Genetics Module 9, The Chemical Nature of the Gene
Characteristics of genetic material
Stores information, replicates, encodes phenotypes and has the capacity to very
A repeating unit of DNA or RNA made up of a five pentose sugar, phosphate and a nitrogenous base
Nucleotides
Rules developed concerning the ratios of bases in DNA
Chargaffs rules
Substance responsible for transformation; now known to be DNA
Transforming principle
Purines
Large double ringed bases adenine and guanine
Pyrimidine
Smaller single ringed bases thymine, cytosine and uracil
Ribose or deoxyribose bonded to a nitorgenous base
Nucleoside
A phosphorus atom bonded to four oxygen atoms; one of three components of a nucleotide
Phosphate group
Building block of DNA; consists of deoxyribose, a phosphate group and a nitrogenous base
Deoxyribonucleotide
Building block of RNA; consists of ribose, a phosphate group and a nitrogenous base
Ribonucleotide
A strong covalent bond that joins the 5’-phosphate group of one nucleotide to the 3’-hydroxyl group of the next nucleotide in a polynucleotide strand
Phosphodiester Linkage
Series of nucleotides linked together by phosphodiester bonds
Polynulceotide strand
End of a polynucleotide chain at which a phosphate group is attached to the 5’-carbon atom of the sugar in the nucleotide
5' end
End of a polynucleotide chain at which an OH group is attached to the 3’-carbon atom of the sugar in the nucleotide
3' end
A DNA molecule is made up of two linked strands that wind around each other to resemble a twisted ladder in a helix-like shape. Each strand has a backbone made of alternating sugar and phosphate groups and the two stands are connected by hydrogen bonds between the nitrogenous bases
DNA double helix
The orientation of the two polynucleotide strands of the DNA double helix in opposite directions
Anti-parallel
Nucleotide strands of DNA in which each purine on one strand pairs with a specific pyrimidine on the opposite strand (A pairs with T, and G pairs with C)
Complementary DNA strands
Concept that genetic information passes from DNA to protein in a one-way information pathway
Central dogma
Process by which RNA is synthesized from a DNA template
Transcription
Process by which a protein is assembled from information contained in mRNA
Translation
Process by which DNA is synthesized from a single-stranded nucleotide template
Replication
Tertiary structure that forms when strain is placed on a DNA helix by overrotation or underrotation
Supercoiling
Energy state of a DNA molecule when there is no structural strain on the molecule
Relaxed state of DNA
A circular chromosome found in the nucleoid whereby there are no free ends to the DNA
Bacterial chromosome
Linear chromosome found in the nucleus whereby DNA is tightly wound around clusters of histone proteins
Eukaryotic chromosome
Enzyme that adds or removes rotations in a DNA helix by temporarily breaking nucleotide strands; controls the degree of DNA supercoiling
Topoisomerase
Bacterial DNA confined to a definite region of the cytoplasm
Nucleoid
Chromatin that undergoes the normal process of condensation and decondensation in the course of the cell cycle
Euchromatin
Low-molecular-weight protein found in eukaryotes that associates closely with DNA to form chromosomes
Histone
Basic repeating unit of chromatin, consisting of a core of eight histone proteins and DNA that wraps around the core about two times
Nucleosome
Stretch of DNA separating two nucleosomes
Linker DNA
Chromatin that remains in a highly condensed state throughout the cell cycle; found at the centromeres and telomeres of most chromosomes
Heterochromatin
Higher level DNA supercoiling that consists of a helical array of nucleosomes in chromatin
30-nm fiber
Higher level DNA supercoiling whereby the 30-nanometer chromatin fiber forms loops averaging 300 nanometers in length
300-nm loops
The 300 nm fibers in chromatin are compressed and folded to produce a 250 nm-wide fiber, which is tightly coiled into the chromatid of a chromosome
250-nm fiber
Sequence found at the ends of a chromosome; consists of many copies of short, simple sequences repeated one after the other
Telomeric sequence
Amount of DNA per cell in an organism
C-Value
DNA sequence that is present only once or, at most, a few times in the genome
Unique Sequence DNA
Multiprotein complex that binds to telomeres and protects the ends of the DNA from being inadvertently repaired as a double-stranded break in the DNA
Shelterin
DNA that consists of short sequences that are present in hundreds of thousands to millions of copies that are repeated in tandem and are clustered in certain regions of chromosomes
Highly repetive DNA
Type of moderately repetitive DNA in which sequences are repeated one after another; tend to be clustered at specific locations on a chromosome
Tandem repeat sequence
A major class of repetitive DNA, which typically consists of sequences from 150 to 300 bp in length that are repeated thousands of times
Moderatley repetitive DNA sequence
Repeated sequences that are scattered throughout the genome
Interspersed repeated sequences
DNA sequences that exist in multiple copies in a genome
Repetitive DNA
How do the sugars of DNA and RNA differ?
The sugar of RNA has a hydroxyl group not found in the sugar of DNA
The anti-parallel nature of DNA refers too what?
The opposite direction of the two strands of nucleotides
How does Z DNA differ from B DNA?
Z-DNA has a left-handed helix; B-DNA has a right-handed helix. The sugar-phosphate backbone of Z-DNA zigzags back and forth, whereas the sugar-phosphate backbone of B-DNA forms a smooth continuous ribbon.
How many complete rotations should DNA have per base pair?
Ten base pairs per complete rotation
A DNA molecule 300 bp long has 20 complete rotations. This DNA molecule is what?
Negativley supercoiled
How does bacterial DNA differ from eukaryotic DNA?
Bacterial DNA is not complexed with histone proteins and is circular
Neutralizing their positive charges would have which effect on the histone proteins?
They would bind less tightly to the DNA
Characteristics of DNA at the telomeres
- Consist of repeated sequences
- One strand protrudes beyond the other, creating some single-stranded DNA at the end
- One strand consists of guanine and adenine (or thymine) nucleotides
Most of the genes at encode DNA are found in what type of DNA?
Unique-sequence DNA
What is NOT a component of a nucleotide found in RNA?
Thymine
Which is true of the secondary structure of DNA?
The paired nucleotide strands are anti-parallel
What would happen to a linear DNA molecule that lacks a telomere end?
It would be unstable and degrade
In humans, 20% of bases in DNA are cytosine (C). What percentage of the bases are expected to be thymine (T)?
30%
If a double-stranded DNA molecule has 15% thymine, what are the percentages of all the other bases?
A: 15%
C: 35%
G: 35%
Shorter more compact version of B-DNA with a right handed structure that usually exists when there is a lack of water present
A-DNA
The most common and stable form of DNA with a right handed structure
B-DNA
DNA with a left handed structure. Is formed through environmental factors including alternating purine-pyrimidine sequences and negative supercoiling.
Z-DNA