Lecture 1&3 - Chapter 9
Stable DNA structure is ideal for storing genetic information
- Supercoiling is controlled by topoisomerases
- Eukaryotic DNA is supercoiled.
o Aids in chromatin packaging
- Histone proteins
o Major histone types:
H1, H2a, H2b, H3, H4
o Conserved proteins
o Arginine and Lysine - abundant - interact with negatively charged phosphate
groups in DNA
o Structural role in chromatin
Protease degrades proteins
1 - Adenine and Thymine form two hydrogen bonds
- Guanine and Cytosine form three hydrogen bonds.
Supercoils are introduced into a DNA molecule when one or both strands are cleaved and when
the complementary strands at one end are rotated or twisted around each other with the other end
held fixed in space—and thus not allowed to spin.
Chromosomes contain chromatin
- Chemical analysis of isolated chromatin shows that it consists primarily of DNA and
proteins with lesser amounts of RNA
- The proteins are of two major
o (1) Basic (positively charged at neutral pH) proteins called histones
o (2) A
heterogeneous, largely acidic (negatively charged at neutral pH) group of proteins
collectively referred to as nonhistone chromosomal proteins.
- Histones play a major structural role in chromatin.
- Four of the five types of histones are specifically complexed with DNA to produce the basic
structural subunits of chromatin, small ellipsoidal beads called nucleosomes.
Telomeres end of eukaryotic chromosome
- 1. Prevent deoxyribonucleases from degrading the ends of the linear DNA molecules,
- 2. Prevent fusion of the ends with other DNA molecules
- 3. Facilitate replication of the ends of the linear DNA molecules without loss of material.
- Shorten with age (except for cancer ones)
- Telomers of humans form structures called T-loops
- DNA in T-loops protected by a protein complex called shelterin
2 Lecture 4&6 - Chapter 10
3 DNA Replication in Eukaryotes
• Shorter RNA primers and Okazaki fragments
• DNA replication only during S phase
• Multiple origins of replication
RNA primer made of primase -- synthizes short RNA primer made of nucleotides.
role --> to put down a primer, one on a leading strand and multiple on the lagging strand to
make replication happen.
3'OH to start replication
4 Lecture 7&10 - Chapter 11
Gene expression in Eukaryotes
- Genes are interrupted 2 exons separated by an intron (intervening sequence)
--> Main difference from prokaryotes/genes can be very complex; most genes have
multiples exons and multiple introns
- PreMRNA - Pre Messenger RNA
- Called pre because it contains the exons and the introns
- Introns are not protein-contained sequence; cells get rid of them.
- Processing of MRNA, addition of cap, MG,
- Poly A tail, adds A residues
- Ribosome, translation machinery, recognizes it and makes it into proteins transcription
occurs in nucleus, and translation occurs in cytoplasm
Links mRNA to protein synthesis
involved in translation, makes up protein translating machine
• RNA/protein structure
• Five snRNAs: U1, U2, U4,
U5, and U6
• The snRNAs associate with
proteins to form snRNPs
6 Lecture 10 & 12- Chapter 12
Protein Synthesis: Translation
- The process by which the genetic information stored in
the sequence of nucleotides in an
mRNA is translated, according to the specifications of the genetic code, into
of amino acids in the polypeptide gene.
- The first step in gene expression, transcription, involves the transfer of information
stored in genes to messenger RNA (mRNA) intermediaries, which carry that
information to the sites of polypeptide synthesis in the cytoplasm.
- The second step, translation, involves the transfer of the information in mRNA molecules
into the sequence of amino acids in polypeptide gene products.
o Occurs on ribosomes
1. Polypeptide Chain Initiation
o The initiation of translation includes all events that precede the formation of a peptide bond
between the first two amino acids of the new polypeptide chain.
o AUG initiation codon
2. Polypeptide Chain Elongation
3. Polypeptide Chain Termination
- Polypeptide chain elongation undergoes t