BIOL 2051 Lecture : JR - Ch. 7 Notes
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Chapter 7- Genomes and Chromosomes
Genetics
• Molecule of heredity
– Deoxyribonucleic acid (DNA)
• Gene
– Sequence of nucleotides in DNA that codes for a protein
• ONE gene codes for ONE protein
– Nucleotide sequence corresponds to sequence of amino acids
• RNA serves as an intermediate
The three key processes of macromolecular synthesis are:
(1) DNA replication – making a copy DNA
(2) transcription – synthesis of RNA from a DNA template
(3) translation – synthesis of proteins using messenger RNA as a template
Central dogma of molecular biology
• Basic processes are the same in prokaryotes & eukaryotes, but the organization of genetic
information is more complex in eukaryotes.
• Major differences:
Eukaryotes
- chromosomes are linear
- Introns- DNA sequences within genes that are not part of coding sequence for protein
- contain huge amount of noncoding DNA
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- In humans over 90% of the total DNA is noncoding (enhancer sequences,
promoters, gene remnants, pieces of viral genomes)
Prokaryotes
- Chromosomes are usually circular—vast majority of one singular, circular
chromosome
- have little non-coding DNA (less then 15%)
- Operons are common
- cluster of genes controlled by 1 regulatory sequence (or one promoter)
- genes are transcribed together into 1 mRNA strand then translated into
separate proteins
• DNA is a double-stranded helix (twisted ladder)
• The two strands in the double helix are antiparallel (run in opposite directions)
• The 2 DNA polynucleotide strands have base sequences that are complementary:
– Adenine pairs with thymine by 2 hydrogen bonds
– Guanine pairs with cytosine by 3 hydrogen bonds
• At the 5’ end is a phosphate group
• At the 3’ end is a hydroxyl group
• DNA is made of deoxyribonucleotides linked by phophodiester bonds
• Deoxyribonucleotide = sugar deoxyribose + nitrogenous base + phosphate
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• Nitrogen Bases: purines (adenine and guanine) and pyrimidines (cytosine and thymine)
• Attached to the 1’ C is the nitrogenous base
• The 5’ C is where the phosphate is located
• The 3’ C is attached to a hydroxyl group
• If another were to attach, the 5’ end would attach to the 3’ end.
• The phosphodiester bonds are in the backbone of DNA and cannot be broken.
Size of DNA
• Expressed as number of thousands of nucleotide bases or base pairs per molecule
• 1000 bases = 1 kb (kilobase) or 1kbp (kilobase pairs)
• Mycoplasma has smallest cellular genome known at 580 kbp. Mycoplasma depends on it host
for what it needs.
• Escherichia coli 4640 kbp
• Humans over 3.2 million kbp
• Nucleoid of E. coli- circle of dsDNA 1500X the size of the cell
• Can be packaged into the cell because it is supercoiled
• Topoisomerases assist in supercoiling
• DNA gyrase- type II topoisomerase introduces supercoiling by breaking and resealing the DNA
• Quinolone antibiotics such as ciprofloxacin target bacterial type II topoisomerase
• In addition to the chromosome, several other genetic elements exist in cells.
Document Summary
Sequence of nucleotides in dna that codes for a protein: one gene codes for one protein. Nucleotide sequence corresponds to sequence of amino acids: rna serves as an intermediate. The three key processes of macromolecular synthesis are: (1) dna replication making a copy dna (2) transcription synthesis of rna from a dna template (3) translation synthesis of proteins using messenger rna as a template. Central dogma of molecular biology: basic processes are the same in prokaryotes & eukaryotes, but the organization of genetic information is more complex in eukaryotes, major differences: Introns- dna sequences within genes that are not part of coding sequence for protein. In humans over 90% of the total dna is noncoding (enhancer sequences, promoters, gene remnants, pieces of viral genomes) Chromosomes are usually circular vast majority of one singular, circular chromosome. Have little non-coding dna (less then 15%) Cluster of genes controlled by 1 regulatory sequence (or one promoter)
