CHAPTER 10

DNA, RNA, and Protein Synthesis

http://www.3dscience.com/3D_Models/Biology/DNA/DNA_with_Phosphate.php

Section 1 Vocabulary Pretest1. Virulent2.

Transformation3. Bacteriophage

A. Viruses that infect bacteria

B. Transfer of DNA fragments from cell to cell

C. Virus capable of causing disease

Answer key

1. Virulent C2. Transformation B3. Bacteriophage A

Discovery of DNA

Three experiments led to the discovery of DNA as the hereditary factor that Mendel described in his experiments with pea plants. Griffith’s Experiment (1928)—showed that

hereditary material can pass from one bacterial cell to another (transformation)

Avery’s Experiment (1940s)—showed that DNA is the hereditary material that transfers information between bacterial cells.

Hershey and Chase’s Experiment (1952)– confirmed that DNA, and not protein, is the hereditary material in all cells.

Section 2 Vocabulary Pretest

1. Nucleotide

2. Deoxyribose

3. Nitrogenous base

4. Purine

5. Pyrimidine

6. Base-pairing rules

7. Complementary base pair

8. Base sequence

A. Sugar found in DNA

B. Consists of a sugar, phosphate and nitrogenous base

C. Single ring nitrogenous base pair

D. Double ring nitrogenous base pair

E. Rule stating: A always pairs w/ T and C always pairs w/ G

F. Order of bases on an DNA strand

G. Contains nitrogen and carbon atoms and is found on the rungs of a DNA ladder

H. A and T C and G

Answer Key

1. Nucleotide B2. Deoxyribose A3. Nitrogenous base G4. Purine D5. Pyrimidine C6. Base-pairing rules E7. Complementary base pair H8. Base sequence F

DNA Structure

By 1950, we knew DNA was the hereditary molecule.

How did it work? How did it replicate, store and transmit hereditary information and direct cell function?

The answer is found in the unique structure of DNA.

http://www.med.unc.edu/pmbb/DNA_Day/mission.html

The structure of DNA was discovered in 1953 by James Watson and Francis Crick.

http://svhs.ucps.k12.nc.us/academics/science.php

Deoxyribonucleic Acid

Described as a double helix (twisted ladder).

Formed by two long strands of repeating subunits called nucleotides.

http://www.biologyjunction.com/nucleotide_model_preap.htm

http://www.biojobblog.com/tags/dna/

Each nucleotide has three parts: Five-carbon sugar

called deoxyribose Phosphate group

(phosphorous bonded to 4 oxygens)

Nitrogenous base (either adenine, thymine, guanine or cytosine)

http://www.biologyjunction.com/nucleotide_model_preap.htm

http://asm.wku.edu/pix/pix.htm

The sides of the ladder are formed by covalently bonding the sugar of one nucleotide to the phosphate of another.

Sugar

Phosphate

Covalent bond

http://academic.brooklyn.cuny.edu/biology/bio4fv/page/molecular%20biology/dna-structure.html

The nitrogenous bases form the rungs of the ladder.

There are four types of nitrogen bases: Thymine Cytosine Adenine Guanine

http://student.ccbcmd.edu/~gkaiser/biotutorials/dna/fg4.html

Adenine and Guanine have a double ring of carbon and nitrogen atoms and are called purines.

Thymine and Cytosine have a single ring of carbon atoms and nitrogen atoms. They are called pyrimidines

http://blog.dearbornschools.org/biologyblog/2010/02/09/february-9-2010/

The bases pair together to form the rungs of the DNA ladder.

Hydrogen bonds hold them together. They always pair according to the following

base-pairing rules discovered by Erwin Chargaff in 1949: A – T C – G

Note: since this pairing guarantees that a purine always pairs with a pyrimidine, the rungs are always the same length

http://academic.brooklyn.cuny.edu/biology/bio4fv/page/molecular%20biology/dsDNA.jpg

The base pairs of A/T and C/G are called complementary base pairs.

The order of base pairs on a chain of DNA is called its base sequence. Because of its base pairing pattern,

one strand of DNA can serve as a template for making a new complementary strand.

This is how DNA replicates itself.

A strand of DNA has the following sequence:C T G G A CWhat is the sequence of the complementary strand?G A C C T G

http://www.fhcrc.org/education/courses/cancer_course/basic/img/dna.gif

Section 3 Vocabulary Pretest

1. DNA replication2. Helicase3. Replication fork4. DNA polymerase5. Semi-

conservative replication

6. Mutation

A. A change in a nucleotide sequence of DNA

B. Enzyme that separates two strands of DNA

C. Enzyme that adds nucleotide bases to copying strands of DNA

D. Point where two DNA strands separate

E. Process of copying DNAF. DNA replication that results in

one old and one new strand in each copied molecule

Answer Key

1. DNA replication E2. Helicase B3. Replication fork D4. DNA polymerase C5. Semi-conservative replication F6. Mutation A

DNA Replication

DNA replication is the process by which DNA is copied in a cell before a cell divides by mitosis, meiosis, or binary fission.

Steps: Helicases (enzymes)

separate the DNA strands by breaking hydrogen bonds between base pairs. This creates an open area of DNA called a replication fork. http://www.nvo.com/jin/nss-folder/scrapbookcell/DNA

%20Replication.jpg

DNA polymerases (more enzymes) add complementary nucleotides to each of the original sides. Notice that synthesis on each strand moves in opposite directions.

DNA polymerase enzymes fall off and the two new strands completely separate. An enzyme called DNA ligase must fill in gaps created on the strand being copied in the opposite direction.

The end result is two new identical strands of DNA.

This type of replication is called semi-conservative replication because each of the new DNA molecules has kept (or conserved) one of the two (or semi) original DNA strands.

http://jc-biology.blogspot.com/2011/02/replication-of-dna-summary.html

Speed of Replication

DNA adds nucleotides at a rate of 50 per second.

However, at this rate it would take 53 days to replicate a large human chromosome.

Therefore, replication must begin at several, usually thousands, of different points, or origins, at the same time.

Any change in the nucleotide sequence of a DNA molecule is called a mutation. DNA polymerase can check and correct

mistakes made during replication. However, mistakes do happen. Mistakes can be spontaneous or caused by

environmental factors (radiation, chemicals, etc.)

Mutations can be helpful, harmful or harmless.

Mistakes made in genes that control cell division can lead to tumors.

Mutations

Section 4 Vocabulary Pretest

1. Ribonucleic acid

2. Transcription3. Translation4. Protein

synthesis5. Ribose6. Messenger

RNA7. Transfer RNA

A. Nucleic acid important in protein synthesis

B. Sugar found in RNAC. RNA that carries instructions

from the nucleus to ribosomesD. Process of making an RNA

molecule from a DNA templateE. RNA that assembles an amino

acid chainF. Process of assembling a

protein from a coded RNA message

G. DNA RNA protein

8. RNA polymerase

9. Promoter10. Termination

signal11. Genetic code12. Codon13. Anticodon14. Genome

H. An organism’s entire gene sequence

I. Sequence of nucleotides at the end of a gene

J. Sequence of nucleotides that start transcription

K. 3-nucleotide sequence on mRNA that encodes an amino acid

L. 3-nucleotide sequence on tRNA that complements a codon

M. Specifies the amino acid sequence of a protein

N. Enzyme that catalyzes the formation of RNA

Pretest continued

Answer Key

1. Ribonucleic acid A

2. Transcription D

3. Translation F

4. Protein synthesisG

5. Ribose B

6. Messenger RNA C

7. Transfer RNAE

8. RNA polymerase N

9. Promoter J

10. Termination signal I

11. Genetic code M

12. Codon K

13. Anticodon L

14. Genome H

Protein Synthesis (Big Picture)

Cells make proteins. The instructions to

make a protein are on the DNA in the nucleus.

Ribosomes in the cytoplasm make the proteins

Cells MUST be able to get the instructions from the DNA inside the nucleus out to the ribosomes.

RNA is the messenger !!!

http://www.sciencephoto.com/images/download_lo_res.html?id=670020523

RNA Structure and Function

RNA is different from DNA in 4 ways RNA sugar is

ribose Uracil replaces

thymine as a base RNA is single

stranded RNA is shorter

than DNA

DNA vs. RNA

DNA RNA Double

Single Deoxyribose

Ribose Thymine

Uracil Longer

Shorter

Types of RNA

Three major types of RNA Messenger RNA (mRNA) —carries

instructions for making a protein from a gene in the nucleus to a ribosome in the cytoplasm

Ribosomal RNA (rRNA) —part of a ribosome

Transfer RNA (tRNA) —transfers amino acids to the ribosome to make a protein.

mRNA is made fromDNA in the nucleus. It carries the messagefor making a protein out of the nucleus to a ribosome in the cytoplasm

rRNA is part of the ribosome.

tRNA is folded with many nucleotidebases. However, we emphasize the three at the bottom.

Protein Synthesis

Forming proteins based on information in DNA and carried out by RNA is called protein synthesis.

DNA RNA protein It involves two

processes: Transcription Translation

Transcription

Transcription —the genetic code is copied or “transcribed” onto a mRNA in the cell nucleus.

Three steps: RNA polymerase (enzyme) binds to a specific

site on a DNA molecule called a promoter. This causes DNA to unwind.

RNA polymerase uses the base-pairing rules to add the RNA nucleotides that match the DNA code (A/U; C/G)

RNA polymerase stops at a termination signal that marks the end of a gene.

Transcriptionhttp://meyerbio1b.wikispaces.com/Transcription+and+Translation

Reading the Code

The code on the mRNA must next be “read” during the process of translation.

This genetic code tells us how a sequence of bases on a DNA molecule (or its RNA messenger) corresponds to a particular amino acid.

The code is read three bases at a time. Each 3 base sequence that codes for an amino acid is called a codon.

Codons in mRNA

Notice AUG is the start codon UAA, UAG, and UGA are the stop codons.

Amino Acids

The genetic code rules are the same for nearly all living things.

The same codons always code for the same amino acids.

There are 20 different amino acids. A chain of amino acids makes up a

polypeptide. Polypeptides join and twist to make up

proteins. It is tRNA and the ribosomes that assemble

the proteins during translation.

Three bases at one end of a tRNA are complementary to a codon on the mRNA. They are called an anticodon.

The specific amino acid that the codon codes for is attached to the top of the tRNA

http://www.personal.psu.edu/staff/d/r/drs18/bisciImages/index.html

A U G G G A C C U

Translation

Translation —the making of a protein Steps:

Initiation —ribosomal subunits, mRNA and the tRNA carrying methionine (amino acid of the start signal AUG) bind together.

Elongation —the tRNA carrying the amino acid specified by the next codon binds. Peptide bonds form between the amino acids beginning the chain. This continues until a termination signal is reached.

Termination —stop codon is reached Disassembly – the ribosome complex falls apart

and the peptide is released.

http://www.emc.maricopa.edu/faculty/farabee/biobk/biobookprotsyn.html

Recap: Protein Synthesis: Big Picture

The Human Genome

Genome —the complete genetic material contained in an individual.

The entire Human Genome consists of 3.2 billion base pairs. We now know the order of these base pairs and have discovered that humans have approximately 30,000 genes.

We now need to learn where and when human cells use each of the proteins coded for in the genome.

This can help diagnose, treat, and prevent many genetic disorders.