DNA Replication Step By Step Process

DNA Replication Step By Step Process

We Are Going To Talk Basic Principles Or Essentials About DNA Replication So let’s Get Started. Before I Actually Get Into The Information I Just Want To Mention Something About DNA, DNA Encodes For Everything Regarding You If We’re Talking About A Bacteria And Codes Everything Regarding The Bacteria So Anything That Is Made Up Every Protein Even The Membranes Anything That’s Made You Know In Your Body Is Encoded By Genes And Genes Are Found On Your DNA. So It’s Important For Your Cells To Actually Replicate Or Make Copies Of Your DNA And So This Process Of Replication Is Very Important.


DNA Structure:-

The Sugar That Makes It Up Is Called Deoxyribose, So Here We Have Our Deoxyribose Sugar That’s What Makes Up The Backbone Right Here Of DNA. DNA Is Double-Stranded, So We See One Strand And Another Strand And In Addition To That Sugar, The Deoxyribose We Have Nucleotides Or Nitrogenous Bases. We Have Our Adenine We Have Our Thymine And We Have Our Guanine And Cytosine. So We Traditionally Know These As ATG And C In An Ideal World. Where There Is No Mutation A Traditionally Pairs With T And G Pairs With C. Adenine Already Paired Up With Thymine Now DNA Bases Can Either Be Purines, Purine Or Pyrimidine That’s A Long Word Right. Purine Include Adenine And Guanine So The Adenine And Guanine Are The Purines Right That Means. The Thymine And The Cytosine But I Mean That Cytosine Are The Parameters Remember A Pairs With T And G Pairs With C. The Bonds Found Between The Base Pairs If We Take A Look At The Adenine And Thymine We See That There Is One And Two Hydrogen Bonds Between.

The Adenine And Thymine When We Take A Look At The Guanine We Has One Two And Three. So The G C’s Have Three Bonds In Between And The A And T Have Two Bonds. So This Is DNA Another Thing I Want To Mention Is The Orientation You Will Have The Strands Members Double-Stranded They Will Be Anti Parallel What Does That Mean. You Will Have One End Starting With Three Prime And Ending In Five Prime And One Starting With Five Prime And Again 3 Prime. So They Are Almost Opposite Of Each Other Now I Want To Mention To You That 3 Prime End Has A Hydroxyl Group Sticking Out That Is Actually Very Important In The Aiding Of Making That Phosphodiester Bond.

We Find In The Backbone Of DNA, So On The 5 Prime End We Have A Phosphate Group That’s Sticking Out So When We Hear 3 To 5 Prime We’re Talking About The Location Of The Sugar And What’s Sticking Out. So On The 3 Prime End, That’s The Third Carbon Of The Deoxyribose And On The 3 Prime End, We Have That Hydroxyl Group Sticking Out  Whereas On The 5 Prime Ends Just On The Fifth Carbon Of The Sugar And We Have Our Phosphate Group. So There’s A Little Something About The DNA I Just To Look At A Better Structural Look At The DNA Remember DNA Is Composed Of A Nitrogenous Base.

So It Could Be A T G Or C We Have Our Sugar In DNA Is Deoxyribose And Then We Have Our Phosphate Group Which Is Present. All Right So Basically They Will Come Together To Make DNA. Is That DNA Not Only Is It Double-Stranded But It’s Also Found As A Helix.  So It’s Kind Of Like Coiling Around Right So It Is A Helix And It Has Major Grooves This Is A Minor Groove Here And Then It Has Major Grooves. So This Is A Major Groove That’s The Minor Groove So When Is Turning That’s The Way We See It Okay So This Is A Simplified Version Of Replication.


Key Points:-


  • Bacterial DNA Is Circular So We See That Here Now There’s One Chromosome In Bacteria Whereas Eukaryotes Have Multiple Like Humans Have 46.
  • Eukaryotic Have Multiple Origins Of Replication. Whereas Bacteria Since The Circular Only Has One Origin Of Replication.
  • DNA Stands For Deoxyribonucleic Acid So I Know You Learned That In School When You’re Younger.
  • What DNA Polymerase Does Is Actually Adding Another Key Player Which Are The Nucleotides So The Nucleotides Are Known As dNTPs Was Stand For Deoxynucleotide Triphosphates.
  • It Will Look At The Parent Strand And Based On Whatever Base Is Here Let’s See They Said Is Guanine, So This One Right Here So If That’s Guanine That Means It’s Going To Recruit The Complement. Which Should Cytosine Be With Is Here Which Is Actually Showing You That So It Serves As The Template Another Key Player.
  • I Do Want To Mention Is This Helicase, Helicase Is Really Important Because It Has To Be Able To Unwind And Unzip The DNA In Order For It To Get Replicated Because If It’s Closed It Cannot Do Anything. Those Are Some Of The Major Key Players, Of Course, This Is A Simplified Version And I Do Want To Mention Something Else To You Is That.


Bacteria Has One Now How Bacteria Replicate And How You Carry Us Replicate There May Be Some Differences. In The Machinery That Does It But The Process Is Very Similar To Start Out Remembering We Have Linear DNA So The Point Where Replication Starts Is Called Origin Of Replication. So We Know That Origin Of Replication Now That’s Where Replication Starts Now When Replication Proceeds In The Bacterial. It Will Go By Directionally So As Is Happening Bidirectionally. Until It Gets To An End Point Called A Terminus That Point That’s When It Stops And It Kind Of Looks Like This When It’s Done You Know Is That That Terminating Sequence And They Can Actually Be Clipped At That Point So I Just Wanted To Let You Know That The Origin Of Replication Is Where Starts The Replication. I Said Eukaryotes Has Multiple Origins Of Replication But Bacteria Has One.

DNA Replication:-

There Were Many Theories Circulating On How DNA Replicates Or How They Make A Copy Of Themselves First Start With The Ones. That Do Not Make Any Sense That We Know Now So There Was The Conservative Style Of Replication That Basically Said. What You Have After Around The Replication You Will Have One Whole DNA That’s All Old And Then You will Have One That’s Just Brand New That’s Known As Conservative Style Replication. Then We Have Two Dispersive Style That They’re Talking About Where Different Parts Of The DNA Can Be Found In The Growing Strands But What We Actually Do Know Is That DNA Replicates In Us And Other Biological Or Living Beings In The Form Of A Semi Conservative.

Replication What That Actually Means Is That During Replication You Know Because DNA Is Double-Stranded. I Will Talk About That One Strand Will Serve As The Template That’s Known As The Parent Strand And Then You’ll Have The Growing Strand Which Will Be The Complement To It And That Will Be Brand New So Semi Conservative Means Half Old Or Half Parent And Then Half New. Studies Research Has Shown Now That It Is Semi Conservative Style Of Replication So In Eukaryotes Like Human Or Plants The DNA Is Actually Linear So Linear Meaning Like You Know Our Chromosomes Look Like This Right This Actually Linear And Bacteria Is On The Other Hand Is Not Linear.


DNA Replication Step By Step Process:-


I Want To Introduce You To The Key Players That Play A Role In Replication So The First Thing I Want To Talk About Is Our Original DNA Template That Is The Parent Strand Of The DNA Because You Remember Here Some DNA And It Has To Be Opened Up. In Order For This To Happen So We Have Our DNA Template The Next Thing, I Want To Note Is A Very Important Key Player One Of The Major Key Players Is DNA Polymerase. So Based On If You Eukaryotic Versus Prokaryotic There Are Different Types Like I Know For Bacterium DNA Polymerase 3 Tends To Play The More Critical Role In Replication.



  • There Are Two Different Strands That We See In Replication So The Top Strand Is Known As The Leading Strand And The Bottom Strand Is Known As The Lagging Strand. And Because Of How The Orientation Of The Synthesis Is Or The Orientation Of The Parent Strand Is What Actually Drives Some Of The Things That We See In The Lagging Strand Is Not In The Leading Strand.

DNA Replication Step By Step Process

So This Diagram Right Here It Looks Like A Lot Of Stuff Going On So Let Me Just Explain This Is DNA In DNA Replication In Bacteria.


  • You Remember I Said That In Bacteria We Have That DNA Polymerase 3 All Right There It Is All Right So First Thing I Want To Say Is That The Leading Strand When It Gets Synthesized Is Synthesized Continuously And The Reason Why We See Because Of The Parent Strand. Is 3 To 5 Prime And The Synthesis Will Occur In 5 To 3 Prime Neurons Do You Remember That 3 Prime End Has That Hydroxyl Group That’s Needed For The DNA Polymerase To Help Make That Phosphodiester Bond In The Backbone.


  • There Typically Is A Primer That Will Start Off The Process And You Will Have Your DNA Polymerase That Will Slide Along The Leading Strand And Adding The Proper Bases And Remember There Is A Helicase That Will Be Ahead Of It That Will Unzip It And You’ll Also Have Proteins That Will Kind Of Stabilize The Before It Can Close Back On Itself.


  • This Is One Continuous By Human You To Look At This Lagging Strand, The Lagging Strand Has Something Called Okazaki Fragments. Okazaki Fragments Are Made Because There Is An Issue In The Parent Strand Direction.


  • The Parent Strand Is Going From Five To Three That Means If It Was To Synthesize It Would Be Synthesizing Kind Of Weird. So Here’s The Problem Ideally DNA Needs The Parent Strand To Be In That 3 Prime To 5 Prime Direction Okay Because If The Parent Is 3 To 5 Then It Will Be Synthesizing It’s New Strand 5 Prime To 3 Prime So Remember That 3 Prime End Had That Hydroxyl Group That’s Sticking Out The Hydroxyl Group Is Really Important For That DNA Polymerase To Work Now If You Take A Look At That Leading Strand.


  • The Leading Strand Is In That 3 Prime To 5 Prime When We Look At The Parent Strand It’s In The Proper Configuration But Remember It’s Anti Parallel So The Lagging Strand Is Not Actually Going To Start Out In The 3 Prime Direction It’s Starting Out In That 5 Prime Direction.


  • So That Causes A Problem It Would Not Be A Problem If The DNA Was Actually Unwounded All The Way Before Replication Started Right Because Then That 3 Prime End Would Be Here And That 3 Prime End Would Be Here And It Can Go Ahead And Synthesize You Know Synthesize Here Is A Leading Strand In That Direction And The Lagging Strand In This Direction But There Is An Issue Because The DNA Does Not Unzip Completely Before Replication Starts.


  • It Starts Replication As It Opens So Here Is The Product This Is How The Problem Is Actually Solved So Let’s Talk About How This Problem Has Actually Solved That Problem Is That The Cell Will Actually Produce These Little Work Enzymes In The Cell Were Produces Little Fragments Call RNA Primers.


  • RNA Primer Is Made By RNA Polyrimase That Will Make The Short Primers And What’s Actually At The End Of The Primers Is Three Prime Hydroxyl So We Have Those Hydroxyl Groups That Are Essentially Available Based On Those Primers Now Those Primers. That Polymerase Will Recognize That Primer.
  • We Will Start Adding The Bases Like How We Will See In The Leading Strand But Because We Have So Many Of Them Found In The Lagging Strand Each Of Those Primers With Bases Will Come Together As What’s Known As Okazaki Fragments. The Okazaki Fragments Are Primers Remember These Are RNA Primers That Are Temporary Substitutes Plus Nucleotide Bases.


  • Nucleotides And They Are Fragments They’re Short Fragments Our DNA Polymerase Will Recognize The Primer  3 Prime And I Start Adding Bases And It Will Stop When It Gets Close To Another Okazaki Fragment So We’ll Continue To Do That Now Once.


  • You Have These Okazaki Fragments We Can’t Leave Them Like That So There Will Be An Actual Of Another Type Of Polymerase That Will Come In Kind Of Kick-Off Those Primers And Fill It In With DNA And So We Won’t Have Any RNA Primers At That Point And DNA Ligase Will Come In And Seal Those Backbone Ends By Making The Bonds And Receive The DNA Ligase Working Here.


  • This Has Shown You DNA Polymerase 1 Is Kind Of Coming In And Filling In That Gap Whereas DNA Polymerase 3 Is The Main One So Just To Take Note The Leading Strand Is Continuous Because The Parent Strand Is 3 To 5 And It Will Have No Issues Making 5 To 3 Maybe Just Need 1 Primer To Start Off If That But When We Look At The Lagging Strand It Is The Parent Strand Is The Opposite And So Since You Cannot Wait To Unzip The Whole DNA The Problem Is Solved By RNA Primers Being Made By RNA Polymerase.


  • They Will Be Found All Throughout Polymerase Will Recognize It Synthesize The Different Fragments Called Okazaki Fragments And Then After We Have All These Fragments DNA Polymerase 1 Will Come In And Kind Of Replace That RNA Primer With The Proper DNA And Then DNA Ligase Will Come In And Seal Up The Rest So If You Take A Look At It The Leading Strand Looks Pretty Smooth Whereas The Lagging Strand Looked Like It’s Having A Pretty Hard Time But It Doesn’t Matter At The End Of The Day.


  • They All Work Now Just To Mention Here In Bacteria There Are Particular Types Of Topoisomerases That Are Present And Remember I Said Bacterial DNA Is Circular And It’s Not Found Looking Like A Circle In A Cell It’s Pretty Much Quailed We Call That Supercoiling. The Topoisomerases Kind Of Play A Role In Unwinding Or Winding Up To DNA Depending On What Type Of Topoisomerase Is Present.


  • I Just Want To Mention To You There Are A Lot Of Bases That DNA Polymerase Has To Add In A Short Period Of Time Thing That Happens Is That There Can Be Accidents Where Bases The Wrong Base Can Accidentally Be Added If That Happens It May Be Picked Up And It May Be Corrected And How That Happens Is That DNA Polymerase Actually Has A Proofreading Function So As The DNA Is Added.


  • There’s A Portion Of DNA Polymerase That Will Double Check And Make Sure It’s Correct If It’s Not Correct It Can Remove The Wrong Base And Place It With The Right One I Actually Like That Because If That Didn’t Happen There Would Be So Many More Issues Going On A Lot More Tumors And Cancers And Things That Are Arising So DNA Polymerase Does Have A Proofreading Function There’s One Part Of It That Plays A Role In That Growing Strand. There’s A Proofreading Part Portion To It And There’s A Primer Removal Portion Or If It Needs To Correct A Problem It Can Do.