Week 5 Flashcards
What does DNA stand for
Deoxyribonucleic acid
What is DNA
=at the heart of genes and genetics
- a polymer
- each subunit of polymer is a nucleotide
What are the 3 things nucleotides are comprised of
- phosphate group
- a 5 Carbon sugar ( 2-Deoxyribose)
- 1 of 4 cyclic nitrogenous bases
What are the 2 groups of nitrogenous bases?
+ what nitrogenous bases are in each group
2 groups: purine and pyrimidine
Purine: Adenine (A) & Guanine (G)
Pyrimidine: Thymine (T) and Cytosine (C)
How are purine and pyrimidine nucleotide chains connected?
By phosphodiester bonds
What are phoshodiester bonds
= the sugar-phosphate backbone of DNA
True / False : DNA strands are polar
True
What is the difference between the 5’end and the 3’end?
5’ end has a free phosphate group
3’ end has a free hydroxyl group
True or False: DNA is double-stranded and run parallel
False. DNA is double-stranded, but runs anti-parallel
DNA is a double helix that is left/right handed?
right-handed, meaning it runs clockwise
FIll in the blank:
Strands are held together by _____ bonds between bases on opposite strands.
Strands are held together by _______ interactions between _________ stacked bases
Strands are held together by “hydrogen” bonds between bases on opposite strands.
Strands are held together by “hydrophobic” interactions between “adjacent” stacked bases
Fill in the blank:
Opposing strands are said to be ________.
Opposing strands are said to be “complimentary”
How are bases paired and how are they mediated?
A = T and G = C
They are mediated by Hydrogen bonds
Define b Dna.
= the most common form of DNA
WHat are the 2 grooves of different width?
- Major grooves
2. Minor grooves
The right-handed helix is. ______ per turn
a) 5 base pairs
b) 10 base pairs
c) 20 base pairs
b) 10 bp
What are eukaryotic chromosomes composed of
- DNA
- RNA
- proteins
Define and describe the 1st level of condensation?
-What metaphor is associated with this?
=packing DNA into nucleosomes
- produces a 10nm fibre
- DNA wraps around the nucleosome cores of 8 histone proteins (+ ancored by a 9th)
- The space inbetween the nucleosomes is connected by Linker DNA
- 146 bp of DNA wrapped 1 3/4 turns around histone
“beads-on-a-string” view of chromatin
What are nucleosomes made up of?
made up of 8 histone proteins
Name the histone proteins that have 2 molecules each
H2A, H2B, H3, H4 are in the nucleosomal core
+ 1 molecules of Histone H1 to further stabilize the structure
What is H1 and what does it do
=the linker histone
-it further stabilizes the structure
Define and describe the 2nd level of condensation.
= an additional folding / supercoiling of 11nm fibre to produce a 30nm fibre
-driven by nucleosomal interactions
-H1 = involved
2 models that describe the structure : solenoid and the zig-zag models
What are the 2 models that describe the structure that occures in the 2nd level of condensation?
- solenoid
2. zig-zag models
Define the 3rd level of condensation
= attachment of the 30nm fibre at many positions to a (non-histone) protein scaffold
WHat is the 30nm fibre?
= the basic structural unit of the metaphase chromosome
-DNA in its most condensed form
GIve a summary of the levels of condensation.
Level 1 : packing DNA into nucleosomes
Level 2 : an additional folding / supercoiling of 11nm fibre to produce a 30nm fibre
Level 3 : attachment of the 30nm fibre at many positions to a (non-histone) protein scaffold
Where else can you also find DNA that exist in circular chromosomes, besdies the nucleus?
Mitochondria and Chloroplasts
What is the 4 function of telomeres.
- they protect the ends of the chromosomes
the “aglet” - resist degration by DNases (attacking enzymes)
- prevent fusion of chromosomal ends
- facilitate replication of the ends of the inear DNA
- encode not important information
What is the function of the centromere
provide the point of attachment of sister chromatids and of the chromosomes to microtubles in the mitotic spinde
What is the 2 step process of the transfer of information from DNA to protein in all organisms
- Transcription
2. Translation
What happens during Transcription
= information is transferredfrom DNA to an RNA molecule
What happens during Translation
Information is transferred from RNA to a protein through a code that specifies the amino acid sequence
Define the central dogma of molecular biology
DNA –> RNA –> Protein
What is the difference between RNA and DNA
- RNA uses a ribose sugar ( has another OH)
- has the pyrimidine uracil (T) instead of thymine
- A=U instead of A=T - RNA is single stranded
RNA is less stable than DNA. Explain why
the 2’ hydroxyl group makes RNA more reactive than DNA, therefore RNA is less stable
RNA is synthesized in a _’ to a _’ direction. Is this the same as or different to DNA polymerase.
What is the template strand direction that the RNA uses to transcribe
5’ to 3’ direaction. This is the same as DNA polymerase
The template strand the RNA reads off of is 3’ to 5’
True or false: The initionation of RNA synthesis requires a primer
False. It does not need a primer
Are new nucleotides added to the 5’ or 3’ end of the RNA molecule?
the 3’ end
The DNA double helix is locally unwound during transcription or translation?
Transcription
Define promoter
the region of DNA that is upstream of transcribed region
