How does DNA copy itself?

Purpose: DNA copies itself to ensure that each new cell that is produced in gets the correct number of chromosomes and receives an EXACT copy of the DNA molecule.

Replication must occur before cell division.

• This is called DNA REPLICATION.

• The DNA molecule serves as its own pattern or template so as an exact copy can be made.

Watson and Crick• The model that Watson and Crick where

the nitrogen bases pair suggested a mechanism for DNA to replicate.

Messelson and Stahl• They proved that DNA is semiconservative

by attaching radioactive material to DNA. As the cell divided, they observed the new DNA in each cell and saw that it contained half of the old.

• Semiconservative: contains half of the old strand when DNA is replicated.

STEPS OF DNA REPLICATION

1. Helicase begin to unzip the double helix at many different places. The hydrogen bonds between the bases are broken. Occurs in two different directions.

2. Free floating in the cytoplasm nucleotides pair with the bases on the template. DNA polyermase bonds together the nucleotides. Small segments are bonded together.

3. Two identical strands of DNA result. The DNA will twist back together. DNA is called SEMICONSERVATIVE because it uses an old strand to make a new one.

This results in 2 new identical DNA molecules.

DNA Replication Video

http://www.youtube.com/watch?v=zdDkiRw1PdU&feature=player_embedded

DNA Replication Fork

Point where DNA is split apart to replicate. Forms a Y!

Role of Enzymes• 1. Helicase

unzips the two DNA strands.

• 2. DNA polymerase is the enzyme that joins individual nucleotides to produce a new strand of DNA. Proofreads DNA when finished!

DNA Replication in Prokaryotic Cells

• 1. Proteins binds to starting point.

• 2. Starts at a single point and proceeds in both directions.

Eukaryotic Replication

• Since eukaryotic cells are so much bigger, the replication will start at dozens to hundreds of different places on the DNA.

Transciption – Making of RNA• Transcription – process of copying DNA to

produce a complimentary strand of RNA. Transcription is making RNA from DNA

• Purpose = to make RNA that is complimentary to the DNA

Types of RNAThere are three (3) types RNA:1. Messenger RNA – (mRNA) carries messages from the DNA in the nucleus to the cytoplasm (ribosome).2. Transfer RNA – (tRNA) 20 different kinds which are only able to bond with one (1) specific type of amino acid. Carries the amino acids to mRNA.

Types of RNA

• 3. Ribosomal RNA – (rRNA) major component (part) of the ribosomes

RNA TRANSCIPTION

Transcription – the process by which DNA makes RNA.

Steps in RNA Transcription:1. A special enzyme tells DNA its time to

make RNA.

2. The enzyme tells the nucleotides to only bond with RNA nucleotides.

-The code letters for RNA are: A, C, G and U.

RNA TRANSCIPTION

3. Process occurs just like DNA replication

--When complete, only a single strand of RNA is formed UNLIKE DNA’s double strand.

--All three types of RNA are formed this way.

--All leave the nucleus and travel out into the cytoplasm.

Transcription Video

• http://www.bing.com/videos/search?q=transcription&view=detail&mid=EE2661D88067BDEFF3E7EE2661D88067BDEFF3E7&first=0&FORM=LKVR8&adlt=strict

RNA TRANSLATIONDefinition=Protein Synthesis: the formation of a protein using information coded on DNA and carried out by RNA in the assembly of amino acids.

Proteins are:a. Amino acids in chains – 20 kindsb. Made of 10’s or 100’s or 1000’s of amino acidsc. Must be arranged in a specific sequence for each

type of proteind. Function & type of protein is determined by amino

acid sequencee. DNA makes RNAf. RNA orders the amino acids

RNA TRANSLATION

Translation Process:1. mRNA goes to the ribosomes, tRNA goes to the cytoplasm.2. tRNA picks up amino acids& brings them to the ribosome.3. mRNA tells tRNA in which sequence to assemble the proteins.(mRNA is the template!)4. An amino acid chain is a protein.

RNA TRANSLATION

So WHAT??:

RNA makes amino acid chains

Proteins make cells

DNA makes RNA

Amino acid chains make proteins

Go to gslc.genetics.utah.edu/unitsTranslate & Transcribe a Protein and What is a Protein?

Translation

• Groups of 3 nucleotides on the mRNA code for each amino acid to build a protein.

• These groups of 3 are called: CODONS

• The tRNA brings the correct amino acid to the chain.

• You will build your own proteins tomorrow with the mRNA that you made yesterday!

We have been told that DNA is the blueprint for life, BUT what

does that mean?DNA holds the instructions that tell a cell how to construct amino acid chains. That is important because amino acid chains build proteins.

ANDProteins build cells

Steps to Protein Synthesis

• 1. DNA replication – make new DNA

• 2. Transcription – DNA message given to RNA

• 3. Translation – RNA is translated in amino acid chains(protein).

Prokaryotic - Protein synthesis

• Location – cytoplasm

• At the same time.

• Eukaryotic – Protein synthesis

SO, HOW DOES AN AMINO ACID CHAIN GET BUILT?

RNA stands for ribonucleic acidIt differs from DNA in three ways:1. RNA is single stranded.

2. The sugar in RNA is called ribose.3.Uracil is one of the bases in

RNA. There is NO thymine in RNA. This means A goes with U and G still goes with C.

Well, first we have to make something called RNA

DNA DNA ReplicationReplication• Replication: coping of DNA Replication: coping of DNA

• The DNA molecule produces The DNA molecule produces 2 2 IDENTICALIDENTICAL new complementary new complementary strands following the rules of strands following the rules of base pairing: base pairing:

A-T, G-CA-T, G-C

•Each strand of the Each strand of the original DNA serves as original DNA serves as a template for the new a template for the new strand strand

Semiconservative Model

• Replication is called semiconservation because one strand of DNA is used to as a template to make the new DNA.

Steps of DNASteps of DNA ReplicationReplication

1.DNA unzips and the hydrogen bonds between the nitrogen bases pulled apart. The base pairs are separated and are left exposed. This occurs in two different directions. This occurs along hundreds of different places at a time.

. Parental DNA

DNA Template

New DNA

Steps of Replication

2. Free-floating nucleotides are paired up to the free nucleotides. DNA polymerase bond the nucleotides together.

3.Two identical strands result. DNA polymerase checks for mistakes when complete.

DNA Replication

• DNA has 80 million base pairs in a chromosomes. DNA is copied at about 50 base pairs per second. This would take a month if replication did not occur at hundreds of different places at once.

1. Why is replication necessary?

2. Describe how replication works.

3. Use the complementary rule to create the complementary strand:

A---?G---?C---?T---?A---?G---?A---?G---?C---?A---?G---?T---?

Replication Quiz

1. Why is replication necessary?So both new cells will have the correct DNA2. When does replication occur?During interphase (S phase).3. Describe how replication works.Enzymes unzip DNA and complementary

nucleotides join each original strand.4. Use the complementary rule to

create the complementary strand:

A---TG---CC---GT---AA---TG---CA---TG---CC---GA---TG---CT---A

Replication Quiz

(1961)(1961) Watson & Crick proposed… Watson & Crick proposed…• ……DNA controlled cell function by DNA controlled cell function by

serving as a template for serving as a template for PROTEINPROTEIN structure.structure.

• 3 Nucleotides = a triplet or 3 Nucleotides = a triplet or CODONCODON(which code for a specific AMINO ACID)(which code for a specific AMINO ACID)

See p.303See p.303

• AMINO ACIDSAMINO ACIDS are the building blocks are the building blocks of proteins.of proteins.

DNA DNA TranscriptionTranscription

• DNA can “unzip” DNA can “unzip” itself and itself and RNARNA nucleotides match nucleotides match up to the DNA up to the DNA strand.strand.

• Both DNA & RNA Both DNA & RNA are formed from are formed from NUCLEOTIDESNUCLEOTIDES and and are called are called NUCLEICNUCLEIC acids.acids.

See p.301See p.301

DNA DNA TranslationTranslation

• The cell uses The cell uses information from information from “messenger” RNA “messenger” RNA to produce proteinsto produce proteins

See p.304-305See p.304-305

We will We will discuss details discuss details

of this on a of this on a later datelater date

Types of Nitrogen Base Pairs

DNA

1.Adenine w/ thymine

2.Cytosine w/ guanine

RNA

1.Uracil w/adenine

2.Cytosine w/guanine

CAUGCA

Transcription/Translation Quiz1. identify the amino acids coded for by

these codons:

UGGCAGUGC

ACCGUCACG

1. Why is transcription necessary?Transcription SIGNALS messenger RNA (mRNA) to carry the code for proteins out of the nucleus, to the ribosomes in the cytoplasm.

2. Describe transcription.

RNA polymerase binds to DNA, separates the strands, then uses one strand as a template to assemble MRNA.

3. Why is translation necessary?

Translation assures that the right amino acids are joined together by peptides to form the correct protein.

4. Describe translation.The cell uses information from MRNA to produce proteins.

5. What are the main differences between DNA and RNA.DNA has deoxyribose, RNA has ribose; DNA has 2 strands, RNA has one strand; DNA has thymine, RNA has uracil.

6. Using the chart on page 303, identify the amino acids coded for by these codons: UGGCAGUGCtryptophan-glutamine-cysteine

7. WHAT ORGANELLES ARE INVOLVED IN TRANSCRIPTION?

AMAZING DNA FACTS…AMAZING DNA FACTS…

• DNA from a single human DNA from a single human cell extends in a single cell extends in a single thread for almost 2 meters thread for almost 2 meters long!!!long!!!

• It contains information It contains information equal to some 600,000 equal to some 600,000 printed pages of 500 words printed pages of 500 words each!!! each!!! (a library of about 1,000 books)(a library of about 1,000 books)

LET’S REVIEW DNA…LET’S REVIEW DNA…LM p.44LM p.44

1.1. List the conclusions Griffith & Avery, List the conclusions Griffith & Avery, Hershey & Chase drew from their Hershey & Chase drew from their experiments.experiments.

2.2. Summarize the relationship between Summarize the relationship between genes & DNA.genes & DNA.

3.3. Describe the overall structure of the Describe the overall structure of the DNA molecule.DNA molecule.

4.4. What are the 4 kinds of bases?What are the 4 kinds of bases?

Reading Questions:

1. Are RNA Polymerase the same as DNA polymerase?

2. What role do “Promoters” have in transcription?

3.

SNORK ACTIVITY DIRECTIONS

• TURN TO THE “DNA, RNA & SNORKS” PAGE IN PACKET:

• READ THE 2 PARAGRAPHS ABOVE THE TABLE, AND THE 3RD PARAGRAPH BELOW THE TABLE.

AUA, UCG, GGC, UAU