1. RNA & Protein Synthesis
Chapter 13

2. 13.1: RNA

3. The Role of RNA
The structure of DNA itself does not explain how a gene actually works.
The answer came with the discovery of another nucleic acid, RNA
RNA- Ribonucleic acid

4. Comparing DNA & RNA
Both are made of nucleotides, linked together or not
3 important differences
Different sugars
DNA- deoxyribose
RNA- ribose

5. DNA is double stranded, RNA is single stranded Different bases
DNA has thymine
RNA has uracil
All other bases
are the same

6. DNA cannot leave the nucleus, but the directions on building important molecules need to be carried to other parts of the cell.
RNA acts like disposable copies of genetic information for these directions to be used.

7. Functions of RNA
RNA has many functions, but they are all involved in one main role- protein synthesis.

8. 3 types Messenger RNA (mRNA) Ribosomal RNA (rRNA) Transfer RNA (tRNA)
Produced in the nucleus
Complementary to DNA
Carries the instructions found in DNA from the nucleus to other parts of the cell
Ribosomal RNA (rRNA)
Makes up the 2 subunits of a ribosome
Ribosomes are the organelles that assemble proteins
Transfer RNA (tRNA)
Transports amino acids found in the cell to the ribosome
Uses the coded message from mRNA

9. RNA Synthesis
Understanding how RNA and proteins are made is essential to understanding how genes work.

10. transcription
Most of the work of making RNA happens during the process of transcription
Transcription- segments of DNA serve as templates to produce complementary RNA strands
Transcription requires the use of an enzyme called RNA polymerase
Binds to DNA, separating the bases by breaking the hydrogen bonds
Uses one strand of the DNA to assemble a complementary chain of mRNA nucleotides

12. promoters
RNA polymerase does not bind to just anywhere on the DNA molecule.
There are regions along the DNA strand called promoters that act as signals to show where the enzyme should start building RNA.
There are similar signals that also tell the enzyme to stop transcription.

13. RNA Editting RNA molecules require some editing before being read.
Bits and pieces are cut out and pieced together before they are used in the next step of protein synthesis.

14. 2 portions Introns- cut out and discarded
Exons- remaining pieces spliced together to form the final strand of mRNA

15. Biologists don’t have a complete answer as to why cells use energy to make a large RNA molecule and then throw parts of that molecule away.
Some pre-mRNA molecules may be cut and spliced in different ways in different tissues, making it possible for a single gene to produce several different forms of RNA.
Introns and exons may also play a role in evolution, making it possible for very small changes in DNA sequences to have dramatic effects on how genes affect cellular function.

16. 13.2: Ribosomes & protein Synthesis

17. The Genetic code
The first step in decoding genetic messages is to transcribe DNA into RNA
This transcribed information contains a code for making proteins
Proteins are made by linking amino acids together in long chains called polypeptide chains
There are as many as 20 different amino acids commonly found in polypeptide chains

19. The specific order the amino acids are joined together determine the properties of different proteins.
The sequence can affect the shape in which determines its function.

20. We read the genetic code by looking at 3 bases at a time
The language used in making proteins is called the genetic code which is made up of 4 different letter or bases (A, C, G, & U).
We read the genetic code by looking at 3 bases at a time
Codon- 3 base long message found on mRNA
Codes for amino acids

21. How to read codons
There are 4 different bases in RNA, so there are 64 different combinations of 3 base codons
Some amino acids can be specified by multiple codons
Leucine can be coded by the codons UUA, UUG, CUU, CUC, CUA, & CUG.
Some may be more specific with only one codon combination
Tryptophan can only be coded by UGG.

23. Start & stop codons
These act as punctuation marks for the genetic code.
Methionine is the start codon (AUG) that will signal the beginning of a new polypeptide chain.
All polypeptide chains begin with methionine.
Stop codons will signal an end to a polypeptide chain.
UGA, UAA, & UAG

24. translation
mRNA contains the instructions that give the order in which amino acids should be linked together.
Ribosomes use the sequence of codons to assemble amino acids into polypeptide chains.
Translation- decoding of codons into a polypeptide chain to eventually become a protein

25. Steps in translation
Translation begins when a ribosome attaches to an mRNA molecule.
Each codon will pass through the ribosome giving the directions for each amino acid.

26. tRNA brings the proper amino acids to the ribosome based on the codons read.
tRNA molecules can only bring one amino specific amino acid at a time
tRNA has 3 unpaired bases that are complementary to codons found on
mRNA
These 3 unpaired bases are
called anticodons
Pairs with codons showing exactly what sequence of amino acids in the polypeptide chain

27. Amino acids are brought to the ribosome one at a time and linked together.
The chain continues to grow until the ribosome reads a stop codon which signals it to stop and release the polypeptide chain.

28. The molecular basis of heredity
The central dogma of molecular biology is that the information is transferred from DNA to RNA to proteins.
This illustrates or explains gene expression.
Putting genetic information in action for living cells
One of the most interesting discoveries about molecular biology is the near-universal nature of the genetic code
All organisms use the same 4 letter/base genetic language and protein synthesis process.

29. 13.3: Mutations

30. Types of mutations
Cells can make mistakes in copying DNA, transcribing DNA, and even translating DNA.
Mutations- heritable changes in genetic information
Mutations can come in many different forms but fall in 2 basic categories
Those that produce changes in single genes
Those that produce changes in whole chromosomes

31. Gene mutations
Mutations that involve changes in one or a few nucleotides are known as point mutations because they occur at a single point in the DNA sequence.
They generally occur during replication.
2 types

32. Substitution- one base is changed to a different base
Silent- amino acid does not change
GGU changes to GGA but still codes for glycine

33. Missense- amino acid does change
CAC changes to CAG which changes Histidine to Glutamine

34. Nonsense- amino acid changes to a stop codon
UGU changes to UGA which changes the amino acid Cysteine into a stop codon to early

35. Frameshift mutations- shifts the “reading frame” of the genetic message
Insertion- base is added to the sequence
Deletion- base is removed from the sequence
Changes almost every amino acid after the mutation and can alter a protein so much that it is unable to function properly

36. Chromosomal mutations
Involve the change in the number or structure of chromosomes
Can change the location of genes or the number of copies of genes
4 types

37. Deletion- whole segments of chromosomes are deleted, genes can be lost
Duplication- segments of chromosomes are replicated and remain part of the chromosome
Inversion- reverses segments of chromosomes so that they read backwards
Translocation- segments of one chromosome are removed and attached to a different chromosome

38. Effects of mutations
Genetic material can be altered by natural events or by artificial means.
Mutations may or may not affect organisms

39. Many mutations are produced by errors in genetic processes such as DNA replication.
The cellular machinery that replicates DNA inserts an incorrect base roughly once in every 10 million bases.
Small changes in genes can gradually accumulate over time.
Stressful environmental conditions may cause some bacteria to increase mutation rates.

40. mutagens
Some mutations arise from mutagens- chemical or physical agents in the environment.
Chemical- pesticides, some alkaloids, tobacco smoke, pollutants
Physical- electromagnetic radiation such as X- rays and UV light

41. Harmful & helpful mutagens
The effects of mutations on genes vary widely.
Some have little or no effect
Some produce beneficial variations
Some negatively disrupt gene function.

42. Whether a mutation is negative or beneficial depends on how its DNA changes relative to the organism’s situation.
Mutations are often thought of as harmful because they disrupt the normal function of genes.
However, without mutations, organisms cannot evolve, because mutations are the source of genetic variability in a species.

43. Harmful effects
The defective proteins produced by these mutations can disrupt normal biological activities, and result in genetic disorders and cancers.

44. Beneficial effects
Mutations often produce proteins with new or altered functions that can be useful to organisms in different or changing environments.
Organisms can become resistant to certain pesticides and antibiotics.
Extra sets of chromosomes can be inherited which is called polyploidy.
Polyploid plants are often larger and stronger than diploid plants.