Replication, Transcription and Translation

Honors BiologyPowerpoint #2 – Chapter 12

Warm Up: Base Pairing

1.

2.

A C C T G A

G C T AG A G

What is the DNA ‘backbone’ made of?

Phosphate

and Sugar

DNA Replication

Hydrogen bonds

Nucleotide

Sugar-phosphate backbone

Key

Adenine (A)

Thymine (T)

Cytosine (C)

Guanine (G)

What is DNA replication?

Making a copy of DNA

Why is DNA replication important for cells and

multicellular organisms? Replication allows cells to divide

Forming cells that are genetically identical to the original

When does DNA Replication occur?

After the cell grows big enough to divide, during interphase, the “S” phase

DNA Replication

Growth

Growth

Replication fork

DNA polymerase

New strand

Original strand DNA

polymerase

Nitrogenous bases

Replication fork

Original strand

New strand

Important Enzyme #1

HelicaseUnwinds DNA at the replication fork.

Important Enzyme #2

DNA PolymerasePrincipal enzyme in DNA replication; adds nucleotides to growing strand of DNA and proofreads new strand of DNA

Steps in DNA Replication

1. Helicase enzyme breaks the hydrogen bonds between base pairs. This unzips the double helix at a position called the replication fork.

2. There is an abundant supply of nucleotides in the nucleus for the formation of the new polynucleotides.

3. Nucleotides base pair to the bases in the original strands with hydrogen bonds.

4. DNA polymerase joins together the nucleotides together with strong covalent bonds to form a new complementary polynucleotide strand.

5. The double strand reforms a double helix.

6. Two copies of the DNA molecule form behind the replication fork. These are the new daughter chromosomes.

Drawings of the steps in DNA Replication

DNA Polymerase

Helicase

Some Important DNA Facts

A strand of DNA has 2 ends, the 5’ (5-prime) and 3’ (3-prime) ends.

DNA is ALWAYS copied from 5’ to 3’

Some Important DNA Facts

There are multiple ‘bubbles’ of DNA replicated at the same time

What is ‘semi-conservative’ replication?

In the new DNA created, one strand is from the original, and one is a new one.

Semi = part ofConserve = save

Why is ‘semi-conservative’ important?

The DNA is copied EXACTLY generation to generation

RNAWhere is DNA stored? ______________________

What organelle makes proteins? ______________________

Where are proteins made? ______________________

Nucleus

Ribosomes

Cytoplasm

What problem might this pose?

DNA can not take directions for making proteins to the ribosomes.

How does RNA solve this problem?RNA is a disposable copy of DNA that can leave the nucleus

B. RNA’s structure is very similar to the structure of DNA except for 3 major differences:

1. RNA has ribose sugar instead of deoxyribose

Nitrogen Base

2. RNA is single-stranded

3. RNA has uracil (U) instead of thymine (T)

DNA: AGTCCTTTAGT

RNA: AGUCCUUUAGU

There are three main types of RNA:

1. Ribosomal RNA (rRNA)

rRNA is found in ribosomes, and

creates the active site for protein

formation

2. Transfer RNA (tRNA)

tRNA contains the anticodon, and

brings amino acids to create proteins

3. Messenger RNA (mRNA)

mRNA provides the template for making proteins

III. Transcription

A. Transcription: Producing RNA by copying part of the DNA’s nucleotide sequence

RNADNA

RNApolymerase

Adenine (DNA and RNA)Cystosine (DNA and RNA)Guanine(DNA and RNA)Thymine (DNA only)Uracil (RNA only)

B. Describe the process of transcription using drawings.

1. RNA Polymerase rips open the DNA double helix

2. RNA polymerase grabs bases and lines them up with the original DNA strand

3. Half of the DNA is copied into a strand of mRNA, then the DNA strand closes, hydrogen bonds reform

Transcription

C. How does RNA polymerase know where

to start?

Starts when it finds a

“promoter” (specific base

sequence)Found near the

beginning of a gene

sequence

D. Describe the process of RNA editing

RNA editing is a process that occurs in the nucleus.

It removes introns “intervening sequences” and leaves mRNA with only the exons “expressed sequences.”

After editing a cap and tail are attached and the mRNA is ready to enter into the cytoplasm.

IV. Translation

A. Proteins are long chains of amino acids.

B. Codon: 3 consecutive nucleotides that “code” for a specific amino acid.

What is the universal “start” codon:

AUG What are the three “stop” codons?

UGA, UAA, UAG

The Genetic Code

The Genetic Code

C. Use the genetic code below to translate the following mRNA sequences:

1. mRNA: A U G U A U C G G G C A U U U U A A

2. mRNA:U C C A U G G A A G U G A U U C C A U A A

3. mRNA:C C A U G U G U C C C C A A U G A A A A

C. Use the genetic code below to translate the following mRNA sequences:

1. mRNA: A U G U A U C G G G C A U U U U A A

2. mRNA:U C C A U G G A A G U G A U U C C A U A

A

3. mRNA:C C A U G U G U C C C C A A U G A A A A

Methionine (START), Tyrosine, Arginine, Alanine, Phenylaline, STOP.

Serine, Methionine, Glutamic Acid, Valine, Isoleucine, Proline, STOP

Methionine, Cysteine, Proline, Glutamine, STOP, Lysine

D. Translation:

The decoding of RNA into a polypeptide chain (protein)

E. The Central Dogma of Biology is:

DNA RNA protein

Where does the first

step take place? Nucleus

Where does the second step take place? Cytoplasm

F. What is the job of tRNA during translation? Bringing amino acids to the ribosomes and match them up with the correct base on mRNA.

What is an anticodon? The three bases on a tRNA that match with the mRNA codons.

G. What is the role of the ribosome during translation? It is the site of protein assembly

H. 1) mRNA is transcribed in the nucleus then travels to the cytoplasm

Cytoplasm

Nucleus

mRNA

2) Ribosome grabs mRNA. tRNA brings amino acids to the ribosome

Cytoplasm

mRNA Start codon

Ribosome

Methionine

Phenylalanine

tRNALysine (amino acid)

3) tRNA matches with complimentary mRNA.

Ribosome makes peptide bond between amino acids, and breaks the bond between tRNA and amino acid.

mRNARibosome

Translation direction

LysinetRNA

Peptide bond

4) Peptide chain continues to grow until ribosome reaches a stop codon

Protein is complete.

tRNA

Ribosome

Growing polypeptide chain

mRNAStop codon