Heredity

B-4.3 Explain how DNA functions as the code of life and the

blueprint for proteins. (Focus on DNA replication) B-4.4:

Summarize the basic process involved in protein synthesis (including transcription and translation).

Key Concepts Ø DNA Replication Ø Protein Synthesis Ø Transcription:

Ø messenger RNA (mRNA) Ø Translation:

Ø ribosomal RNA (rRNA) Ø codons Ø transfer RNA (tRNA) Ø anticodon site Ø peptide bond Ø stop codon

• 

What you already know…

Students have no previous knowledge of this concept. It has not been addressed in previous grades.

It is essential for you to know… •  The specificity of proteins is determined by the order of the

nitrogenous bases found in the DNA. •  DNA can function as the code of life for protein synthesis

or the process of DNA replication, which ensures that every new cell has identical DNA.

•  DNA replication is carried about by a series of enzymes. •  Transcription is the process by which a portion of the

molecule of DNA is copied into a complementary strand of RNA.

•  Translation is the process of interpreting the genetic message and building the protein and begins when the mRNA attaches to a ribosome, which contains proteins and ribosomal RNA (rRNA), in the cytoplasm.

Objectives Summarize the role of DNA as the code of life. Summarize the process of DNA replication. Interpret illustrations of the processes of transcription, translation, and protein synthesis. Compare the processes of transcription and translation. Sequence the steps of transcription and translation. Explain the significance of each step to the overall process of protein synthesis.

Vocabulary Words 1.  Replication 2.  DNA polymerase 3.  Central dogma 4.  RNA 5.  Transcription 6.  RNA polymerase 7.  Messenger RNA

(mRNA)

8.  Ribosomal RNA (rRNA)

9.  Transfer RNA (tRNA) 10. Translation 11. Codon 12. Stop codon 13. Start codon 14. Anticodon 15. Peptide bond

DNA Replication The double helix structure explains how DNA replication can occur.

The two strands of DNA are complementary. – They each can be used to make a copy of the

other.

DNA Replication

Before a cell divides, its DNA has to be duplicated, called DNA replication.

– DNA molecule separates into two strands

– Two new complementary strands are produced via base pairing.

– Happens during Interphase (S) of the Cell Cycle.

DNA Replication: Prokaryotes In prokaryotes, DNA replication starts at one point on the chromosome and proceeds in two directions until the entire chromosome is copied.

DNA Replication: Eukaryotes In eukaryotes, DNA replication starts at hundreds of places and proceeds in two directions until the entire chromosome is copied.

DNA Replication

•  Enzymes “unzip” the DNA.

•  Involves a host of enzymes and regulatory proteins.

•  Principle enzyme involved is called DNA polymerase.

Websites

DNA Replication Animation from your textbook

DNA Replication: Howard Hughes Medical

Institute

Practice

What would be the complimentary DNA strand to the following nucleotide sequcence?

A T C C G A T T A G G C C C A T A C G

Answer

A T C C G A T T A G G C C C A T A C G T A G G C T A A T C C G G G T A T G C

DNA Replication Problems 1.  What is the first step in DNA replication? 2.  What enzyme matches the bases of free

nucleotides to the bass on the parent strand?

3.  If the DNA double helix were a twisted ladder, what would the sides be composed of?

4.  If the DNA double helix were a twisted ladder, what would the rungs be composed of?

Complete the following Nucleotide Base Abbreviation Complementary Base

T

C

A

G

Central Dogma In living things, there is a one way flow of information from DNA à Proteins. This is called Central Dogma. Proteins are made in essentially two main steps: •  ¬ Transcription •  ¬ Translation

Transcription Transcription is the process of copying DNA into RNA.

–  So that translation can happen next

Happens in the nucleus of eukaryotes and the cytoplasm of prokaryotes.

–  Wherever the DNA is

Transcription RNA polymerase binds to DNA at promoter regions & separates the strands.

RNA polymerase then uses one strand of DNA as a template to make RNA.

Uses base-paring: A=U G=C

Let’s Do Some Practice

Transcribe the following DNA strands:

A-G-G-T-A-C-C-C-G-A-A-T-T-T

G-G-C-C-A-A-T-T-A-A-T-T-G-C

Answers

A-G-G-T-A-C-C-C-G-A-A-T-T-T U-C-C-A-U-G-G-G-C-U-U-A-A-A

G-G-C-C-A-A-T-T-A-A-T-T-G-C C-C-G-G-U-U-A-A-U-U-A-A-C-G

Translation Once the mRNA is formed, it will leave the nucleus (of a eukaryote) and go to the ribosome, where the second part of protein synthesis takes place, translation.

The Genetic Code Proteins are made (synthesized) by joining amino acids into long chains called polypeptides.

– Protein synthesis

The language of mRNA is called the genetic code.

– Comprised of the letters A, U, C and G – Every combination of three letters is called a

codon.

The Genetic Code UCGCACGGU

Read three bases at a time.

UCG-CAC-GGU Codons represent different amino acids.

Serine-Histidine-Glycine Joined by peptide bonds.

The Genetic Code There are 64 possible codons for the genetic code. (4 x 4 x 4 = 64)

Some amino acids can be specified by more than one codon.

AUG is the start codon. -methionine

Three stop codons. -can you find them?

The Genetic Code Let’s Practice

•  DNA Sequence is TACGCATGGAAT

•  What is the mRNA sequence?

•  AUG CGU ACC UUA

•  What amino acids do they code for?

•  Methionine-arginine-threonine-leucine

Translation

•  Translation is the decoding of a mRNA molecule into a protein.

•  One major molecule in this process is the tRNA molecule.

•  Happens in the ribosome of the cell.

Translation •  mRNA is made from DNA

•  mRNA comes out of the nucleus and attaches to a ribosome.

•  tRNA brings in an anticodon that is complementary to the mRNA codon sequences. With each anticodon is the amino acid that the mRNA codon codes for. –  Codon is AUG, the anticodon is UAC bringing methionine with it

to attach to mRNA.

•  Polypeptide chain grows until it reaches a stop codon.