transcription of structural genes, thus switching off the lac operon
  • The lac repressor protein is synthesized in an active form with high affinity for the lac operator, which usually inhibits transcription.
  • This is because, in the absence of lactose in the environment, the repressor remains bound to the operator
  • the binding of the inducer (allolactose) to the allosteric site of the lac repressor changes the repressor to an inactive conformation
  • the repressor is unable to bind to the operator
  • thus this allows transcription of the structural genes in lac operon
41
Q

regulatory genes of Lac operon

what is the CAP gene?

A

CAP gene: encodes for an allosteric regulatory protein, catabolite activator protien

  • the binding of active CAP to CAP bindign site bends the DNA, which makes it easier for RNA polymerase to bind to the promoter
  • increasing the rate of transcription of lac Z, Y, A structural genes in the operon
42
Q

in the ABSENCE of lactose…

A

in the absence of lactose..
- the active lac repressor binds to the operator
- RNA polymerase is prevented from binding to the promoter, preventing transcription
- structural genes lac Z, Y, A within the operon are not transcribed
(the operon is being switched off)

43
Q

in the PRESENCE of lactose…

A
  1. when lactose is present in the bacteria’s environment, the lactose first enters the cells via small number of permeases embedded on the cell’s surface membrane
    - once inside the cell, small amount of lactose is converted to form allolactose
  2. allolactose acts as an inducer by binding to the allosteric site of the active lac repressor
  3. this alters the tertiary structure of the repressor, now adopting an inactive shape and thus cannot bind to the operator
    - this exposes the promoter site
  4. RNA polymerase can now bind to the promoter
    - structural genes lac Z, Y, A are transcribed
    - the mRNA formed is translated to produce β-galatosidase, permease and transacetylase enzymes to break down lactose into glucose and galactose
44
Q

hence in an inducible system,
- transcription of genes is usually _____but can be stimulated by the presence of an inducer
​
- the inducer is usually the ________ ( in this case, lactose) of a catabolic pathway.
​
- the enzymes produced in a inducible system are known as inducible enzymes as their synthesis are stimulated in the presence of an __________
​
- inducible enzymes usually function in ________, which break down complex molecules into simpler molecules
- by producing appropriate enzymes only when the nutrients are availible, the cell avoids wastage of resources to make proteins unnecessarily

A

hence in an inducible system,
- transcription of genes is usually OFF but can be stimulated by the presence of an inducer

  • the inducer is usually the substrate ( in this case, lactose) of a catabolic pathway.
  • the enzymes produced in a inducible system are known as inducible enzymes as their synthesis are stimulated in the presence of an inducer
  • inducible enzymes usually function in catabolic pathways, which break down complex molecules into simpler molecules
  • by producing appropriate enzymes only when the nutrients are availible, the cell avoids wastage of resources to make proteins unnecessarily
45
Q

how do bacteria reproduce?

A
  • bacteria cells reproduce asexually via binary fission, a process in which a single bacteria cell divides into two geneticlly identical daughter cells
  • this is an asexual process as production of new cells involves only a single parent
  • eukaryotes can reproduce via sexual reproduction
  • they have short generation time
  • under optimum condition, bacteria cells can divide every 1-3 hours, some species can produce a new generation in every 20 min
  • bacterial population growth is said to be exponential
  • the number of bacteria cell doubles every one generation
  • a single bacteria cell divides into 2 cells, which the divide into 4, 8, and 16 and so on
46
Q

describe the process of binary fission

A
  1. the single bacterium chromosome (double stranded DNA) attaches to the cell surface membrane at the origin of replication
  2. DNA undergoes semi conservative replication
    - double stranded DNA molecule separates at the origin of replication, forming a replication bubble
    - each separated DNA strand acts as a template for synthesis of a complementary daughter strand
  3. from the origin of replication, DNA replication progresses bidirectionally around the circular chromosome until the entire chromosome has been reproduced
    - the newly synthesised DNA’s origin of replication is also attached to the cell surface membrane
  4. as the bacterial cell elongates and grows in size, the two bacterial chromosomes are separated and end up in opposite poles of the cell
  5. the cell surface membrane invaginates and new cell wall material is synthesised
    - the original cell is divided into two genetically identical daughter cells
47
Q

what causes the genetic variation in bacteria? compared to in a eukaryotic cell.

A
  • since binary fission is an asexual process, the daughter cells produced would be genetically identical to the parental cells
  • however, genetic variation in bacteria can still occur via mutation (insertion, deletion, substitution) and genetic recombination
  • however in eukaryotic cell, sexual processes of meiosis and random fertilisation of gametes generate genetic variation
  • genetic variation enhances the ability of an organism to remain adapted in its environment
47
Q

what is genetic recombination and how does it help in bacteria cells?

A

genetic recombination: refers to the combining of DNA from two individuals into the genome of a single individual

  • it occurs when foreign DNA from a donor cell is introduced into the recipient cell
  • the transferred donor DNA may then be introduced into the recipient’s chromosomal DNA
  • genetic recombination increases genetic variation in bacteria cells
48
Q

what are the 3 mechanisms of genetic recombination?

A
  1. transformation
  2. transduction
  3. conjugation
49
Q

genetic recombination in bacteria

what is transformation?

A

transformation: it is the uptake of a foreign naked DNA molecule from the bacterium’s surrounding medium/ external environment and the integration of theis molecule into its own DNA
- thus resulting in the change of the recipient bacterial cell’s genotype

  • foreign DNA segments can be integrated into a homologous region found on the recipient bacterial chromosome, via homologous recombination
  • the resultant transformat cell will now express genes from this new segment it has received and pass them on to all subsequent daughter cells by binary fission
  • the size of the donor DNA is usually smaller than the recipient bacterial chromosome
  • this facilitates integration into bacterial chromosome
50
Q

genetic recombination in bacteria

what is the detailed process of transformation?

A
  1. The binding of foreign donor DNA from lysed bacterial cells to the cell surface of a competent bacterial cell is facilitated by DNA-binding proteins.
  2. a nuclease degrades one strand of the double-stranded DNA fragment while the other single-stranded DNA enters into the recipient cell
  3. After entering the cell, the single-stranded DNA binds to a competence-specific protein, which likely protects it from degradation by nucleases until it reaches the bacterial chromosome.
  4. the single-stranded DNA is then integrated into the bacterial host DNA by means of RecA proteins via homologous recombination
    - this involves breakage and reunion of homologous DNA segments
  5. the recipient cell is called a recombinant as it contains DNA from two different cells
    - the cell is said to be transformed
51
Q

genetic recombination in bacteria: transformation

transformation only allows the uptake of foreign DNA from the ____ species or ____ species

A

transformation only allows the uptake of foreign DNA from the same species or related species

52
Q

genetic recombination in bacteria: transformation

the foreign DNA may come from cells that have ____ and subsequently ____, releasing DNA into the environment

A

the foreign DNA may come from cells that have died and subsequently lysed, releasing DNA into the environment

53
Q

genetic recombination in bacteria: transformation

bacteria cells that can uptake DNA and be transformed are termed ____ cells
- these ____ cells carry genes that codes for competence-specific proteins and DNA binding proteins

A

bacteria cells that can uptake DNA and be transformed are termed competent cells
- these competent cells carry genes that codes for competence-specific proteins and DNA binding proteins

54
Q

genetic recombination in bacteria: transduction

what is transduction?
(generalised transduction and specialised transduction)

A

transduction: is the process by which DNA is transferred from one bacterial cell (donor) to another (recipient) by bacteriophages
- and is later integrated into the bacterium’s genome of the recipient cell via genetic recombination

**generalised transduction:
**- involved lytic bacteriophages (eg. T4 phages)
- a bacteriophage transfers any random segment of the host baterial chromosomal DNA to another bacterium

**specialised transduction:
**- involves temperate bacteriophages (lambda phage)
- a bacteriophage transfers a specific set of baterial genes from host to another bacterium

55
Q

describe the detailed process of generalised transduction.

A
  1. a lytic phage infects and injects its phage DNA into a donor bacterium
  2. when a phage undergoes the lytic cycle, phage enzymes are produced that hydrolses/ degrade donor bacterial DNA into smaller fragments
  3. occasionally, during the virus assembly stage, a small piece of the bacterium’s degraded DNA iss accidentally packaged within the phage capsid rather than the phafe DNA
    - hence this phage particle carries bacterial DNA but not phage DNA
    - these phages are known as transducing phages
  4. upon lysis of the bacterium, the released transducing phages can attach to anothe new acterium ( recipient) and inject the piece of bacterial DNA acquired from the previous host cell (donor)
  5. the original bacterial DNA can then be integrated/ inserted into the recipient bacterial chromosomal DNA via homologous recombination
56
Q

describe the detailed process of specialised transduction

A
  1. a temperate bacteriophage infects and injects its phage DNA into a donor bacterium and integrates its phage DNA at a specific site into the bacterium’s chromosomal DNA
    - to form a prophage, during the lysogenic life cycle of virus
  2. during spontaneous induction, prophage is excised from the donor bacterium’s chromosome
    - sometimes a small specific region of donor bacterial DNA that is adjacent to the prophage insertion site
    - is excised together due to an error in the excision
  3. due to stress, the lytic life cycle of the virus is triggered
    - during viral assembly, the phage DNA together with the adjacent bacterial DNA will be packaged into phage capsid
  4. upon lysis of the donor bacterium, the released specialised transducing phages can infect another bacterium, the previous bacterial genes are injected along with the phage’s genome
  5. the original bacterial DNA can then be inserted into the recipient bacterium’s chromosomal DNA via homologous recombination
57
Q

what is conjugation?

A
  • it is the process by which two bacterial cells make direct contact with each other and DNA is directly transferred from one donor cell to another recipient cell
  • through a temporary conjugation tube/ cytoplasmic bridge between the two cells
  • DNA transfer is unidirectional: the donor cell donating DNA, and its recipient receiving the genes
  • the ability to serve as a donor is determined by the presence of a piece of DNA known as the F factor or fetility, which contain genes coding for the production of the sex pilus during conjugation
  • bacteria containing the F factor are able to form the sex pilus and thus function as DNA donors during conjugation
  • bacteria lacking the F factor function as DNA recipients during conjugation
  • An F factor can exist either independently of the bacteria chromosome as a F plasmid or integrated into the bacterial chromosome
  • F plasmids are small, circular, extrachromosomal DNA, with their own origin of replication
58
Q

conjugation

TRUE OR FALSE:
sex pilus becomes the conjugation tube

A

FALSE!!!
sex pilus facilitates the formation of the conjugation tube

59
Q

what is the detailed process of conjugation?

A
  1. conjugation begins when the sex pilus made by F+ donor cell makes direct contact on the surface of a F- recipient cell
  2. the sex pilus then retracts, pulling the two cells together into physical contact via a conjugation tube
    - ( a temporary cytoplasmic mating bridge) that connects the two cells temporarily
  3. one strand of the F plasmid is cut by the endonuclease enzyme- encoded by genes in F plasmid at a specific point
    - known as the origin of transfer and the nicked single strand of F plasmid begins to enter the F- recipient cell through the conjugation tube
  4. as the transfer occurs, each original strand of F plasmid in the donor and recipient cell acts as a templace for the synthesis of a complementary strand
    - thus foring a new double-stranded F plasmic in both donor and recipient cells
  5. at the end of process, F- cell becomes F+ cell, the conjugation tube is then broken down
60
Q
  • some bacterial cells contain other plasmids
  • eg R plasmids, which contain genes that encode for the formation of the ____
  • hence, these bacteria can also trasnfer DNA from one cell to another via _____
  • R plasmids may contain genes that allow bacteria cells to gain antibiotic resistance, resistance to heavy metals, resistance to drugs and even the ability to utilise metabolites
A
  • some bacterial cells contain other plasmids
  • eg R plasmids, which contain genes that encode for the formation of the sex pilus
  • hence, these bacteria can also trasnfer DNA from one cell to another via conjugation
  • R plasmids may contain genes that allow bacteria cells to gain antibiotic resistance, resistance to heavy metals, resistance to drugs and even the ability to utilise metabolites
61
Q

what are antibiotics used for

A
  • they are used to treat bacterial infections, preventing bacteria from reproducing and stopping infection
  • antibiotics can be bactericidal (kill target organism) or bacteriostatic (inhibit or felay bacterial growth and replication)
  • ## some antibiotics can be both depending on the dose, duration of exposure and the state of invading bacteria
62
Q

what are broad spectrum antibiotics and what are some examples?

Gram-positive bacteria have a thicker ____ in the bacterial cell wall but lack an ____
- but conversely, gram-negative bacteria have a much thinner ____ and are surrounded by an outer membrane

  • despite their thicker peptidoglycan layer, gram-positive are more vulnerable to antibiotics than gram-negative bacteria
  • due to the absence of the outer membrane that makes it more difficult for antibiotics to enter the cell
A
  • active against a wide range of both Gram-positive and gram-negative organisms

Gram-positive bacteria have a thicker peptidoglycan layer in the bacterial cell wall but lack an outer membrane
- but conversely, gram-negative bacteria have a much thinner peptidoglycan layer and are surrounded by an outer membrane

  • despite their thicker peptidoglycan layer, gram-positive are more vulnerable to antibiotics than gram-negative bacteria
  • due to the absence of the outer membrane that makes it more difficult for antibiotics to enter the cell

examples: tetracyclines, fluoroquinolones

63
Q

what are narrow spectrum antibiotics

A
  • primarily only useful against a small range of or particular species of microorganisms

examples:
1. glycopeptides are only effective against gram-positive bacteria
2. polymixins are usually only effective against gram negative bacteria

64
Q

read and scan the notes for the rest of the antibiotics because any more than 65 cards is madness.

A
65
Q

why can’t antibiotics be used to treat viral diseases?

A
  • antibiotics do not affect viruses as a virus lacks cell structure and has no metabolism of its own to be disrupted by antibiotics
  • viruses use metabolic machineries of host cells that are not affected by antibiotics
  • thus they can continue their reproductive cycle
66
Q

what happens when antibiotics inhibit cell wall synthesis? and what is an example of it?

A
  • the bacterial cell is surrounded by a peptidoglycan cell wall
  • the mechanical strength of the cell wall is critical to a bacterium’s ability to survive in changing osmotic pressures
  • inhibition of cell wall synthesis can result in changes to the cell shape and size, which may ultimately lead to cell lysis
  • (due to high osmotic pressures within bacterium, water entry causes osmotic lysis)
  • eg. Penicillin acts as a competitive inhibitor to transpeptidases and blocks the cross linking of peptidoglycan units by inhibiting peptide bond formation
    > inhibits bacterial cell wall synthesis by disrupting peptidoglycan synthesis
67
Q

what happens when antibiotics inhibit protein synthesis? and what are some examples?

A
  • drugs that inhibit protein synthesis are among the broadest classes of antibiotics
  • the process of mRNA translation consists of three phases ( initiation, elongation and termination) and involves the ribosome and translation initiation factors
  • initiation and elongation may be inhibited by antibiotics
  • antibiotics may also result in protein mistranslation by promoting tRNA mismatch with mRNA codon

eg. - 50S inhibitors such as linocosamide block the access of peptidyl-tRNA to the ribosome, subsequently blocking elongation, and eventually triggering dissociation of peptidyl-tRNA
- 30S inhibitors such as tetracyclines may work by blocking access of aminoacyl-tRNAs to the ribosome
- aminoglycosides can induce an alteration in the conformation of the complex formed between an mRNA codon and its activated aminoacyl-tRNA at the ribosome, promoting tRNA mismatching which can result in protein mistranslation

68
Q
  1. Nucleic Acid Synthesis Inhibition:
    • Bacteria need to make DNA (for replication) and RNA (for protein production).
    • For this, they rely on enzymes like topoisomerases to manage DNA supercoiling (twisting and untwisting DNA strands).
    1. Role of Topoisomerases:
      • Topoisomerases cut and rejoin DNA strands, allowing them to untangle during replication and transcription (DNA to RNA).
      • Without functioning topoisomerases, bacteria can’t copy their DNA or make mRNA.
    2. How Antibiotics Work:
      • Quinolone antibiotics (like ciprofloxacin) target DNA gyrase and topoisomerase IV, two key bacterial topoisomerases.
      • These antibiotics prevent the enzymes from doing their job, causing double-stranded DNA breaks.
    3. Result:
      • DNA replication stops.
      • The bacterial cell can’t grow (bacteriostasis) and eventually dies from the accumulated damage.

In summary, quinolones disrupt bacterial DNA processes by targeting enzymes critical for DNA handling, stopping the bacteria from reproducing or functioning.

A

you can do this!

69
Q

antibiotics inhibition of RNA synthesis.

A
  1. Targeting RNA synthesis:
    • Rifamycin drugs inhibit transcription, the process where RNA is synthesized from a DNA template.
    • Specifically, they bind to RNA polymerase, the enzyme responsible for building RNA strands. This prevents the bacteria from producing essential RNA molecules needed for protein synthesis and other vital functions.
    1. Effectiveness against mycobacteria:
      • Rifamycin drugs are highly effective against Mycobacterium tuberculosis, the bacterium that causes tuberculosis.
      • They induce cell death in these bacteria, making them one of the first-line treatments for tuberculosis.
70
Q

how does antibiotics inhibit the cell membrane function?

A
  • a disruption in the cell membrane could result in leakage of important solutes essential for the cell’s survival
  • however, as both eukaryotic and prokaryotic cells have cell membrane, this class of antibiotics are poorly selective and can often be toxic for systemic use in the mammalian host
  • most clinical usage is therefore limited to topical applications
    (eg. creams for skin infections
71
Q

antibiotics: the inhibition of other metabolic processes
- antibiotics act on selected cellular processes essential for the survival of bacterial pathogens such as the folic acid pathway
- folic acid is a necessary step for bacteria to produce precursors important for DNA synthesis

A

yum yum eat them up!

72
Q

structure of bacteria: cell wall

A
  • bacteria cells have a peptidoglycan cell wall
  • peptidoglycan is a complex molecule consisting of a network of modified sugar polymers, cross- linked by short polypeptides
  • this is different from the cell wall of plants, which is made up of cellulose
  • some bacteria cells have a capsule located exterior to the cell wall
  • circular DNA and 70S ribosomes are found in the cytoplasm of bacteria cells have a
73
Q

structure of bacteria: capsule

A
  • a capsule is a sticky carbohydrate layer found outside the cell wall and is present on some bacteria
  • aids in bacteria attachment to a surface or to other individuals in a colony and also to shield the bacteria from attacks by the host’s immune system
  • also protects bacteria from dehydration
74
Q

structure of bacteria: fimbriae ((singular: fimbria)

A
  • fimbriae are short, hair-like protein appendages responsible for bacteria attachment to a surface or to one another
  • fimbriae are usually shorter and more numerous than sex pili
75
Q

structure of bacteria: flagella (singular: flagellum)

A
  • flagella are tail-like structures that enable bacteria to move/ swim
  • may be scattered over the entire surface or concentrated at one or both ends
76
Q

structure of bacteria: flagella (singular: flagellum)

A
  • flagella are tail-like structures that enable bacteria to move/ swim
  • may be scattered over the entire surface or concentrated at one or both ends

H2 biology!!! (15 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions