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DNA replication

Why is DNA double-stranded?

Isn’t that a waste of time and energy to have the entire gene written twice? It It Would Would Like Like Be Be Writing Writing Each Each Word Word Twice Twice 😉

Seems silly, right? Yet cells do this because it allows the cell to quickly and exactly make copies (duplicates!)

Video on base-pairing


Videos on DNA replication



DNA Replication


Here is more detail:

DNA replication

Here is the same phenomenon, but with a bit more detail


Conservation of the genetic code

This process lets any cell make a new cell, with (almost) exact copies  of it’s DNA. I say “almost” because mistakes may occur. If the resulting cell survives, then it has changed DNA, and we call this a mutation.

DNA transcription

Making an RNA copy of the DNA original.

DNA is the “original”, kept safe in the nucleus.

RNA is the “copy”, which leaves the nucleus and goes into the cytoplasm

RNA then goes to a ribosome, where it is used to make a protein.

{ http://additionalbio.blogspot.com/2013/10/protein-synthesis.html }

Protein synthesis

Difference between DNA and RNA?

Instead of being made of C, G, A and T, we have C, G A and U. U is Uracil, a base only found in RNA.

DNA is double-helical, while RNA is single helical.


How does the cell copy DNA into an RNA copy?

1. DNA gene unzips

2. RNA molecules float in.

3. RNA molecules join up with their complimentary DNA.

4. The RNA molecules now peel off, and leave the nucleus.

Note that it’s actually called messenger RNA.

{ http://peer.tamu.edu/curriculum_modules/Cell_Biology/module_4/whatweknow3.htm }
{ http://leavingbio.net/HEREDITY-ORDINARY%20LEVEL.htm }



This process is mind-bogglingly fast.  Here is a video showing, with detail, the amazing speed at which this takes place:


DNA translation

Sending RNA to a ribosome, to build a protein.

Here is a video showing, with detail, the amazing speed at which this takes place:



DNA Replication details:

Replication of DNA

In order to be replicated, DNA must first unwind its characteristic double helix structure to form what is called the replication bubble. The resulting single-stranded DNA (ssDNA) serves as the template for replication, which occurs at the two edges of the bubble termed the replication fork.

The two strands of ssDNA are replicated simultaneously but with slightly different methods. The leading strand seen on the top in these animations is replicated continuously by the protein calledDNA polymerase (orange). DNA polymerase matches the base pair on the template with its corresponding nucleotide to reform the double-stranded DNA with its characteristic double helix shape.

The lagging strand seen on the bottom is replicated as the DNA unwinds in pieces using short segments of RNA (red) to guide DNA polymerase. While not shown in this animation, a different protein swaps the RNA segments for DNA and then the pieces are joined together by DNA ligase.


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