Chapter 6: Molecular genetics

DNA ligase

"Glues" together DNA fragments on the lagging strand by catalyzing the formation of phosphodiester bonds

what are the three main types of DNA mutations?

- base substitutions (point mutations) - insertions - deletions

How many nucleotides is required for 90 codons?

270 Each codon consists of THREE nucleotides. Therefore, we simply multiply 90 by 3 and see that it constitutes 270 nucleotides.

A segment of DNA reads as follows: 5' - ATATATGCGCACGC - 3' What is the corresponding mRNA synthesized?

5' - GCGUGCGCAUAUAU - 3' the RNA polymerase read the template DNA strand in the 3′→5′ direction, but the mRNA is formed in the 5′ to 3′ direction. Furthermore, in mRNA, the nucleotide thymine (T) is replaced with uracil (U).

How many histones are in a nucleosome?

9 histones central core: 8 (2 of each type) H2A, H2B, H3, H4 on the outside: 1 H1

which promoter regions is most likely to initiate transcription?

Adenine and thymine are less tightly bonded to each other compared to the guanine-cytosine (C-G) bond, and therefore PROMOTOR REGIONS ARE RICH IN A-T BONDS. ex. GATTAAT CTAATTA only one G-C bond which contains three hydrogens meaning the bonds are stronger and more tightly. Therefore, less G-C bonds and more A-T bonds mean transcription is more likely to occur

A virus is an infectious A. bacterium B. particle C. cell D. animal

B. particle Viruses are categorized as infectious particles because they are not alive.

sigma factor

Before transcription can occur, a sigma factor combines with prokaryotic core RNA polymerase to form RNA polymerase holoenzyme, giving it the ability to target specific DNA promoter regions.

Alternative splicing allows for which of the following? A. Cleaves mRNA to produce sticky ends B. The removal and replacement of mismatched base pairs C. Production of many proteins from a single mRNA strand D. To break off and move a piece of a chromosome

C. Production of many proteins from a single mRNA strand mRNA splicing is one of the post-transcriptional modifications that is performed in eukaryotic cells (The other two are 5' cappingand polyadenylation of the 3' end). One of the main purposes of mRNA splicing is to remove interruptions in the coding sequence known as introns, so that only the functional exons are expressed. However, it is also possible for exons to be removed during splicing. This can be done on purpose to produce different combinations of exons that allow for multiple functional proteins to be made from one mRNA strand. This is known as alternative splicing.

What is the most likely place for a transcription factor to bind to? A. Operon B. Repressor C. TATA box D. Poly-A signal

C. TATA box Transcription factors are needed in eukaryotes to help RNA polymerase bind to promoters. The TATA box is a thymine and adenine (T/A) rich sequence in many promoter sequences that transcription factors can recognize and bind to.

Topoisomerase (DNA gyrase)

Creates small nicks within the DNA double helix to relieve tension ahead of the replication fork

alternative splicing

Creation of multiple different proteins from one RNA strand produce different combinations of exons that allow for multiple functional proteins to be made from one mRNA strand.

In contrast to a prokaryotic organism, which of the following is unique to eukaryotic gene expression? A. Presence of a promoter region B. Use of RNA polymerase C. Polyadenylation of RNA transcripts D. Presence of intron sequences E. Simultaneous transcription and translation

D. Presence of intron sequences Prokaryotes do not contain introns in their mRNA. Simultaneous transcription and translation is incorrect because simultaneous transcription and translation is a characteristic unique to prokaryotes, not eukaryotes.

DNA packaging

DNA is continuously wrapped around histone complexes Histone's bonding with DNA is the first step of DNA packaging, from then on the DNA coils around the histone complex creating a nucleosome. After several repetitions, the coiled DNA becomes chromatin.

What is the goal of genome annotation? A. Determine all 3D protein structures in a genome B. Analyze heritable epigenetic changes to a genome C. Study genomic changes over the course of generations D. Locate the corresponding DNA sequence of a known protein E. Determine all coding regions of genes and their functions

E. Determine all coding regions of genes and their functions Once a gene is sequenced, it must be annotated in order to make sense of it. Genome annotation is the process of: - Identifying the locations of genes and all of the coding regions in a genome. - Determining what those genes do.

eukaryotic ribosomal subunits

Eukaryotic ribosomal subunits (60S and 40S) assemble in the nucleoplasm and are then exported from the nucleus to form the complete ribosome in the cytosol (80S). involved in protein translation

Telomerase

Extends telomeres at the ends of eukaryotic chromosomes to prevent DNA from losing information

which can increase or decrease gene expression

Histone Methylation - Adds methyl groups - Can increase or decrease transcription

increased (turns on) gene expression

Histone acetylation - Acetyl chains added to histone proteins remove positive charges Euchromatin packaging - Loosely packed DNA is accessible for transcription

decreased (turns off) gene expression

Histone deacetylation - Acetyl chains removed from histone proteins increase positive charges Heterochromatin Packaging - Tightly packed DNA prevents transcription factors from binding RNA Interference (RNAi) - RNA silencing Complex binds to mRNA, cleaving and silencing the gene DNA Methylation - Methyl groups added to nucleic acids prevent transcription factors from binding (do not get confused with histone methylation) Repressor Proteins - Repressors bound to DNA prevent RNA polymerase from binding

genome annotation

Identifying the locations of genes and all of the coding regions in a genome and determining what those genes do.

prokaryotic transcription control

In prokaryotes, transcription occurs in the cytosol. RNA polymerase opens up DNA, forming a transcription bubble.

what are the three genes contained within the lac operon that encode proteins required for lactose metabolism?

LacZ, LacY, and LacA

is transcription and translation simultaneous in prokaryotes and eukaryotes?

NO Transcription and translation are simultaneous in prokaryotes but not eukaryotes

are transcription factors a method of cell to cell communication?

NO examples of cell-cell communication: neurotransmitters, chemical signals

Primase

Places RNA primer at the origin of replication, which provides a 3' hydroxyl group to which DNA polymerase can attach free nucleoside triphosphates

why does DNA transcription require RNA polymerase?

RNA polymerase is an enzyme that synthesizes mRNA from a DNA template.

what are the two types of termination in bacteria?

Rho independent termination + Rho-dependent termination

eukaryotic transcriptional factors

Unlike in prokaryotes, eukaryotic transcription occurs in the nucleus and uses RNA polymerase II to transcribe most genes. Transcription factors are needed in eukaryotes to help RNA polymerase bind to promoters. The TATA box is a sequence in many promoters that transcription factors can recognize and bind to.

Which DNA strand would have the highest melting point?

Whichever DNA strand has the MOST G=C bonds will have the HIGHEST melting point. ex. CCGTGACC GGCACTGG

is RNA polymerase necessary for transcription in eukaryotes and prokaryotes?

YES

does eukaryotes and prokaryotes contain promotor sequences for transcription?

YES In prokaryotes, the promotor region is known as the Pribnow box and, in eukaryotes, it is known as the TATA box.

translocation

a piece of one chromosome breaks off and attaches to another chromosome. example: In a karyotype of a human embryo, it's observed that there is an unidentical banding pattern and a longer arm than usual on chromosome 12.

insertions

adding nucleotides into the DNA sequence - can shift the reading frame.

tRNA is associated to link together:

amino acids

transposes

an enzyme that shifts genes around in the genome by binding to the end of a transposon and catalyzing its movement. This is done through a cut and paste mechanism. However, transposase does not delete any specific sequences.

miRNA

are small RNA molecules that SILENCE mRNA expression as a method of post-transcriptional gene regulation by base-pairing with parts of sequences on the mRNA transcript that inhibits their translation.

silencer

binds to a repressor and subsequently decreases the expression of the gene product.

enhancer

binds to an activator and subsequently increases the expression of the gene product.

operon

cluster of related genes that are controlled as a single unit under one promoter sequence. This is a form of prokaryotic transcriptional control.

DNA helicase

enzyme that "unzips" the wound DNA double helix by breaking the hydrogen bonds between complementary purines and pyrimidines.

When allolactose is present...

it binds to and deactivates a repressor protein

transformation

it occurs when a bacterial cell takes up extracellular DNA from its environment and incorporates it into its chromosome. example: Antibiotic resistant bacteria colony A is left to sit on an agar plate. After some time, bacteria colony A is removed and antibiotic susceptible bacteria colony B is added to the plate. Bacteria colony B gains antibiotic resistance while sitting on the plate. another example: E.coli produces toxin X, a deadly substance. H. pylori does not produce toxin X. In an experiment, E.coli is allowed to sit in a solution for some time. The E.coli are then removed from the solution and H. pylori are placed inside. After some time in the solution, H. pylori are now able to produce toxin X.

transduction

occurs when virus particles transfer bacterial DNA between different bacterial hosts. a bacteriophage infects a bacterium and enters the lysogenic cycle.

point mutation and what are the three types?

one nucleotide is replaced by another. For example, instead of a codon containing an adenine, it is replaced by guanine. - silent mutations: no change in amino acid sequence. Due to "third base wobble", mutations in the DNA sequence that affect the third base of a codon can still result in the same amino acid being added to the protein. Relies on the degeneracy (redundancy) of translation. - missense mutations: single change in amino acid sequence. Can either be conservative or non-conservative nonsense mutations: single change in amino acid sequence that results in a stop codon. Results in early termination of protein (stops translation).

deletions

removing nucleotides from the DNA sequence - can shift the reading frame.

Homologous recombination

results in an exchange of genetic material between two strands of DNA that contain similar base sequences

rRNA

ribosomal RNA, which is synthesized in the nucleolus. rRNA combines with proteins to form the ribosomes found in protein translation

tRNA

transfer RNA carries an amino acid to the ribosome during protein translation

how can bacteria transfer genes horizontally?

transformation, transduction, and conjugation *NOT binary fission

A ribosome initiates the translation of an mRNA transcript. After a second aminoacyl-tRNA enters the ribosome, where does the polypeptide chain move as a new peptide bond is formed? A. A site B. P site C. E site D. Termination site

A. A site In the process of translation, aminoacyl-tRNAs (tRNA molecules carrying an amino acid) enter the ribosome at the A site. In the P site, a peptidyl-tRNA holds the growing polypeptide chain. After the new tRNA arrives at the A site, the ribosome catalyzes the formation of a peptide bond between the polypeptide chain and the new amino acid. The polypeptide chain moves from the P site tRNA and attaches to the amino acid that is bound to the tRNA on the A site. Lastly, the ribosome itself shifts down one codon along the mRNA such that the old P site tRNA (now empty) is transferred to the E site and leaves the ribosome, and the old A site tRNA (that is now holding the polypeptide chain) is moved to the new P site. During translation, after a new peptide bond is formed, the growing polypeptide chain is passed from the P site tRNA to the A site tRNA.

Which of the following best describes the mechanism of microRNA? A. Post-transcriptional regulation of gene expression B. Transports genetic information from DNA to ribosomes C. Forms components of ribosomal subunits D. Functions as catalytic ribozymes E. Base pairs with complementary DNA targets

A. Post-transcriptional regulation of gene expression A microRNA (miRNA) is a small non-coding RNA interference molecule in eukaryotes that functions in RNA silencing and post-transcriptional silencing of gene expression. miRNAs base pair with complementary sequences within mRNA molecules. As a result, these mRNA molecules are silenced by one or more of the following processes: Cleavage of the mRNA strand into two pieces Destabilization of the mRNA through shortening of its poly-A tail Less efficient translation of the mRNA into proteins by ribosomes

Which of the following mechanisms is used to turn off the expression of a gene? A. Histone acetylation B. DNA methylation C. Repressible enzymes D. Single-stranded DNA binding proteins E. Euchromatin formation

B. DNA methylation In DNA methylation, methyl groups are added to individual bases in DNA to repress their transcription. DNA methylation is also used in X-inactivation (where one copy of the two X chromosomes in female mammals is inactivated). Be careful not to confuse DNA methylation with histone methylation, which can be used to activate or repress genes, depending the location and number of the methyl groups added/removed within the histone protein. In histone acetylation, acetyl groups are added to lysine residues on histones to open up DNA and activate transcription. Histone acetylation has the reverse effect of DNA methylation. DNA methylation, histone methylation, and histone acetylation are forms of epigenetic control, where gene expression is regulated without changing the DNA sequence.

Which of the following point mutations would be most detrimental to protein function? A. Conservative missense B. Early nonsense C. Third base substitution D. Duplication E. Late insertion

B. Early nonsense There are 3 main types of DNA point mutations you need to know: - Silent mutations. One nucleotide is swapped out for another, but because of 'third base wobble' in translation, the same protein is made. These are least harmful because there is no change to the protein structure. - Missense mutations. Single change in the amino acid sequence. Depending on how critical the amino acid is, this could either have minor effects or major effects. - Nonsense mutations. Single change in amino acid sequence that stops translation. This is the most severe because the protein isn't finished.

An unedited human gene is inserted into a prokaryote to study its function. However, the prokaryote does not express the inserted gene. Which of the following is the most likely reason the prokaryote cannot express the human gene? A. Prokaryotes are unable to transcribe eukaryotic DNA B. Prokaryotes lack the ability to remove introns C. Prokaryotic ribosomes cannot translate eukaryotic mRNA D. Eukaryotic DNA contains histones that prevent transcription E. Prokaryotes use a separate genetic code to store information

B. Prokaryotes lack the ability to remove introns One of the main differences between how eukaryotes and prokaryotes manage their gene expression has to do with post-transcriptional modifications. Eukaryotes make a number of alterations to newly transcribed RNA, whereas prokaryotes tend to directly translate RNA almost right after it's been produced. One of the post-transcriptional modifications that eukaryotes perform is RNA splicing. Eukaryotic genes are composed of introns and exons. Prior to translation, a spliceosome will remove all of the introns such that the functional gene is made up of the right combination of exons. If a prokaryotic cell were to have human (eukaryotic) DNA directly inserted into its genome, this DNA would still contain its full array of introns and exons. The prokaryotic cell does not have a mechanism for splicing out introns, and therefore the human gene would not be correctly expressed.

If missing, which of the following would prevent DNA transcription from occurring? A. 80S ribosome B. RNA polymerase C. tRNA D. DNA polymerase E. rRNA

B. RNA polymerase DNA transcription requires RNA polymerase. RNA polymerase is an enzyme that synthesizes mRNA from a DNA template. There are three steps in transcription: Initiation - a promoter sequence next to the gene attracts RNA polymerase to transcribe the gene. Elongation - transcription bubble forms and RNA polymerase synthesizes mRNA in the 5' → 3' direction. Termination - a termination sequence (aka terminator) signals to RNA polymerase to stop transcribing the gene. DNA polymerase is used in DNA replication. During the S phase of the cell cycle, the DNA of a cell is duplicated with DNA polymerase to prepare the cell for mitosis. If DNA polymerase was missing, it would not prevent DNA transcription from occurring.

A scientist inserts an unedited human gene into a bacterial cell so that the function of the gene can be researched. Unfortunately, the human gene does not seem to be expressed. What is the most likely cause of this issue?

Bacteria lack the mechanisms to remove the human gene's introns The most likely cause of this issue is that the bacterium cannot undergo splicing of pre-mRNA. Prokaryotes, like bacteria, do not have the mechanisms to remove introns as mRNA in prokaryotes does not need to be processed after transcription. Splicing is an mRNA processing event unique to eukaryotes

Viruses can replicate themselves in all of the following cell types EXCEPT one. Which is the EXCEPTION? A. Leukocytes B. Lymphocytes C. Erythrocytes D. Granulocytes E. Podocytes

C. Erythrocytes Viruses are not living cells and therefore they rely on the cells they infect in order to replicate themselves, through the lytic cycle or lysogenic cycle. Contrary to sperm cells, muscle cells, T cells, and plant cells, erythrocytes lack the nuclei and organelles required to replicate nucleic acids and elaborate proteins. Because viruses depend on the use of host cell machinery to replicate, erythrocytes are invulnerable to viral infection.

how are histones and DNA attached?

Histones are positively charged while DNA is negatively charged. They attach to one another through these electrostatic interactions

DNA sliding clamp

Holds DNA polymerase to the template strand

Antibiotic resistant bacteria colony A is left to sit on an agar plate. After some time, bacteria colony A is removed and antibiotic susceptible bacteria colony B is added to the plate. Bacteria colony B gains antibiotic resistance while sitting on the plate. What phenomenon best describes what has occurred? A. Transduction B. Conjugation C. Transformation D. Mutation E. Translation

C. Transformation Bacteria are asexual organisms, which means that they do not reproduce by mating with another individual; rather, they divide by binary fission. Bacteria cannot increase genetic diversity via sexual reproduction or mating. However, bacteria are able to transfer genes horizontally (i.e. within a generation), which contributes to increased genetic diversity. Transformation is one of the three methods by which bacteria can accomplish horizontal gene transfer. Transformation occurs when a bacterial cell takes up extracellular DNA from its environment and incorporates it into its chromosome. In this scenario, bacteria colony B picked up free-floating DNA (from bacteria colony A) and incorporated it into its chromosome, thereby acquiring antibiotic resistance.

where does protein translation occur in prokaryotes and eukaryotes?

CYTOSOL

Which enzyme cleaves DNA into smaller fragments? A. Ligase B. Protease C. Helicase D. Exonuclease E. Catalase

D. Exonuclease Exonucleases are enzymes that cleave nucleotides one at a time from the end of a polynucleotide chain. This occurs via a hydrolyzing reaction that breaks phosphodiester bonds at either the 3' or 5' end. A close relative is the endonuclease, which cleaves phosphodiester bonds in the middle of a polynucleotide chain. Polyadenylation is a post-transcriptional modification of eukaryotic pre-mRNA that prevents RNA degradation by exonuclease.

The direct transfer of genetic material from one live bacterium to another is referred to as A. Transduction. B. transformation. C. transposons. D. conjugation.

D. conjugation. Bacteria are asexual and divide by binary fission, meaning that they only receive genes from one parent cell and do not increase genetic diversity through reproduction. Instead, they increase genetic diversity through horizontal gene transfer, which refers to the transfer of genes between individual organisms (within a generation). The three methods of horizontal gene transfer are summarized below: Conjugation: Bacteria copy and directly transfer a special plasmid called the F plasmid (fertility factor) via a cytoplasmic bridge called a piliIf a bacteria contains the F plasmid, it is referred to as F+; if not, it is referred to as F-A plasmid is a circular piece of DNA that is independent from a bacterium's single circular chromosome Transformation: Bacteria take up extracellular DNA and incorporate it into their chromosome Bacteria are referred to as competent if they can perform transformationElectroporation is the process of using electrical impulses to force bacteria to become competent Transduction: Viruses transfer bacterial DNA between different bacterial hosts Transduction occurs when a bacteriophage enters the lysogenic cycle in its host and carries bacterial DNA along with its own genome upon re-entering the lytic cycle

What enzyme relieves supercoiling on the replicating strand during DNA replication? A. DNA helicase B. DNA polymerase C. Single strand binding proteins D. Telomerase E. Topoisomerase

E. Topoisomerase During the elongation step of DNA replication, helicase 'unzips' the wound DNA double helix by breaking the hydrogen bonds between complementary purines and pyrimidines. This creates tension ahead of the replication fork, referred to as DNA supercoiling. DNA supercoiling is defined as the over- or under-winding of a DNA strand, and is an expression of the strain on that strand. To relieve this tension, topoisomerase creates small nicks within the DNA double helix

Why do nerve cells differ from skin cells despite both cells having identical genomes?

Expression of different structural genes In a multicellular organism, all cells except gametes will have the same genome. Nevertheless, cells in different organs differentiate as a result of changes in gene expression. As cells differentiate, some genes turn on while others turn off. The homeotic genes play a key role in regulating the gene expression of different cells in different parts of the body. The result is cells with the same genome developing differently and expressing different protein products

DNA polymerase

Extends the complementary strand in the 5' → 3' direction

Steps of DNA transcription

Initiation - a promoter sequence next to the gene attracts RNA polymerase to transcribe the gene. Elongation - transcription bubble forms and RNA polymerase synthesizes mRNA in the 5' → 3' direction. Termination - a termination sequence (aka terminator) signals to RNA polymerase to stop transcribing the gene.

All of the following are methods of post-translational modification of polypeptides EXCEPT one. Which is the EXCEPTION? A. Glycosylation B. Protease activity C. Acetylation D. Removal of introns E. Methylation

Post-translational modifications are the changes made after translation ie. the changes made to a recently translated polypeptide. Removal of introns occurs after transcription and before translation, and therefore, removal of introns is a post-transcriptional modification. Removal of introns must happen in eukaryotic cells before the transcript is able to leave the nucleus (the site of transcription), and enter the cytoplasm (the site of translation). Below are some of the most common post-transcriptional modifications: - Addition of a 5' Guanine cap - 3' cleavage and attachment of poly(A) tail mRNA splicing of exons, intron excision

Which of the following is a DNA sequence that can change its position within a genome? A. Transposon B. Sigma factor C. Operon D. Inversion

Transposons are DNA sequences found in prokaryotes and eukaryotes that can move and integrate to different locations within a genome; as such, they can cause mutations if they are inserted into coding sequences.

expected daughter strand after DNA replication

example: 5' ACA TGG GAC 3' to 3' TGT ACC CTG 5' DNA replication is anti-parallel, which means new DNA is synthesized 5' to 3' in the opposite direction to the parent strand so 3' to 5' and DNA contains T (thymine), and RNA contains U (uracil).

If a scientist wanted to convert DNA into smaller fragments, which of the following enzymes would be used?

exonuclease

lac operon

inducible operon (it must be induced to become active) only be induced when glucose is not available as an energy source, so lactose must be used.

Which of the following best explains why eukaryotic DNA is generally longer than bacterial DNA?

introns The bacterial genome is significantly smaller than the eukaryotic genome. Due to this small genome, prokaryotic DNA is circular with a single origin of replication. Bacteria, in particular, lack histones that help condense DNA or introns. These introns are intervening (hence their name) regions of DNA that are removed from the pre-mRNA following transcription to form the mature mRNA. Exons are the regions that are expressed and thus not removed. Alternative splicing is the production of different combinations of introns and exons to allow a particular gene to express different variations of a particular protein product. Bacteria, in their simplicity, do not require this alternative splicing because all the different proteins can be contained in their circular genome. Thus, each bacterial gene encodes only one product. Eukaryotes, on the other hand, are more complex and have much larger chromosomes. These chromosomes would be significantly larger if not for alternative splicing capability that helps to make the large eukaryotic genome more compact. Nevertheless, the eukaryotic genome is still significantly larger than that of bacteria but not nearly as large as it would be thanks to alternative splicing.

when lactase is present, what will allolactase bind to?

lac repressor protein first way that the lac operon is controlled. This protein is constitutively expressed (always on). Thus, the lac repressor protein is always bound to the operator, blocking transcription. However, when lactose is present it is converted to allolactose. Allolactose binds directly to the REPRESSOR PROTEIN and INHIBITS it, allowing transcription to occur.

what are the three ways lac operon is controlled?

lac repressor protein, cAMP levels and catabolite activator protein (CAP)

palindromic sequence

palindromic sequence is one in which the nucleic acid sequence of a given strand and its complementary strand is the same when both are read in the 3'-5' direction or 5'-3' direction. sentence that is read the same in both directions such as the word RACECAR. example: 3'-GGATCC-5' 5'-CCTAGG-3' another example: 3'-CCAATTGG-5' 5'-GGTTAACC-3' NOT an example of a palindromic sequence: 3'-CATAC-5' 5'-GTATG-3' because the first strand and its complementary strand are not read the same when both are read from the 3'-5' or 5'-3' direction.

exonuclease

part of post-transcriptional modifications (polyadenylation) enzymes that cleave nucleotides/DNA one at a time from the end of a polynucleotide chain into SMALLER FRAGMENTS. This occurs via a hydrolyzing reaction that breaks phosphodiester bonds at either the 3' or 5' end.

how can bacteria use, replicate, and transfer circular pieces of extra-chromosomal DNA?

plasmids

R-factors (or R-plasmids)

plasmids that contain ANTIBIOTIC RESISTANCE OF BACTERIA. If it were observed that a colony of bacteria had an increased amount of R-factors, it would indicate that the bacteria have become ANTIBIOTIC-RESISTANT.

Single-strand binding proteins

prevents the separated strands from prematurely reattaching

The portion of an allele that codes for a protein product is found where in a gene? A. Promoter region B. Regulatory region C. Stop signal D. Intron region E. Reading frame

reading frame An allele is a particular variation of a particular gene resulting from some mutation within that gene (since alleles are variations of the same gene, they are on the same loci). These mutations can range from a single nucleotide to entire sequences. They can occur anywhere on the reading frame of a gene and thus affect the expression of this gene

cAMP and CAP

second level of lac operon regulation. cAMP levels are inversely related to glucose levels, so when glucose is low, cAMP is high. cAMP binds to catabolite activator protein (CAP), which then attaches near the lac operon promoter to help attract RNA polymerase, promoting transcription.

What is the Hayflick limit associated with?

telomere shortening The Hayflick limit pertains to the limited number of times a cell can undergo division until it has to stop and undergo apoptosis. This arises from the concept of telomere shortening, which is the shortening of DNA with each round of replication. This is due to the way that the lagging strand works in which DNA polymerase needs an RNA primer to start replicating, and an RNA primer needs a DNA strand to connect, always leaving an un-replicated region at the end of the strand.

CRISPR

used to induce deletions of specific sequences in the human genome the name comes from an antiviral mechanism used by bacteria to target and remove repeated palindromic sequences from invading pathogens. Scientists adapted this idea to humans by creating a technology to edit genomic regions of interest through additions or deletions of DNA sequences.

The broad use of antibiotics can result in...

vitamin deficiency

conjugation

when bacteria transfer DNA between each other via a cytoplasmic bridge called pili. pili also copy and transfer a special plasmid known as the F-plasmid

can bacteria transfer genes horizontally?

yes Bacteria are asexual organisms, which means that they do not reproduce by mating with another individual; rather, they divide by binary fission. Bacteria cannot increase genetic diversity via sexual reproduction or mating. However, bacteria are able to transfer genes horizontally (i.e. within a generation), which contributes to increased genetic diversity.