Ch. 10: Nucleic Acids and Protein Synthesis

- DNA controls the production of proteins within the cell.

- These proteins form the structural units of cells and control the chemical processes.

DNA’s 2 primary functions:

1. Store and use information to direct activities of the cell.

2. Make an exact copy of itself to pass on to new cells.

Where is DNA stored in the cell?

In the cell’s nucleus.

Structure of DNA

- DNA is an organic molecule made up of repeating subunits called nucleotides.

- Nucleotide: 3 main parts:

1) Sugar molecule called deoxyribose

2) Phosphate group

3) Nitrogen base

- There are 4 nitrogen-containing bases found in DNA nucleotides:

1. Adenine (A)2. Cytosine (C)3. Thymine (T)4. Guanine (G)

- The 4 nitrogen bases are placed into 2 structural groups:

1) Purines: double ring of carbon (A,G)2) Pyrimidines: single ring of carbon (T,C)

- DNA is a double helix (twisted ladder)

Base Pairing Rules:

A-T

C-G

Or vice versa

-Double ring always

Bonds w/ single

ring

DNA Replication- The process of duplicating a molecule of DNA

1) An enzyme called DNA helicase attaches to the DNA molecule and breaks the bonds or “unzips” the double helix.

2) In the nucleus of the cell, free-floating nucleotides bond to the “unzipped” portion of the DNA molecule.

3) The replication is complete after an enzyme called DNA polymerase bonds all nucleotides together forming 2 DNA molecules, both with one “old strand” and one “new strand.”

Accuracy and Repair

1) The cell has a built-in “proof-reading” function.

2) About 1 error per billion nucleotides.

3) Body heat, radiation, chemicals, etc. can damage your DNA.

4) A group of 20 or more enzymes designed to seek out and replace damaged nucleotides.

Homework- due Tues.

Research on the web, in magazines or

books something interesting about DNA.

Ex:

- How is DNA used to solve crimes?

- What are some things that can happen as a result of DNA damage?

- What is the human genome project?

- What are some things modern science is studying about DNA?

• Some helpful search words for the web:

- DNA

- Nucleic Acids

- Human genome project

- DNA and forensic science

- Neatly write or type 1-2 paragraphs describing what you found out. Be prepared to share in class on Tues.

- Don’t forget to cite your sources!

Section 10-2 RNAHow does RNA differ from DNA?

*RNA is a nucleic acid made up of repeating

nucleotides. However, the sugar molecule of every RNA nucleotide is __________, whereas DNA nucleotides contain __________ _____________.

*______________, a nitrogen-containing pyrimidine (one ring of carbon), usually replaces thymine in RNA. Therefore, __________ pairs with ______________ in RNA.

3 Types of RNA

• Type of RNA that consists of RNA nucleotides in the form of a single uncoiled chain. This RNA is responsible for carrying genetic information from the DNA in the nucleus to the cytosol of a eukaryotic cell:

_____________________(______).

• This RNA consists of a single chain of about 80 RNA nucleotides folded into a hairpin shape that binds to specific amino acids. There are about 45 varieties of this RNA______________(_______).

• This is the most abundant form of RNA. It consists of RNA nucleotides in a globular form. Joined by proteins, it makes up the ribosomes where proteins are made:

_________________(______).

Transcription Let’s think of transcription as an analogy.

Think of DNA as a reference book in a library. These books can not be taken out because they are very valuable and may risk getting damaged if they leave the confines of the library. If DNA were to leave the nucleus and enter the cytosol, it would enter an environment that would make it more vulnerable to getting damaged from radiation and chemicals.

So, how do we get information from the reference book/DNA without taking it

out of the library/nucleus?We make a copy.

This is where mRNA enters the picture. The RNA is the messenger, or copier, responsible for carrying the genetic information from DNA in the nucleus to the cytosol, where it can be used to produce proteins.

Transcription is…

We will now go through the process of transcription together. Please fill in notes where indicated.

http://www-class.unl.edu/biochem/gp2/m_biology/animation/gene/gene_a2.html

Some things to remember:

• As in replication, a small section of the DNA double helix unwinds, and the bases on the 2 strands are exposed.

• RNA nucleotides line up in the proper order by hydrogen-bonding to their complementary bases on DNA.

• The nucleotides are joined together by a DNA-dependent __________ _________, and __________ results.

How is Transcription different from Replication?

• In transcription, only ___ strand of DNA is transcribed into mRNA (remember that RNA is a single-stranded molecule).

• The DNA strand that is transcribed is called the ___________ __________.

What determines where transcription will begin and end?• In other words, where does one gene start and

the next begin?• The starting point of a gene is marked by a

certain base sequence which is called a _________ ____________.

• These sites act as a “start sign” . Similarly, there are other base sequences at the end of a gene that signal a to mRNA synthesis.

• This DNA region is referred to as a _________ _____________.

What are the products of transcription?

• The transcripts are the different types of RNA molecules, including mRNA, tRNA and rRNA.

• Even though the instructions are for making a protein are copied from DNA into mRNA, all 3 types of RNA are involved in the synthesis of proteins.