Unit 5: DNA and Protein Synthesis

Part 1: What is DNA? and History of DNA

Objectives: • Identify what DNA is

• Trace the history of DNA and its discovery

What is DNA?• DNA is an acronym

that stands for deoxyribonucleic acid.

• It indirectly controls all the functions of your body by telling ribosomes how to make proteins.

The history…• In the early 1950’s

scientists thought that proteins were the genetic material.

• In 1952 Alfred Hershey and Martha Chase performed an experiment with viruses that proved that DNA was the genetic material.

More history…• In 1953, James Watson

and Francis Crick accurately described the structure of DNA.

• They could never have done this without the help of Rosalind Franklin but, because she was a woman, she was denied credit for decades.

Summary Questions!

1. What does DNA stand for?

2. What 2 people were credited with the discovery of DNA?

3. Who was also involved but received no credit?

Part 2: DNA Structure

Objectives:

•Describe the structure of DNA

•Identify the parts of a nucleotide

•Describe base pairing

DNA structure

• DNA is a double helical structure. (double helix)

• It looks like a twisted ladder.

A close-up…

DNA is Made of Nucleotides

• Nucleotides are molecules that make up the structure of DNA.

1. A simple sugar (in DNA it’s called deoxyribose)

2. A phosphate group

3. A nitrogenous base pair (AT or CG)

How do the pieces fit together?• The sugar and

phosphate groups make up the backbone or sides of the ladder.

• The bases fit in the middle like the teeth of a zipper or the rungs of the ladder.

Nitrogenous Pairs• There are two

groups of base pairs.

• The purines:

Adenine (A)

Guanine (G)• The pyrimidines:

Thymine (T)

Cytosine (C)

Base Pairing

• Adenine (A) always pairs up with thymine (T).

• Cytosine (C) always pairs with guanine (G).

• Purines pair with pyrimidines

An Example…

DNA1: ATG CGC GGG ATT

DNA 2: TAC

GCG CCC TAA

Summary Questions Pt. 2

1. The structure of DNA is called the _________ ___________.

2. A DNA Nucleotide contains ________, _________, and ___________.

3. Adenine always pairs with _______, Cytosine always pairs with ________.

Part 3: Replication

Objectives:• Describe the process of replication

• Identify the products of DNA Replication

DNA replication• DNA replication is the

process by which DNA copies itself.

• It does this right before cell division so that the new cell has the same DNA as the original

• This results in 2 identical strands of DNA, each with 1 of the original strands and 1 of the copies

How does it work?

The steps…

• 1. The double helix unzips.

• 2. The sugar and phosphates bond to make a new backbone.

• 3. Base Pairing: Free floating bases pair up with the bases on the DNA strands. (C-G, A-T)

Let’s see it again!

• Play!

Summary (in class!)

• DNA Replication results in ____________.

• The three steps of Replication are:1. __________________

2. __________________

3. __________________

Part 4: Transcription and Translation

Objectives:

1.Identify the differences between RNA and DNA

2.Identify the different types of RNA molecules

3.Describe the processes of Transcription and Translation

What is RNA?

• RNA, ribonucleic acid, is different from DNA in four major ways:

1. It is single stranded.

2. It can leave the nucleus

3. The sugar is ribose.

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

Types of RNA

• mRNA = messenger RNA is made in the nucleus and, unlike DNA, can leave through the nuclear envelope.

• rRNA = ribosomal RNA makes up ribosomes• tRNA = tranfer RNA delivers amino acids to the

protein to be assembled.

Transcription

•Transcription is the process by which mRNA is made from DNA.

Steps of Transcription1. The process begins

when enzymes unzips part of the molecule of DNA.

2. Free RNA nucleotides form base pairs with the DNA. The mRNA nucleotides bond together.

3. The mRNA strand breaks away and the DNA strands rejoin.

Translation

• The process by which RNA is used to make proteins is known as translation.

• It happens in five steps.

Steps of Translation 1. A ribosome attaches to the mRNA strand. tRNA

approaches the ribosome.

2. The first tRNA molecule attaches to the mRNA.

3. A second molecule attaches and its amino acid peptide bonds to the amino acid of the first tRNA.

4. The ribosome moves down the mRNA and releases the tRNA that no longer has an amino acid attached to it.

5. The process repeats until the stop codon is reached.

What’s a codon?• A group of 3

bases that codes for a specific amino acid

• Amino acids make up proteins

Find the amino acid or command:

• ACC _______________________

• UAG _______________________

• AUG _______________________

• GGG _______________________

• UUA _______________________

• AUC _______________________

• CCC _______________________

Use the circular chart this time

• AUG ___________________________

• AAA ___________________________

• UUU ___________________________

• UAG ___________________________

• CGC ___________________________

• GGA ___________________________

Summary Questions Pt. 4

• RNA differs from DNA in that:– ______________– ______________– ______________– ______________

• Transcription results in ______________• Translation results in ________________• The codon AUG codes for ____________