Nucleic acids and chromosomes Flashcards Preview

MCD - Nucleic Acids and Gene Expression > Nucleic acids and chromosomes > Flashcards

Flashcards in Nucleic acids and chromosomes Deck (25):
1

Components of nucleotides

Base, sugar, phosphate

2

Components of nucleosides

Base, sugar, no phosphate

3

Structure of DNA/RNA

Chain of nucleotides linked by phosphodiester bonds
3' OH of sugar linked to phosphate group attached to 5' carbon of next nucleotide
First nucleotide in sequence has free phosphate attached to 5' carbon
Last nucleotide in sequence has a free hydroxyl group attached to the 3' carbon.

4

Direction of DNA/RNA writing

5' end to 3' end

5

Features of the double helix

- 10 base pairs per helical turn
- Major and minor grooves
- Hydrogen bonds between bases on the two strands give helix stability
- Chains are antiparallel (they run in opposite directions)
- Negative charges on phosphate group make the sugar-phosphate backbone run on the outside with the bases on the inside.

6

DNA bases

Adenine
Thymine
Cytosine
Guanine

7

RNA bases

Adenine
Uracil
Cytosine
Guanine

8

Purine bases

Adenine
Guanine

9

Pyrimidine bases

Thymine
Cytosine
Uracil

10

Difference between purine and pyrimidine

Purine = double ring
Pyrimidine = single ring

11

Watson-Crick base pairs

- Adenine with Thymine/Uracil = forms two H bonds between bases
Cytosine with Guanine = forms three H bonds between bases

12

Conditions used for denaturing/melting (separation) of strands

Heat
Low salt

13

Conditions used for re-annealing of strands

Cool
High salt

14

Process of hybridisation in NA analysis

- Target DNA from agar plate/gel immobilised on solid support
- DNA then readily binds single-stranded nucleic acid (denatured DNA/RNA)
- Hybridised with solution of radioactively or fluorescently labelled probe

15

What is hybridisation

A method for detecting specific nucleic acid sequences, homologous single-single stranded DNA/RNA molecules combine to form double-stranded molecules. Probe used to show sequence presence.

16

What is PCR

Polymerase Chain Reaction, an in vitro (outside of the cell) method which allows the selective amplification of a specific target DNA within a mixed collection of DNA sequences.

17

Process of PCR

- 2 primers designed to be complementary to target sequences
- Primers annealed to denatured DNA by lowering the temperature
- TAQ polymerase and free nucleotides (dNTPs) extend the chain
- Denature and repeat the cycle several times to generate many copies of target DNA

18

Temperatures for denaturing, annealing, and extension in PCR

- Denaturing = 94 degrees
- Annealing = 50-60 degrees
- Extension = 72 degrees

19

What types of restriction enzymes are used and what do they do

Type 2 restriction endonucleases which cleave the DNA at specific recognition sequences

20

What types of ends do restriction enzymes produce and what is the difference between them

Blunt ends - both strands cut at the same nucleotide.
Sticky ends - Each strand cut at different nucleotides, two nucleotides apart. Ends overlap.

21

Association between recognition site length and occurrence frequency in DNA

The longer the recognition sequence, the less frequently it occurs in DNA

22

What is a nucleosome

Structural unit of human chromosomes, consists of length of DNA coiled around a core of histones.

23

Packaging of DNA

DNA wrapped around histone proteins. These are positive proteins which interact with negative phosphates on the DNA. 10000 fold shortening due to histones.

24

What is a karyotype

An organised profile of a person's chromosomes

25

What is the normal human karyotype

A diploid human has 22 autosomal chromosome pairs and one sex-determining chromosome pair