1. DNA, RNA and Protein Synthesis
TAKS Review
Spring 2012

2. Structure of DNA DNA is deoxyribonucleic acid
DNA is a large molecule that has subunits called nucleotides.
The nucleotides come together to make the DNA molecule in the shape of a double helix (looks like a twisted ladder).

3. Nucleotides
Nucleotides are the subunits that make up DNA and they have 3 major parts:
A sugar molecule (deoxyribose sugar)
A phosphate group
A nitrogen base

4. Nitrogen bases There are 4 kinds of nitrogen bases: Adenine (A)
Guanine (G)
Thymine (T)
Cytosine (C)

5. DNA Structure DNA is a double helix (twisted ladder)
The handrails of the ladder are made of phosphate and sugar
The rungs of the ladder are made of nitrogen bases.

6. Bonding
Sugar and phosphate bond using covalent bonds (strong) and nitrogen bases bond using hydrogen bonds (weak)
Nitrogen bases are specific: Adenine (A) always attaches to Thymine (T); and Cytosine (C) always attaches to Guanine (G)
(Think apples in trees, cars in garages)

7. DNA Replication A review:
A cell will make an exact copy of itself during a process called mitosis
Before the cell can copy itself it must copy all of it’s DNA so that both daughter cells have the same number of chromosomes.

9. DNA replication takes place in 3 steps
1. DNA unwinds at the hydrogen bonds
2. nucleotides are added to the exposed nitrogen bases. It follows base pairing rules. (A –T and C-G)
3. The DNA winds back up producing 2 new strands.

10. What’s the complementary strand?
If one side is CAG, what is the complementary strand?
Answer: GTC
If one side is AAC, what is the complementary strand?
Answer: TTG

11. RNA vs DNA Characteristic RNA DNA Strands 1 2 Sugar molecule Ribose
Deoxyribose
Bases
A, U, C, G
A, T, C, G
Found
Nucleus and cytoplasm
Nucleus only
Building block
Nucleotide

12. Kinds of RNA
There is only one kind of DNA, but there are 3 kinds of RNA.
Messenger RNA (mRNA)
Transfer RNA (tRNA)
Ribosomal RNA (rRNA)

13. Gene Expression DNA (double-stranded) Transcription
RNA (single-stranded)
Translation
Protein (amino acid chain)

14. Central Dogma of Molecular Biology

15. Transcription= taking DNA and making an RNA copy of it
Transcription= taking DNA and making an RNA copy of it. Uses complementary nucleotides. C=G, G=C, T=A, A=U

16. The Genetic Code
Remember that messenger RNA – mRNA- is a copy of the DNA. It carries instructions for making a protein.
The instructions (nucleotides) have to be translated into proteins (amino acids).
A sequence of three nucleotides is called a codon, and it corresponds to an amino acid.
We use a codon chart for translation

18. Genetic Mutations

19. Mutation A mutation is any change in a genetic code (DNA).
It may not change the resulting amino acid chain and is called a silent mutation
EXAMPLE: Notice how the resulting a.a. sequence is the same in spite of the change:
Original DNA: CAA CCC AAA
Resulting mRNA: GUU GGG UUU
Resulting amino acid: Val – Gly - Phe
Mutated DNA: CAA CCC AAG
Resulting mRNA GUU GGG UUC
Resulting amino acid: Val – Gly – Phe

20. Point Mutation or Substitution Mutation
A point mutation is a change in one nucleotide. It can be silent or it can cause a change in one amino acid
Can be devestating if the resulting amino acid has a STOP codon inserted as a result
Original DNA: ATG CCC AAA
Resulting mRNA: UAC GGG UUU
Resulting amino acid: Tyr – Gly - Phe
Mutated DNA: ATG ACC AAA
Resulting mRNA UAC UGG UUU
Resulting amino acid: Tyr – Trp – Phe
Mutated DNA: ATT CCC AAA
Resulting mRNA: UAA GGG UUU
Resulting amino acid: Stop

21. Insertion and Deletion Mutations
Insertion – addition of one or more nucleotides
Deletion – deletion of one or more nucleotides
Insertion and deletion mutations are almost always devastating because it will cause a frame-shift to occur.
Imagine if a sentence of 3-letter words lost a letter?
Original sentence: The cat and dog are fat.
A mutation occurs that deletes the c in cat.
Mutated sentence: Thc ata ndd oga ref at.
The same things happen to DNA when it mutates

22. Frame Shift Mutation Original DNA: CAT AGC TAG GAT
Resulting mRNA: GUA UCG AUC CUA
Resulting amino acid: Val–Ser-Ile-Leu
Mutated DNA: CAA GCT AGG AT
Resulting mRNA: GUU CGA UCC UA
Resulting amino acid: Val-Arg-Ser-?

23. Mendel’s Theory and Studying Heredity

24. The Flower

25. Mendelian Theory of Heredity
2 sets of chromosomes = 2 copies of each gene
Alleles—alternative forms of a gene
Purple vs. white flowers
Dominant allele—trait that is expressed or seen.
Recessive allele—trait that is not seen. To be seen, must be present in 2 copies.

26. Terms and Notations Dominant alleles = capital letters
Recessive alleles = lower case letters
Dominant allele is always written first
Homozygous individual—alleles are the same (EX: PP or pp)
Heterozygous individual—alleles are different (EX: Pp)

27. Terms and Notations Continued
Genotype—set of alleles, or genes.
Phenotype—physical appearance of a trait.
Genotype Phenotype
PP purple flowers, homozygous dominant
Pp purple flowers, heterozygous
pp white flowers, homozygous recessive

28. Punnett Squares Diagram that predicts the outcome of a genetic cross
Top represents one parent, side the other
Letters in the box indicate the possible genotypes of the offspring.

29. Example Punnett Square
¼=YY homozygous dominant
2/4=Yy heterozygous
¼=yy homozygous recessive
Yy—heterozygote Y y Y YY Yy
Yy—heterozygote y Yy yy

30. Inheritance of Traits
Pedigree—family history that shows how a trait is inherited over several generations.
Helps identify carriers of genetic disorders
Carriers—individuals who are heterozygous for a genetic disorder but do not show symptoms—can pass the mutant allele to their offspring

31. Example Pedigree
Male
Male with disorder
Female
Female with disorder