MFM Week 2 Nucleic Acids and Genetic Code

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1

Detail pyrimidines

Heterocyclic aromatic containing 2 nitrogen atoms and are weakly basic
Cytosine
Thymine

2

Detail purines

Heterocyclic aromatic organic compound consisting of a pyrimidine ring fused to an imidazole ring and are weakly basic
Adenin
Guanine

3

Nucleoside

Contains a nitrogenous base and sugar (no phosphate)

4

Nucleotide

Contains all three components - nitrogenous base, sugar, and phosphate

5

How is the backbone of DNA linked

Through a phosphate backbone through phosphodiester bonds, with a 3'carbon of one sugar linked to the 5'carbon of the next sugar. DNA has a negative charge due to free O- at physio. pH

6

Base pairing

T=A is 2 hydrogens
C-=G is 3 hydrogens

7

Detail DNA strands

Antiparallel - one strand is oriented 5'->3' direction (5 carbon of sugar) while other is 3'->5'. There are grooves in the double helix so that proteins can interact with the DNA

8

What stabilizes DNA

Van der walls interactions, hydrophobic properties of nitrogen, and hydrogen bond.

9

Three forms of DNA

B,Z,A
B-DNA - predominant form in cells, right handed, 3.4A and 10.4BP
Z-DNA - Formed transiently in cells and left handed, 3.8A, 12BP
A-DNA - Found in DNA-RNA hybrids and is right handed, 2.3A, 11BP

10

Characteristics of DNA

Alkali conditions/heat cause denaturization. Melting point is point where 50% is melted. Details used in PCR/hybridization

11

DNA packaging

DNA is long and must be packaged. Can form high order structures with proteins to package itself. Supercoil structure - coil about itself like a telephone cord

12

Histones

Proteins that function in packaging of DNA. Nucleosome is the organizing unit of chromatin which DNA wraps around, and contains 4 histone molecules (2 of each) - H2A, H2B, H3, H4

13

Chromatin

Form of DNA packaging into a solenoid structures (strings of nucleosomes wound into helical, tubular coils)

14

Histone modifications - Histone transferases

Histone transferases add acetyl group to lysine in the amino terminal tail of histone octamer - weakens bond bond between DNA and histones, opens region in DNA for regulatory proteins to bind, and results in higher level of gene expression.

15

Histone deacetylases

Removes the acetyl group from histones - increases bonding of DNA-histone, results in condensation of DNA and lower levels of gene expression

16

Types of Chromatin -2 types

Heterochromatin - highly condensed (packed), 10% of interphase chromosome, found at center of chromosome (centromere) and ends (telomeres)
Euchromatin - Less condensed, more extended state, 90% of interphase chromosome

17

X-Chromosome Inactivation

Females - One copy of x chomorosome is heterochomatin and becomes inactivated - random and occurs in embryogenesis (results in chimera)

18

RNA - Interaction with DNA and its properties

Can hybridize with DNA; Almost identical property with DNA but single stranded and folds in on itself which contribute to its function

19

mRNA - 3 domains

3 domains - leader sequence - begins with guanosine cap at 5' end
Coding region - includes trinucleotide start codon, trinucleotide codosn for AA, and termination signals
Trailer sequence - Terminates at 3' end with poly(A) tail of up to 200 nucleotides in length

20

Guanosine cap and poly(A) tail

are not encoded by DNA but added after

21

rRNA

Not translated - forms subunits of ribosome with ribosomal protein. Prok. ribosomes smaller than euk. robosomes. Euk. ribosomes contain 4 types of rRNA - 18S, 28S, 5S, and 5.8S. Euk. Cytoplasmic ribosomes are 80S; mitochondrial ribosomes are 55S

22

tRNA

Not translated - 2 functional domains
Anticodon region - recognize a specific 3 nucleotide seq (codon) in mRNA
Amino acid attachment site on opposite side of anticodon region
Cells contain 20 different tRNAs, one for each amino acid

23

What secondary structure does tRNA resemble?

CLoverleaf