U2L10 Flashcards
State the nitrogenous bases of a DNA strand
Thymine, Guanine, Cytosine, Adenine
Uracil - only in RNA
What is attached to a deoxyribose sugar?
Phosphate group and Nitrogenous base
What backbone does a DNA strand have?
Sugar phosphate
What did Rosalind Franklin and Maurice Wilkins do?
Used X-ray crystallography to produce a picture of the DNA molecule
How did the Xray images help Watson?
- Helped him conclude the DNA is helical
- Helped him calculate the width of the helical and the space between nitrogenous bases
- The photo suggested that DNA molecules formed a double helix
What are phosphate groups attached to?
5’ ends
What do covalent sugar phosphate bonds link?
Nucleotides of each strand
What holds nitrogenous bases together?
Hydrogen bonds
What did Watson and Crick do?
Build models of a double helix
Watson built a model where backbones were antiparallel (run in opposite directions)
What did Watson determine?
That adenine pairs with Thymine and guanine pairs with cytosine
Chargaff’s rule
A=T
G=C
Species A has 4 million GC pairs and 2 million AT pairs.
Species B has 4 million AT pairs and 2 million GC pairs.
Which do you think can live at higher temperature? Why?
Species A because GC forms 3 hydrogen bonds whereas AT forms 2 hydrogen bonds. It takes energy to break down more hydrogen bonds so species A will be more resistant to higher temperatures
List some of the proteins involved in the initiation of DNA replication
Topoisomerase, primase, helicase, single strand binding proteins
What does topoisomerase do?
Prevents DNA from getting tangled and relives pressure - unwinds DNA
How many types of DNA polymerase are there and what do they do?
2 types - DNA polymerase 2 and 3 - add correct nucleotides
How does antiparallel structure affect replication
DNA polymerase adds nucleotides only to the free 3’ end of a growing strand, therefore a new DNA strand can elongate only in 5’ to 3’
Which way does a leading strand move?
Towards the replication fork
How is the lagging strand elongated?
DNA polymerase must work in the direction away from the replication fork. The lagging strand is synthesized as series of segments called Okazaki fragments which are joined by DNA ligase
What does helicase do?
Unwinds the parental double helix
What happens if nucleotides are not placed in the right spot?
Repair enzymes correct errors in base pairing
What happens in a nucleotide excision repair?
A nuclease cuts out and replaces damaged stretches of DNA
What is the evolutionary significance of altered DNA nucleotides
changes in sequence have chances of being permanent and can be passed down to the next generation - these changes (mutations) are sources of genetic variation upon which natural selection operates
What are telomeres?
Eukaryotic chromosomal DNA molecules have special nucleotide sequences at their ends called telomeres
What does repeated rounds of replication produce?
Shorter DNA molecules with uneven ends
What do telomeres postpone?
The erosion of genes near the ends of chromosomes - shortening of telomeres is connected to aging
What does telomerase do?
Catalyzes lengthening of telomeres in germ cells
How can the shortening of telomeres be a good thing?
Might protect cells from cancerous growth by limiting the number of cell divisions
Describe DNA molecules in bacteria and eukaryotic
Bacterial chromosomes are double stranded - circular DNA molecules with small amounts of protein
In a bacterium - DNA is supercoiled and found in nucleoid
Eukaryotic chromosomes are linear DNA molecules with large amounts of protein
What is chromatin?
Complex of DNA and protein found in nucleus of eukaryotic cells
Inheritance of Tay Sachs disease
Autosomal recessive
Inheritance of cystic fibrosis
Autosomal recessive
Inheritance of sickle cell anemia
Autosomal recessive
Inheritance of Achondroplasia
Autosomal dominant
Inheritance of hemophilia
X linked recessive
Inheritance of colour blindness
X linked recessive
