DNA structure

Question 1

Describe the structure of DNA nucleotides

Answer 1

-deoxyribose
-phosphate (usually 3 when in cell) on 5’ carbon
-base on 1’ carbon

Question 2

What are the 2 types of base?

Answer 2

Purines - adenine and guanine (2 carbon rings)
Pyrimidines - cytosine and thymine (1 carbon ring)

Question 3

Which bases pair together and how many bonds do they form?

Answer 3

A-T form 2 hydrogen bonds
G-C form 3 hydrogen bonds

Question 4

How do 2 adjacent nucleotides join together?

Answer 4

OH group on 3’ carbon forms phosphodiester bond with phosphate on 5’ carbon of adjacent, releasing water

Question 5

What was Chargaff’s’ experiment and what did he conclude?

Answer 5

-used paper chromatography to separate + isolate nucleobases components of DNA from different species
-compared ratios of the bases to each other
-%A=%T and %G=%C
-%AT=/=%CG

Question 6

What were the conclusion from Wilkins and Franklin’s experiment?

Answer 6

-X pattern shows it has a helical structure
-regular pattern shows that it has a repeating, even structure
-distance between spots = distance of one turn

Question 7

What are the main features of the Watson and Crick model?

Answer 7

-AT and GC H bonded base pairs
-antiparallel, complementary strands
-right handed double helix
-major + minor groove in DNA double helix

Question 8

What are chromosomes?

Answer 8

Long DNA molecules with all or part of the genetic material of an organism

Question 9

Describe eukaryotic chromosomes

Answer 9

-linear molecules held in the nucleus
-often have many chromosomes per genome
-contain centromeres + telomeres

Question 10

What are centromeres and what do they do?

Answer 10

-specialised chromosomal region in which the structures that link to spindle microtubules assemble
-help chromosomes segregate at mitosis + meiosis

Question 11

Describe how genetic material is found in prokaryotes

Answer 11

-bacteria generally have a single, circular chromosome
-plasmids are also often found (circular)

Question 11

What are the roles of DNA binding proteins?

Answer 11

-regulate gene expression
-cut DNA at specific sequences
-protect DNA

Question 11

Describe histones

Answer 11

-eukaryotic genomes are packaged into chromatin
-DNA wrapped around histone proteins
-not sequence specific

Question 11

What are telomeres and what do they do?

Answer 11

-repetitive DNA at the ends of linear chromosomes
-protect the ends of linear chromosomes

Question 11

Describe restriction endonucleases

Answer 11

-enzymes that cut DNA at specific (normally palindromic) sequences
-viral DNA is cut by enzyme but bacterial DNA is protected as it’s methylated

Question 12

Describe transcriptional regulators

Answer 12

-proteins that bind to regulatory sequences near the promoters of genes
-stimulate or block transcription
-bend DNA into favourable or unfavourable shape