Molecular Genetics Chapter 12

12.1 DNA: The genetic master

12.2 Replication of DNA

12.3 DNA, RNA and Protein

Comprehension Check• What organic compound group

does DNA belong to?

• What are the building blocks (monomers) of DNA?

History of DNA

Early scientists knew that there was something in cells that controlled the genetic information

They did not know what that was!

History of DNA

Frederick Griffith was studying bacteria (in 1928) and realized that one bacteria could change another, this is called: transformation.

He believed proteins, NOT DNA, controlled this genetic information

He mixed good and bad bacteria in mice to see what would happen Non-harmful Bacteria: Mouse lived Harmful Bacteria: Mouse died Non-harmful Bacteria and Dead Harmful

Bacteria mixed together: Mouse died

History of DNA

Oswald Avery designed an experiment (in 1944) to further test Griffith’s finding He made a solution of the dead harmful

bacteria and treated the solution with enzymes that destroyed all organic compounds except DNA.

Transformation (change) still occurred so he concluded that genetic information was controlled by DNA

History of DNA

Alfred Hershey and Martha Chase (in 1952) used viruses called bacteriophages (a virus that makes bacteria sick) to confirm that DNA is the genetic material Radioactive DNA: Cell infected by these

viruses glowed Radioactive Protein: Cell infected byt these

viruses did not glow

History of DNA

James Watson and Francis Crick (in 1953) develop the double-helix model of the structure of DNA

Their model looks like this:

Current Research

Human Genome Project, finished

Gene Chips Identifying new species Identifying new

genes/Treating diseases Tracing your heredity

Comprehension Check• What was the first major question

scientists had to answer about genetic information?

• What was the second major question?

Structure of DNA (Monomers)

DNA is made up of many repeating units (monomers) called: NUCLEOTIDES

DNA holds the code for making proteins in your body. The order of the nucleotides determines which proteins will be made A nucleotide is a three-part unit made up of . . .

1. Sugar(Deoxyribose) 2. Phosphate group

3. Nitrogen-carrying base

Structure of DNA (Monomers)

Go to Section:

Purines PyrimidinesAdenine Guanine Cytosine Thymine

Go to Section:

•There are 4 different nitrogen bases in DNA: Adenine, Guanine, Cytosine, Thymine

•The bases are classified into two main group based on their size:

•Purines have two nitrogen rings

•Pyrimindines have one nitrogen ring

•Bases always pair in the same way:

ADENINE binds with THYMINE GUANINE binds with CYTOSINE

DNA (the polymer) is a double strand of nucleotides joined by their bases

The phosphate of one nucleotide connects to the sugar of the next nucleotide (forming the sides). EXAMPLE:

Some people think that DNA looks like a ladder, with the bases being the steps and the sugar/phosphates being the sides

Structure of DNA (Polymer)

DNA DNA molecules contain four bases: adenine (A), guanine (G), cytosine (C) and thymine (T). Instead of thymine, RNA molecules that are constructed from DNA contain uracil (U). If the sequence of bases in an RNA molecule is GUCUCA, what was the base sequence of DNA molecule from which it was constructed?

A. CTGTGAB. CAGAGTC. GTCTCAD. ACTCTG

DNA DNA molecules contain four bases: adenine (A), guanine (G), cytosine (C) and thymine (T). Instead of thymine, RNA molecules that are constructed from DNA contain uracil (U). If the sequence of bases in an RNA molecule is GUCUCA, what was the base sequence of DNA molecule from which it was constructed?

A. CTGTGAB. CAGAGTC. GTCTCAD. ACTCTG

Chromosomes There are two different types of cells

Prokaryotic Cells: Bacteria Cells with no nucleus Eukaryotic Cells: More complex cells with a nucleus

The cells of all organisms contain DNA, but some cells contain more than others

Eukaryotic Cells have 100,000 times more DNA than Prokaryotic Cells…..so how does it all fit inside that tiny nucleus???

Chromosomes, only found in eukaryotes, help the DNA pack into the nucleus

Chromosomes are made of two organic compounds: DNA, Proteins (called Histones)

Go to Section:Go to Section:

Comprehension Check• What is the difference between a

prokaryote and a eukaryote?

• The nucleus of a human cell contains 1 meter of DNA. How does all of this DNA fit into a cell’s nucleus?

Comprehension Check• What does the word replication mean?

• What must be occurring in DNA Replication?

• Do you think that this will be a complicated process?

DNA Replication

This is the process by which a DNA molecule makes an EXACT copy of itself. This is important so the “code” can be passed

from one generation to the next. This has to happen every time that a cell divides This process has to be exact so that mutations do

not occur In humans, the entire replication process takes

about 4 hours.

Semi-Conservation Replication

Template

Steps of DNA ReplicationStep #1: The two sides of the strand

are broken apartStep #2: The two inside parts of the

strand are assembledStep #3: The new strands are proofread

by the cell and mistakes are fixed

Comprehension CheckA section of DNA has the following

sequence of bases:G A C C T A G G C T T A A C

Determine the complimentary sequence:C T G G A T C C G A A T T G

Comprehension Check• What does DNA do?/Why do you

need DNA?

THE CENTRAL DOGMA

TRANSCRIPTION

TRANSLATION

Remember, the order to amino acids is determined by the RNA code which is determined by the DNA code:

DNA RNA PROTEINS

What does DNA really do? DNA is found in the nucleus. It codes

for the production of proteins. Proteins are the keys to almost

everything that living cells do! Proteins are actually put together on

the ribosomes. The problem is getting the code out of

the nucleus to the ribosome.

RNA RNA gets the codes in the DNA out to the ribosome

There are three types of RNA, each has a special job in sending the message and making the protein1. mRNA = Messenger RNA2. tRNA = Transfer RNA3. rRNA = Ribosomal RNA

Processes of Protein Synthesis

There are two processes that must occur to make a protein:

1. TRANSCRIPTION: DNA’s code in the nucleus is “copied” by mRNA and is then taken to a ribosome.

2. TRANSLATION: With the help of rRNA, tRNA brings the correct amino acids to the mRNA and the protein is assembled.

Comprehension Check• Why can’t the DNA leave the

nucleus?

• How does the “code” get to the ribosomes?

Remember that RNA is a copy of the code found in DNA, its like a encrypted message

It is NOT single bases in RNA that are important – but groups of 3 called CODONS.

Each codon on mRNA codes for a specific amino acid. (REMEMBER THAT AMINO ACIDS ARE THE MONOMERS OF PROTEINS)

Reading the Code