Let’s review:  DNA looks like a spiral staircase.  DNA is made of nucleotides which have two parts:  Sugar-phosphate backbone  Base  The handrails (sugar phosphate backbone) give DNA it’s shape.  The stairs (bases) store the genetic code

Let’s review:  DNA is instructions for building your body. They hold your genetic code (your genes). GENES are sections of DNA that code for a certain trait.  When DNA is wound tightly into a ball it is called a CHROMOSOME. Humans have 23 PAIRS of chromosomes

What is Replication?  DNA replication is the process of copying DNA  DNA Replication allows cells to grow and reproduce (make new cells).  In humans and animals, it is the first step of mitosis, which occurs when cells in your body grow (like your muscles).  It is also very important for meiosis, which is the first step of sexual reproduction.  DNA Replication allows a cell to pass down its genetic information to the next generation.  The cell needs to make copies of its DNA so it can give some to it’s “children” and still have some left for itself!

 Doubles the amount of genetic material so that when a cell splits, both will have the same amount of DNA as the original did.  In bacteria, DNA replication is how cells reproduce. In human beings and other animals, other steps are required. Why does DNA Replication occur?

How does REPLICATION work?

There are 3 main steps to DNA replication:  Step 1: Bonds break between BASES. The DNA molecule begins to unzip and the two individual strands unwind.  Step 2: Two strands of DNA serve as templates for new DNA. Free nucleotides and bases begin to attach themselves to the open strand of DNA.  Step 3: The new strand of DNA is “proofread” for errors. There are two new molecules of DNA which are exact copies of each other. Each DNA molecule has one old strand and one new strand.

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Let’s Replicate!

What is RNA?!  RNA is like a photocopy of the DNA.  The DNA has instructions for everything about you. When your cells construct new parts of you, they only need a part of your DNA.  So, your cells make a photocopy of the DNA to use to create new parts of you (protein).  This is the RNA! We call it mRNA for MESSENGER RNA!

What is RNA?  RNA is just like DNA, except that it is only one strand, instead of two (not a spiral staircase). Also, it is not nearly as long.  The other difference is that RNA replaces all of the THYMINE with URACIL.  So, C still pairs with G.  Cytosine with Gaunine  But now, A pairs with U.  Adenine with Uracil

Transcription  mRNA is created through the process of transcription.  Step 1: Just like DNA replication, transcription occurs by splitting the DNA apart. However, in transcription it is only temporary.  Step 2: The mRNA strand pairs up with one strand of DNA and bases come together.  The only difference is mRNA pairs A with U (it still pairs T with A).  Step 3: The DNA molecule comes back together and the mRNA heads off to build proteins.

Transcription  Transcription creates a photocopy (mRNA) of the instructions (DNA) that can be used to create proteins  mRNA is a single strand, rather than a double helix.  C  G, G  C, T  A, A  U  Let’s try it:  DNA: GCTGAATGCCGTA  mRNA: CGACUUACGGCAU  DNA: ATGCCGTATAAGC  mRNA: UACGGCAUATTCG Yvg&NR=1

Let’s Transcribe

Replication vs. Transcription  Replication permanently splits DNA apart to make 2 exact copies of new DNA.  Used for cells to grow (make new cells) and for reproduction  The final product is 2 new strands of DNA that are passed on to new cells or a new organism.  Transcription only temporarily splits DNA to make MESSENGER RNA.  Used as a photocopy of the DNA to build proteins.  The final product is a 1-strand section of mRNA that is not passed on to new cells or a new organism. In fact, mRNA is only used once.

Exit Slip  What are some differences between DNA and RNA?  What is mRNA used for?  What are some differences between replication and transcription?