1. Replication, Transcription, & Translation

2. DNA Replication
Before a cell can divide by mitosis or meiosis, it must first make a copy of its chromosomes.
The DNA in the chromosomes is copied in a process called DNA replication.
Without DNA replication, new cells would have only half the DNA of their parents.
DNA Replication

3. The blue strands represent the original DNA strands.
DNA Replication
The blue strands represent the original DNA strands.
The red strands are the new, synthesized strands.
DNA
Replication
Replication
DNA Replication

4. Click the image to view a video clip.
DNA Replication
Click the image to view a video clip.
DNA Replication

5. DNA is copied during interphase prior to mitosis and meiosis.
Copying DNA
DNA is copied during interphase prior to mitosis and meiosis.
It is important that the new copies are exactly like the original molecules.
Copying DNA

6. Copying DNA New DNA molecule Original DNA Strand Free Nucleotides
New DNA Strand
Original DNA Strand
Original DNA
Copying DNA

7. Genes and Proteins
The sequence of nucleotides in DNA contain information that is put to work through the production of proteins.
Proteins fold into complex, three-dimensional shapes to become key cell structures and regulators of cell functions.
Genes and Proteins

8. Genes and Proteins
Some proteins become important structures, such as the filaments in muscle tissue.
Other proteins, such as enzymes, control chemical reactions that perform key life functions—breaking down glucose molecules in cellular respiration, digesting food, or making spindle fibers during mitosis.
Genes and Proteins

9. In fact, enzymes control all the chemical reactions of an organism.
Genes and Proteins
In fact, enzymes control all the chemical reactions of an organism.
Thus, by encoding the instructions for making proteins, DNA controls cells.
Genes and Proteins

10. Remember, proteins are polymers of amino acids.
Genes and Proteins
Remember, proteins are polymers of amino acids.
The sequence of nucleotides in each gene contains information for assembling the string of amino acids that make up a single protein.
Genes and Proteins

11. RNA
RNA like DNA, is a nucleic acid. RNA structure differs from DNA structure in three ways.
First, RNA is single stranded—it looks like one-half of a zipper—whereas DNA is double stranded.
RNA

12. The sugar in RNA is ribose; DNA’s sugar is deoxyribose.

13. RNA
Both DNA and RNA contain four nitrogenous bases, but rather than thymine, RNA contains a similar base called uracil (U).
Uracil forms a base pair with adenine in RNA, just as thymine does in DNA.
RNA

14. The workers for protein synthesis are RNA molecules.
DNA provides workers with the instructions for making the proteins, and workers build the proteins.
The workers for protein synthesis are RNA molecules.
RNA

15. RNA
RNA takes the instructions from DNA (telling how the protein should be assembled), then—amino acid by amino acid—RNA assembles the protein.
RNA

16. There are three types of RNA that help build proteins.
Messenger RNA (mRNA), brings instructions from DNA in the nucleus to the cell’s factory floor, the cytoplasm.
On the factory floor, mRNA moves to the assembly line, a ribosome.
RNA

17. RNA
The ribosome, made of ribosomal RNA (rRNA), binds to the mRNA and uses the instructions to assemble the amino acids in the correct order.
RNA

18. RNA
Transfer RNA (tRNA) is the supplier. tRNA delivers amino acids to the ribosome to be assembled into a protein.
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RNA

19. Transcription
In the nucleus, enzymes make an RNA copy of a portion of a DNA strand in a process called transcription.
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Transcription

20. Transcription
DNA strand
RNA strand
Transcription

21. Transcription
The main difference between transcription and DNA replication is that transcription results in the formation of one single-stranded RNA molecule rather than a double-stranded DNA molecule.
Transcription

22. The Genetic Code
The nucleotide sequence transcribed from DNA to a strand of mRNA acts as a genetic message, the complete information for the building of a protein.
The Genetic Code

23. The Genetic Code
Biochemists began to crack the genetic code when they discovered that a group of three nitrogenous bases in mRNA code for one amino acid. Each group is known as a codon.
64 combinations are possible when a sequence of three bases is used; thus, 64 different mRNA codons are in the genetic code.
The Genetic Code

24. The Genetic Code

25. More than one codon can code for the same amino acid.
The Genetic Code
Some codons do not code for amino acids; they provide instructions for making the protein.
More than one codon can code for the same amino acid.
However, for any one codon, there can be only one amino acid.
The Genetic Code

26. All organisms use the same genetic code.
The Genetic Code
All organisms use the same genetic code.
This provides evidence that all life on Earth evolved from a common origin.
The Genetic Code

27. Translation takes place at the ribosomes in the cytoplasm.
The process of converting the information in a sequence of nitrogenous bases in mRNA into a sequence of amino acids in protein is known as translation.
Translation takes place at the ribosomes in the cytoplasm.
Translation

28. Translation
In prokaryotic cells, which have no nucleus, the mRNA is made in the cytoplasm.
In eukaryotic cells, mRNA is made in the nucleus and travels to the cytoplasm.
Translation

29. Translation
In cytoplasm, a ribosome attaches to the strand of mRNA like a clothespin clamped onto a clothesline.
Translation

30. This is the role of transfer RNA (tRNA).
The Role of tRNA
For proteins to be built, the 20 different amino acids dissolved in the cytoplasm must be brought to the ribosomes.
This is the role of transfer RNA (tRNA).
The Role of tRNA

31. Chain of RNA nucleotides
The Role of tRNA
Each tRNA molecule attaches to only one type of amino acid.
Amino acid
Chain of RNA nucleotides
Transfer RNA molecule
Anticodon
The Role of tRNA

32. The Role of tRNA
As translation begins, a ribosome attaches to the starting end of the mRNA strand. Then, tRNA molecules, each carrying a specific amino acid, approach the ribosome.
When a tRNA anticodon pairs with the first mRNA codon, the two molecules temporarily join together.
The Role of tRNA

33. The Role of tRNA
Ribosome
mRNA codon
The Role of tRNA

34. AUG signals the start of protein synthesis.
The Role of tRNA
Usually, the first codon on mRNA is AUG, which codes for the amino acid methionine.
AUG signals the start of protein synthesis.
When this signal is given, the ribosome slides along the mRNA to the next codon.
The Role of tRNA

35. The Role of tRNA
Methionine
tRNA anticodon
The Role of tRNA

36. The Role of tRNA
A new tRNA molecule carrying an amino acid pairs with the second mRNA codon.
Alanine
The Role of tRNA

37. The amino acids are joined when a peptide bond is formed between them.
The Role of tRNA
The amino acids are joined when a peptide bond is formed between them.
Methionine
Alanine
Peptide bond
The Role of tRNA

38. The Role of tRNA
A chain of amino acids is formed until the stop codon is reached on the mRNA strand.
Stop codon
The Role of tRNA

39. Replication = copying DNA Transcription = using DNA to make RNA
Summary
Replication = copying DNA
Transcription = using DNA to make RNA
Translation = using RNA to make protein
The Role of tRNA