1. Chap. 4—Genetics and Cellular Function

2. Ch. 4 Study Guide
Critically read Chapter 4 up to page 129 right before 4.3 “DNA Replication and the Cell Cycle” section
Comprehend Terminology (those in bold in the textbook)
Study-- Figure questions, Think About It questions, and Before You Go On (section-ending) questions
Do end-of-chapter questions:
Testing Your Recall— 2, 4, 5, 6, 7, 18
True or False– 1, 2, 4-7 2

3. § 4.1 DNA and RNA– The Nucleic Acids

4. § DNA structure (1) General Molecular level—
DNA– deoxyribonucleic acid
Most human cells have 46 molecules of DNA
A uniform diameter of 2 nm and the average 2-in.
Molecular level—
Nucleic acids (DNA + RNA) are polymers of __________________________
A nucleotide consists of (1) ________ + (2) ________ + (3) ___________________
DNA is a double helix spiral staircase)
Fig. 4.1 a +b and 4.2

5. A nucleotide consists of three components
Adenine
See next slide
A nucleotide consists of three components
NH2 C N C N HC CH C N N H O HO P O
CH2 O OH H H H H OH H
Phosphate
Deoxyribose
(a)

6. Five nitrogenous bases:
Purines
NH2 N C H C C CH C C HN C NH N C NH C N C N H
NH2
Adenine (A)
Guanine (G)
Pyrimidines
NH2
CH3 O H C C C C H C N HC NH N C N C H H O O
Cytosine (C)
Thymine (T)
T: Only in DNA O C H N C H C C H N O H
Uracil (U)
U: Only in RNA
(b)

7. § DNA Structure (2)
Space-filling model
“Twisted ladder”

8. § DNA Structure (3)
DNA = a double helix molecule; a spiral staircase; a soft rubber ladder that you can twist
Details:
Each sidepiece is a backbone-- composed of phosphate groups alternating with the sugar deoxyribose.
Step-like connections-- between the backbones are pairs of nitrogenous bases.
The arrangement of these nitrogenous bases– How? (Next slide)

9. § DNA Structure (4) Law of complementary base pairing:
Sugar-phosphate backbone
Law of complementary base pairing:
Base pairs (2 kinds):
A-T and C-G
Nitrogenous bases form hydrogen bonds
Segment of DNA

10. § DNA Function Carry instructions of genes for protein synthesis
A gene – a segment of DNA that codes for one polypeptide (or closely related proteins)
Genes determine the characteristics of a species and each individual
Genome - all the genes of one person
humans have estimated 25,000-35,000 genes (2% of DNA)
The other 98% of DNA is noncoding – either “junk” or organizational DNA

11. Think About It
What would be the base sequence of the DNA strand across from ATTGACTCG?
If a DNA molecule were known to be 20% adenine, predict its percentage of cytosine.

12. § Chromatin and Chromosomes
Chromatin—filamentous material making up 46 chromosomes (DNA and proteins) in the interphase nucleus
Chromatin appears like “beads on a string” packed together (Fig. 4.2 a-f)
The beaded string is divided into segments called nucleosomes (consist of histones and linker DNA)
In dividing cells, DNA coils and supercoils itself to form chromosomes (can be seen with light microscope) . Fig. 4.5

13. 2 nm 1
DNA double
helix

14. DNA winds around core particles Core particle Linker DNA 11 nm 2
Nucleosome

15. 30 nm 3
Nucleosomes
Fold into zigzag
fiber

16. 300 nm 4
fiber is
thrown into
irregular loops

17. looped chromatin coils further into a chromatid In dividing cells only
700 nm 5
looped
chromatin coils
further into a
chromatid

18. Chromosome at the midpoint (metaphase) of cell division Chromatids
Centromere
700 nm 6
Chromosome
at the midpoint
(metaphase) of
cell division

19. Chromosome structure at metaphase
Kinetochore
Centromere
Sister
chromatids
(a)

20. § RNA (ribonucleic acids): Structure
RNA-- much smaller than DNA (fewer bases)
messenger RNA (mRNA) has over 10,000 bases
ribosomal RNA (rRNA)
transfer RNA (tRNA), smallest, has bases (Fig. 4.8)
Are these bases (of RNAs) paired or unpaired?
Only one nucleotide chain (not a double helix)
ribose replaces deoxyribose as the sugar
uracil replaces thymine as a nitrogenous base

21. Figure 4.8
Transfer RNA (tRNA)

22. § RNA: Function
DNA directs the synthesis of proteins by means of its smaller cousins, the RNAs
Essential function of RNA--
interpret DNA code
direct protein synthesis in the cytoplasm
(Location) RNA works mainly in the cytoplasm while DNA remains safely behind in the nucleus
Table 4.1 is an excellent summary (Comparison of DNA/RNA)

23. Check Point Questions
What are four nitrogenous bases found in RNA? a) U, G, C, T; b) A, G, C, T c) A, U, G, C; d) A, T, G, C
In RNA, when does the secondary structure called a hairpin form?
When hydrophilic residues act with water
When complementary base pairing between ribonucleotides on the same strand creates a stem-and-loop structure
When complementary base pairing forms a double helix

24. § 4.2 Genes and Their Action

25. § Protein Synthesis: Genetic Control of Cell Action
DNA codes for the synthesis of all cell proteins
including enzymes that direct the synthesis of nonproteins
For example, Testosterone production
Different cells synthesize different proteins
Why?
Due to differing gene activation
See Fig (next slide)

26. = LH

27. § Summary of Protein Synthesis
DNA contains a genetic code that specifies which proteins a cell can make; protein synthesis as: DNA  mRNA  protein
Transcription (DNA  mRNA); What? Details?
messenger RNA (mRNA) is formed next to an activated gene
mRNA migrates to cytoplasm
Translation (mRNA  protein) (Fig. 4.7) What? How?
mRNA code is “read” by ribosomes
transfer RNA (tRNA) delivers the amino acids to the ribosome
Ribosomes assemble amino acids in the order . . .

28. § Genetic Code
Def. -- System that enables the 4 nucleotides (A,T,G,C) to code for the 20 amino acids
Base triplet: (of DNA) Fig. 4.10
Def.– A sequence of 3 nucleotides that stand for 1 amino acid
found on DNA molecule (ex. TAC codes for AUG in mRNA)
Codon: (genetic code is expressed in terms of codons)
Def.--“mirror-image” sequence of nucleotides found in mRNA (ex. AUG is the codon of mRNA, code for methionine, an amino acid) (Table 4.2)
64 possible codons (43)
often 2-3 codons represent the same amino acid
start codon = AUG
3 stop codons = UAG, UGA, UAA

29. A
Seven base triplets B

31. § Protein Synthesis (details)
Three sites of the large subunit of ribosome:
P (peptidyl) site—
A (acceptor) site—
E (exit) site--

39. Watch a video-- An animation: protein synthesis, when available