GENE

EXPRESSION

What is DNA Replication?• DNA Replication – the process of

creating copies of DNA molecules

Why is DNA Repliction SEMI CONSERVATIVE?– DNA Replication is SEMI-

CONSERVATIVE (each strand of the original DNA molecule serves as a template for the two new DNA molecules)

• Thymine and cytosine each have one ringThymine and cytosine each have one ring

C

C

C

C

N

N

OO

OO

thyminethymine

C

C

C

C

C

N

N

OO

OO

thyminethymine

C

C

C

C

N

N

OO

OO

thyminethymine

C

C

C

C

C

N

N

OO

N

cytosinecytosine

C

C

C

C

N

N

OO

N

cytosinecytosine

One ring

• Adenine and guanine each have two ringsAdenine and guanine each have two rings

C

C

C

C

N

N

OO

N

GuanineGuanine N

N

C

C

C

C

C

N

N

OO

N

GuanineGuanine

C

C

C

C

N

N

OO

N

C

C

C

C

N

N

OO

N

GuanineGuanine N

N

C

C

C

C

C

N

N

N

AdenineAdenine N

N

C

C

C

C

C

N

N

N

AdenineAdenine

C

C

C

C

N

N

N

C

C

C

C

N

N

N

AdenineAdenine N

N

C

Two rings

Hydrogen Bonds

• When making hydrogen bonds, a double ring always pairs with a single ring

• A – T

• C – G

C

C

CC

N

N

N

N

N

C

C

C

C

C

N

N

OO

OO

C

C

C

CC

N

N

N

N

N

C

C

C

CC

N

N

N

C

C

CC

N

N

N

C

C

CC

N

N

N

N

N

C

C

C

C

C

N

N

OO

OO

C

C

C

C

C

N

N

OO

OO

C

DNA Replication: Simplified

DNA Replication = 3 steps

What are the 3 steps of DNA Replication?

DNA Replication = 3 steps

1. Unzip DNA

2. Add free nucleotides

3. Re-zip new strands to old strands

Enzymes Play an Important Role!

• Enzyme #1 = helicase

(unwinds DNA)

Many enzymes help DNA replicateEnzymes are proteins

Many enzymes help DNA replicateEnzymes are proteins

• Enzyme #2 = DNA Polymerase

(add new nucleotides, “proofreads”

for mistakes

Enzymes Play an Important Role!

So...exactly HOW do we use our DNA?• Our DNA sequences serve as a code!

• ACTGGGACTACCATTGA

• We take this information and make RNA molecules, which help us to make proteins!

DNA Review:Try to fill in the blanks:

1. A nucleotide is made of three parts:

______________ , __________________,

and one of the _______ pairs.

2. The nucleotides are combined together to

create a __________ acid, and ______ is

an example of this.

Review:

1. A nucleotide is made of three parts:

DEOXYRIBOSE SUGAR__ ,

_PHOSPHATE_, and one of the __BASE _

pairs.

2. The nucleotides are combined together to

create a _NUCLEIC_ acid, and _DNA_ is

an example of this.

More about Nucleic Acids!

• We’ve already learned about one important nucleic acid, DNA. Today, we’ll explore the second nucleic acid…

• RNA!!

RNA NOTES

How is RNA different from DNA?

Three differences from DNA:

1. RNA = one strand (DNA = two strands)

2. RNA has the sugar ribose (DNA has the sugar deoxyribose)

3. RNA uses uracil [U] instead of thymine (DNA = A, T, G, C RNA = A, U, G, C )

DNA vs. RNA

Deoxyribose Sugar Ribose Sugar

Double Stranded Single Stranded

(usually) (usually)

THYMINE base URACIL base

1 type of DNA 3 types of RNA

(mRNA, rRNA, tRNA)

Examples of Nucleic Acids

Made of Nucleotides

Code for Information

DNA

RNA

What are the 3 types of RNA?3 types of RNA:

• Messenger RNA (mRNA) carries the genetic message

• Transfer RNA (tRNA) transfers amino acids

• Ribosomal RNA (rRNA) makes ribosomes

D N A

Transcription

What is Transcription?transcribe = “to copy”

The genetic code on DNA is copied to RNA in the nucleus

Why does it happen in the nucleus?Original DNA cannot pass through the nuclear membrane, so a smaller copy is made and transported

• Where in the cell does transcription happen?• The nucleus!

• Why does it happen in the nucleus?• Original DNA cannot pass through the nuclear

membrane, so a smaller copy is made and transported

How does Transcription happen?

1. RNA polymerase unwinds DNA

2. RNA polymerase adds RNA nucleotides

(A U, G C)

3. mRNA is formed! DNA reforms a double helix

Transcription recap…

• RNA polymerase makes RNA using DNA sequence

• RNA leaves the nucleus for the cytoplasm

TranslationWhere does it go from there?

Into the great beyond?

To a ribosome! (Floating in cytoplasm)

At this point you only knew ribosome's as little dots in the cell… now you will learn their big purpose!

Turning RNA into the proteins that make up your hair, skin, muscles, nails etc!

What is translation?

• Ribosomes translate mRNA into an amino acid sequence

• Amino acids form proteins

What is a Codon?Codons = 3 nucleotides in a row

Ribosome recognizes a codon on mRNA and matches to the aniticodon on tRNA

A C G

anticodon

amino acid

How are codons used?

How do tRNA and anticodons work together?

Transfer RNA transfers amino acids from the cytoplasm to a ribosome

Anticodon = 3 nucleotides on one end of a tRNA

Anticodons base pair with complementary bases on mRNA

A C G

anticodon

amino acid

Codons

Codon triplets code for 1 of 20 amino acids

1 “start” codon 3 “stop” codons

Codons

Steps of Translation

1. mRNA attaches to ribosome

mRNA

Steps of Translation

2. tRNAs add amino acids based on how anticodons match to mRNA

mRNA

Steps of Translation

mRNA

2. tRNAs add amino acids based on how anticodons match to mRNA

Steps of Translation

mRNA

2. tRNAs add amino acids based on how anticodons match to mRNA

Steps of Translation

mRNA

2. tRNAs add amino acids based on how anticodons match to mRNA

Steps of Translation

mRNA

2. tRNAs add amino acids based on how anticodons match to mRNA

Steps of Translation

mRNA

2. tRNAs add amino acids based on how anticodons match to mRNA

Steps of Translation

mRNA

2. tRNAs add amino acids based on how anticodons match to mRNA

Steps of Translation

mRNA

2. tRNAs add amino acids based on how anticodons match to mRNA

Steps of Translation

mRNA

2. tRNAs add amino acids based on how anticodons match to mRNA

Steps of Translation

2. tRNAs add amino acids based on how anticodons match to mRNA

Steps of Translation

3. Protein is released from ribosomes!

Protein chain

Stop codon

Steps of Translation

Protein chain

3. Protein is released from ribosomes!

What process turns DNA into RNA?

•Transcription!!

What process turns RNA into PROTEIN?

•Translation!!

What do amino acids build?

•Protein!!

Summary

DNA

RNA

PROTEIN

(Transcription)

(Translation)

Gene Expression Practice1.DNA sequence: AAC TGA CTG ATT GCA TGC

• What is the complementary DNA sequence?

• What is the complementary RNA sequence?

• What are the amino acids for this sequence?

2.DNA sequence: TAG CAT TGG GCA TCA CGA

• What is the complementary DNA sequence?

• What is the complementary RNA sequence?

• What are the amino acids for this sequence?

TTG ACT GAC TAA CGT ACG

UUG ACU GAC UAA CGU ACG

ATC GTA ACC CGT AGT GCT

AUC GUA ACC CGU AGU GCU

Determine the amino acids for this strand of mRNA:AUG GCA AGU UCU UGA

EXIT QUIZ

Met – Ala – Ser – Ser – STOP(Use genetic code table on page 186-Turtle or p. 526)

Determine the amino acids for this strand of mRNA:UGU AGA GAU CUC UAA

Practice

Cys – Arg – Asp – Leu – STOP(Use genetic code table on page 186-Turtle or p. 526)

Big PictureGene Expression Short Essay

• Take one of the gene expression pictures and staple or tape it to a piece of paper (you may also choose to draw this out).

• Explain in your own words how DNA is used to make proteins including a brief description of DNA replication, transcription, and translation.