Chapter 12-2Chapter 12-2

Chromosomes and Chromosomes and DNA ReplicationDNA Replication

Remember?Remember?

• The DNA double helix is coiled The DNA double helix is coiled up to make chromosomes.up to make chromosomes.

• Chromosomes contain all the Chromosomes contain all the genetic information that makes genetic information that makes an organism what it is.an organism what it is.

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How long is DNA?The chromosome of the bacteria The chromosome of the bacteria E. coli, which lives in your large E. coli, which lives in your large intestine, has 4,639,221 base intestine, has 4,639,221 base pairs.pairs.

That’s over 4.6 million of these!

This means that if you counted 1

base pair per second, it would take

you 54 days to count them

all.

How is DNA organized into How is DNA organized into chromosomes?chromosomes?

??

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Before a cell divides, it must copy its DNA.

Remem

b

Remem

b

er?

er?

So how is DNA copied So how is DNA copied (replicated)?(replicated)?

How is DNA copied (replicated)?• The complementary strands of the The complementary strands of the

DNA double helix allow it to be DNA double helix allow it to be copied.copied.

• Each strand can be used to make Each strand can be used to make another strand because of the rules another strand because of the rules of of base pairingbase pairing..

• Each strand of the double helix Each strand of the double helix serves as a template, or model for serves as a template, or model for the new strand.the new strand.

DNA ReplicationDNA Replication

replication

cbp-4122

Draw some form of this on the DNAStructure tab of your flip book.

DNA Replication activity:DNA Replication activity:

www.phschool.com, find online textbook. Go to page 298.

Click on

12-3: RNA and Protein Synthesis

We know that DNA is the We know that DNA is the genetic code and that it can genetic code and that it can copy itself. But how does the copy itself. But how does the gene work?gene work?

California content standards:California content standards: Genetics 4 a,b,e; 5 a,bGenetics 4 a,b,e; 5 a,b

Dude, we’re seriously low on

burgers!!!!!

NUCLEUS

CYTOPLASM

Burger Factory

Messenger

DNADNA

RibosomeRibosome

mRNAmRNA

DNA message must first be copied to RNARNA

• RNA sugar is RNA sugar is RRibose (vs. deoxyribose)ibose (vs. deoxyribose)• RNA usually single-stranded (not double)RNA usually single-stranded (not double)• RNA contains RNA contains UracilUracil in place of in place of ThymineThymine

RNA is similar to DNA, but has RNA is similar to DNA, but has these differences:these differences:

12-312-3DNA: A T C C G A A T C GRNA: U A G G C U U A G C

•1) Messenger RNA (mRNA)1) Messenger RNA (mRNA)•2) Ribosomal RNA (rRNA)2) Ribosomal RNA (rRNA)•3) Transfer RNA (tRNA)3) Transfer RNA (tRNA)

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There are 3 types of RNA:

These are all involved in makingThese are all involved in makingPROTEINSPROTEINS

1. mRNA1. mRNA carries carries a copy of DNA a copy of DNA instructions to instructions to the rest of the the rest of the cell (a cell (a “messenger”)“messenger”)

2. 2. rRNArRNA combined with combined with proteinprotein makes a makes a ribosomeribosome. . This is where proteins are This is where proteins are assembled.assembled.

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Located in the

cytoplasm

3. 3. tRNAtRNA transfers transfers amino acids to the amino acids to the ribosome, based ribosome, based on the code in on the code in mRNA.mRNA.

Bases

(just like

DNA)

Amino acid attaches here

Transfer Transfer RNARNA

Protein Protein SynthesisSynthesis

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Remember: the genetic code is instructions for producing _________ ?Proteins

There are 2 steps in Protein Synthesis: 1.

2.

1. Transcription (DNA 1. Transcription (DNA strand transcribed)strand transcribed)

2. 2. Translation:Translation:Polypeptide Polypeptide assembled.assembled.

Step 1: Step 1: transtransccriptionription• DNA code copied to messenger DNA code copied to messenger

RNA. mRNA bases are RNA. mRNA bases are complimentarycomplimentary to the DNA strand. to the DNA strand.

DNA: T C G C A T A

RNA:

12-312-3Remember the base-pairing rules?

Checkpoint

1. The genetic code is a set of instructions 1. The genetic code is a set of instructions or a “recipe” for the production of or a “recipe” for the production of _________._________.

2. The first step in protein synthesis is ?2. The first step in protein synthesis is ?

3. Which type of RNA is the DNA message 3. Which type of RNA is the DNA message copied to in the nucleus?copied to in the nucleus?

Each group of 3 bases on Each group of 3 bases on mRNAmRNA is a is a code “word.” Each “word” is called code “word.” Each “word” is called a a codoncodon and specifies an amino acid and specifies an amino acid to be added to a polypeptide. to be added to a polypeptide.

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DNADNA strand strand::TT AA CC CC CC AA AA TT CC

Complementary Complementary mRNAmRNA strand: strand:AA UU GG GG GG UU UU AA GG

CODONCODON CODONCODON CODONCODON

methionine(start) Glycine (stop)

Polypeptide

- -

AminoAcids

How do you tell what amino How do you tell what amino acid a codon specifies?acid a codon specifies?

You use a You use a codon tablecodon table::

1st

3rd

2nd

Step 2: Step 2: transtransllationation• mRNA strand moves through nuclear pore into mRNA strand moves through nuclear pore into

cytoplasm.cytoplasm.

• Here it joins up with the 2 other kinds of RNA: Here it joins up with the 2 other kinds of RNA: rRNArRNA, t, tRNARNA

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Transfer RNA (tRNA)Transfer RNA (tRNA)

• Holds amino acid to be added Holds amino acid to be added to growing polypeptide chain.to growing polypeptide chain.

• Each tRNA will pick up only 1 Each tRNA will pick up only 1 kind of amino acid.kind of amino acid.

• Anticodon loop is on bottom.Anticodon loop is on bottom.

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Transfer Transfer RNARNA

UU CCAA

Approximately Approximately 80 nucleotides 80 nucleotides long.long.

This anticodon is complementary to codon on mRNA

Amino acidattachment site

Translation

Translation

Putit all

together

Recap

Gene 1Gene 1 Gene 2Gene 2

polypeptide 1polypeptide 1 polypeptide 2polypeptide 2

26-3

• What is the DNA double helix composed of?

• What bases pair together?

• What is transcribed from the DNA strand?

• Where does this occur?

• What are the 3-base triplets on mRNA called?

• What is translation and where does it occur?

• What are the 3-base codes on tRNA called?

• What is the final outcome of all this?