Unit 5: DNA and Protein Synthesis

What is DNA?

• DNA is an acronym that stands for deoxyribonucleic acid.

• It indirectly controls all the functions of your body.

The history…

• In the early 1950’s scientists thought that proteins were the genetic material.

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

More history…

• In 1953, James Watson and Francis Crick claimed to have discovered 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.

DNA structure

• DNA is a double helical structure.

• It looks like a twisted ladder.

A close-up…

DNA is Made of Nucleotides

• Nucleotides have three parts:

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

2. A phosphate group

3. A nitrogenous base

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).

DNA replication• DNA replication is the

process via which DNA copies itself.

• 1. The double helix unzips.• 2. Bonding of Bases: The

sugar and phosphates of adjacent nucleotides bond together covalently to make the new backbone.

• 3. Base Pairing: Free floating bases pair up with the bases on the DNA strands.

From DNA to Protein

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

1. It is single stranded.

2. The sugar is ribose.

3. 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

• This is a three step process.

• Transcription is the process via 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 via 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?• Any three

bases (ATCG or U) are called codons because they code for amino acids.

• You can use the chart to identify the amino acid which any codon codes for.

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 ___________________________

The other chart…