1. DNA and RNA Notes Part 2
Protein Synthesis

2. Genes and Proteins
Proteins form and become key cell structures and regulators of cell functions
Sequence of amino acid makes specific proteins
The sequence of nucleotides in each gene contains information for assembling amino acids.
It is estimated that each human cell contains about 80,000 genes

3. RNA
RNA – ribonucleic acid
4 Differences Between DNA and RNA
RNA DNA
Single Stranded Double Stranded
Sugar is Ribose Sugar is Deoxyribose
Adenine, Guanine, Adenine, Guanine, Cytosine, Uracil Cytosine, Thymine
RNA can leave the nucleus DNA can not leave nucleus

4. Instead of thymine, RNA uses uracil.
Notice that RNA is single-stranded instead of double-stranded.
-ose represents sugars and DNA and RNA both have different sugars.

5. DNA – A C G T G A A G C T G T A C A G T C A G G C T A
RNA – U G C A ……now do the rest your self remember Thymine is replaced with uracil in RNA!

6. What is the role of RNA in the cell:
DNA provides workers with the instructions for making the proteins
RNA takes the DNA instructions on how a protein is made then amino acid by amino acid they assemble the protein.
3 Types of RNA that help to build proteins
Messenger RNA (mRNA) – brings information from the DNA in the nucleus to the ribosome
Ribosomal RNA (rRNA) – what ribosomes are made of and they clamp onto the mRNA and use its information to assemble amino acids
Transfer RNA (tRNA) – transports amino acids to the ribosome to be assembled into a protein.

7. Transcription
Transcription – enzymes make an RNA copy of a portion of a DNA strand
The process of transcription is similar to replication except
Transcription results in single strand of RNA
Does not transcribe the entire strand of DNA

8. Steps of Transcription From DNA to RNA
The process of transcription begins as enzymes, RNA polymerase, unzips the molecule of DNA
As the DNA molecule unzips, RNA polymerase assembles RNA nucleotides using one strand of the DNA as a template.
Only the 3’  5’ template strand of DNA is transcribed. The RNA complimentary strand grows in the 5’  3’ direction.
Transcription continues until RNA polymerase reaches a special sequence of nucleotides.
mRNA molecule breaks away and mRNA leaves the nucleus and enters the cytoplasm.

10. The Genetic Code
Proteins are built from amino acids
20 different amino acids
Codon – each set of 3 nitrogen bases represents an amino acid, which is also called a triplet code
The order of nitrogen bases in DNA can determine the type and order of amino acids in a protein
64 different combinations
61 code for amino acids
3 signal to stop protein synthesis
More than 1 codon can code for the same amino acid

11. Codons represent the same amino acids in all organisms
Gives evidence of evolution
Start codon is AUG (methionine)
Stop codons are UAA, UAG, UGA

14. Translation From mRNA to Protein
Translation – the process of converting the information in a sequence of nitrogen bases in mRNA into a sequence of amino acids
Takes place at the ribosomes in the cytoplasm

15. The Role of Transfer RNA
To bring the amino acids to the ribosome
Correct translation of the mRNA message depends upon the joining of each mRNA codon with the correct tRNA molecule
tRNA recognizes the mRNA codon, because tRNA has a sequence of three nucleotides that are complement of the nucleotides in the codon
Anti-Codon – tRNA nucleotides
Ex: mRNA – A-C-A
tRNA – U-G-U

16. DNA – T–A–C–A–G –G –T–C–G –T–T–A–C–G–G–A–C–T
mRNA –
tRNA –
Amino Acids

18. Translating the mRNA Code
Steps of Translation
The first codon of the mRNA strand attaches to a ribosome
tRNA molecules, each carrying a specific amino acid approach the ribosome
tRNA anticodon pairs with mRNA codon
The first codon on mRNA is AUG which codes for amino acid methionine. AUG is the start codon for protein synthesis
A new tRNA molecule carrying an amino acid will pair with the mRNA codon
As the process continues a chain of amino acids is formed until the ribosome reaches a stop codon on the mRNA strand UAA, UAG, UGA

22. 12-4 Mutations
Mutation: A Change in DNA
Mutation – any change in the DNA sequence that also changes the protein it codes for
Mutations in Reproductive Cells
If mutation occurs in egg or sperm the altered gene would become part of the genetic makeup of the offspring
Sometimes the mutation is so severe that the embryo does not survive
In rare cases a gene mutation may have positive effects

23. Mutations in Body Cells
If the cells DNA is changed this mutation would not be passed on to offspring
But the mutations can cause harm to the individual

24. 2 Types of Mutations in DNA
Point Mutation
Is a change in a single base pair in DNA
A change in a single letter changes the meaning of this sentence
2. Frameshift Mutation
A mutation in which a single base is added or deleted from DNA
This mutation would cause nearly every amino acid in the protein after the deletion to be changed.

26. Chromosomal Mutations
Chromosomal Mutations – changes in chromosomes during replication. Parts can be broken or lost.
They occur in all living organisms, but they are especially common in plants
Although rare, changes in an organisms chromosome structure do occur.
Chromosomal mutations are rarely passed on to the next generation because:
The zygote usually dies
The mature organism is usually sterile

27. 4 Types of Chromosomal Mutations
Deletion – a fragment of a chromosome breaks off, it can be lost when a cell divides

28. 2. Duplication – the chromosome fragment attaches to its homologous chromosome, which will then carry two copies of a certain set of genes

29. 3. Inversion – fragment reattaches to the original chromosome in the reverse orientation

30. 4. Translocation – a fragment may join a nonhomologous chromosome

31. Causes of Mutations
Spontaneous Mutations – a mistake in base pairing during DNA replication. It occurs at random or at any given moment
Mutagen – any agent that can cause a change in DNA
Ex. Chemicals, radiation, high temperatures

32. Repairing DNA
When mistakes do occur repair mechanisms fix mutations
Proofreading Enzymes – reads the DNA strand and checks it for mistakes
Repair Enzymes – fixes any mistakes in the DNA strand

33. Mistakes in Meiosis
Sometimes accidents occur during meiosis and chromosomes fail to separate correctly
Nondisjunction – failure of homologous chromosomes to separate
During meiosis I one chromosome from each pair is supposed to move to opposite poles but occasionally both chromosomes of a pair move to the same pole

34. Trisomy – 1 extra chromosome (47)
Ex: extra chromosome on pair number 21 – down syndrome
Monosomy – missing 1 chromosome (45)
Ex: missing chromosome on pair number 23 – turner syndrome
Tetraploid – 2 extra chromosomes (48)
Polyploids – organisms with more than the usual number of chromosome sets
Is rare in animals and almost always results in death.