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Molecular Genetics Chapter 12

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1 Molecular Genetics Chapter 12
12.1 DNA: The genetic master 12.2 Replication of DNA 12.3 DNA, RNA and Protein

2 Comprehension Check What organic compound group does DNA belong to?
What are the building blocks (monomers) of DNA?

3 History of DNA Early scientists knew that there was something in cells that controlled the genetic information They did not know what that was!

4 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

5 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

6 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

7 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:

8 Current Research Human Genome Project, finished Gene Chips
Identifying new species Identifying new genes/Treating diseases Tracing your heredity

9 Comprehension Check What was the first major question scientists had to answer about genetic information? What was the second major question?

10 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

11 Structure of DNA (Monomers)
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 Purines Pyrimidines Adenine Guanine Cytosine Thymine Go to Section: Go to Section:

12 Structure of DNA (Polymer)
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

13 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? CTGTGA CAGAGT GTCTCA ACTCTG

14 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? CTGTGA CAGAGT GTCTCA ACTCTG

15 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… 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:

16 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?

17 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?

18 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.

19 Semi-Conservation Replication

20 Steps of DNA Replication
Step #1: The two sides of the strand are broken apart Step #2: The two inside parts of the strand are assembled Step #3: The new strands are proofread by the cell and mistakes are fixed

21 Comprehension Check A 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

22 Comprehension Check What does DNA do?/Why do you need DNA?

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

24 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.

25 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 protein 1. mRNA = Messenger RNA 2. tRNA = Transfer RNA 3. rRNA = Ribosomal RNA

26 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.

27 Comprehension Check Why can’t the DNA leave the nucleus?
How does the “code” get to the ribosomes?

28 Reading the Code 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)

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