MBB 201 Lecture Notes - Lecture 9: Histone H2B, Mitosis, Nuclear Membrane
Chapter 5: DNA and Chromosomes
Most genetic information in DNA’s is for proteins
The Structure of DNA
Chromosomes
• Become visible as the cell starts to divide
• Contain both DNA and protein
DNA
• Deoxyribonucleic acid
• Contains only four types of nucleotides (Guanine, Cytosine, Thymine, Adenine)
• Nucleotides covalently bond together through sugar and phosphate- creating the
backbone
o Phosphodiester bond between phosphate and hydroxyl
• 5’ is the phosphate group, 3’ is the hydroxyl group
• Purine (double ring) (A, G)
• Pyrimidine (single ring) (T, C)
• Base pair- a purine bound to a pyrimidine
o GC, A=T
• 10 base pairs per helical turn
• Chargaff’s rule: A+G=T+C
o Since A=T and G=C
• Major and minor groves are common sites of DNA and protein interactions
• Junk DNA- function unknown
The Structure of the Eukaryotic Chromosome
Chromosomes
• DNA is packed tightly
• In bacteria chromosomes is circular
• DNA is distributed among multiple chromosomes
• Chromatin- complex of DNA and protein
• Contain two copies of each chromosome, one from the mother and one from the father
o Called homologous chromosomes
• Non-homologous chromosomes are the gender chromosomes
o Women have no Y chromosome
o Women inherit two X but no Y
• Karyotype- ordered display of all 46 chromosomes
Genes
• Functional unit of heredity
• Carried in chromosomes
• Segment of DNA containing instructions for a particular protein or RNA molecule
• Genome- total genetic information carried by a chromosome
• There may be a relationship between the complexity of the organism and the number of
genes it has
Cell Cycle
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Document Summary
Most genetic information in dna"s is for proteins. Chromosomes: become visible as the cell starts to divide, contain both dna and protein. Cell cycle: ordered events about the life time of a cell, growth and division. Interphase chromosomes are long and thin and easily tangled: each occupies a particular region, some attach to nuclear envelope or to nuclear lamina, replication origin- nucleotide sequence that exists in many parts of the. Proteins: proteins that bind to dna are, histone- large quantities, mass equal to about that of dna, non-histone chromosomal proteins, protein + dna is the chromatin. Beads on a string beads of nucleosome core particles on a string of dna: structure of the nucleosome determined by using nucleases to break phosphodiester bonds between nucleotides. Chromosome packing: h1 pulls adjacent nucleosomes together further packing them together, h1 is the linker histone (acts as clamp, changes the path dna takes as it exits the chromosome.