DNA Replication Practice

DNA REPLICATION PRACTICE

What I will be learning......

I will be learning about the structure of DNA

Why I will be learning this.....

Every organism on Earth is made with DNA, the same DNA that makes me.  All life is related by this one thing.

How I will know I learned this...

I will be able to correctly identify base pairs and their bonds, the enzymes of replication, and how DNA is packaged as a chromosome.

First watch this video from "Learn Genetics Utah": What are DNA and Genes?

Additional Reading resources are in your online book:   3.1 DNA, RNA, and Protiens pg 135-144

Additional Video resources: Amoeba Sisters DNA Replication

DNA replication is copying DNA as needed for mitosis.  In order to copy DNA, an enzyme Helicase, has to unzip the DNA by cutting the hydrogen bonds between bases.  Another enzyme, DNA Polymerase, will then attach to each DNA strand and start building the second side of the DNA called the complimentary strand. DNA Ligase helps bond the backbone phosphates and sugars together as the strand is begin built.  

• DNA is labeled by a 5’ and 3’ end.  DNA polymerase will only work from a 5’ to 3’ direction. 
  • One strand is 5’ and DNA polymerase can just build a continuous strand.  This is called the leading strand. 
  • The other strand starts with a 3’ so DNA has to build the strand is fragments called Okazaki fragments.  This is the lagging strand. 
    • An enzyme then has to join these fragments together to make a complete DNA copy. 

Each finished DNA strand is then made up of one old half of DNA and one new half of DNA.  The entire DNA molecule is called a chromosome, and it is very long, in fact over 6 feet long.  It is about 2 nm wide.  A human hair is about 80,000 nm wide.  If all the DNA in your several trillion cells were laid end to end, it would reach to the sun and back 600 times.  Humans have 46 chromosomes in all their "somatic" cells ( anything that isnt a sex cell). All that DNA has to be wound up so that it fits inside the nucleus of your cells.  You could fit 10,000 nuclei on the head of a pin. That is a lot of DNA to fit inside a nucleus. It is packaged as individual chromosomes, and wound around histones so it doesn't get tangled or damaged,  and can be copied and replicated when it is needed.  DNA has lots of mechanisms to get proof read when it's being copied, and repaired if a mistake was made. Sometimes mistakes can be made, though, and they are called mutations.  We will learn more about those later. 

Remember:  A binds to T and C binds to G

On the following questions, write the complimentary strand for the DNA strand given.  

For example:

I give you the strand   

• AGTCCAGATATTCCGA

You respond withe the complimentary strand

• TCAGGTCTATAAGGCT  (A turns into a T, G turns into a C and visa versa)