1 Nucleic Acids And Chromosomes Flashcards
Q: What joins monomers of nucleic acids? How? What are monomers called?
A: monomer= nucleotides
PHOSPHODIESTER LINK
The 3’-OH of sugar of one nucleotide is linked to phosphate group, which in turn is joined to 5’-OH of adjacent sugar on the adjacent nucleotide
Q: What is the 3D structure of DNA? (3)
A: double helix- 2 chains wrapped around each other -> bases within and 2 sugar phosphate backbones surrounding for support
antiparallel
where each chain has 2 ends- The first nucleotide in a sequence has a free 5’ phosphate and the last nucleotide in the sequence has a free 3’ hydroxyl group (Conventionally, DNA sequences are written from the 5’ end to the 3’ end)
Q: What are the components of a nucleoside? nucleotide?
A: sugar and base
sugar and base and phosphate
Q: What’s the difference between deoxyribose and ribose? What are they both?
A: deoxy lacks an oxygen that ribose has
both are sugars
Q: Which number carbon of the sugar is attached to the base? By which bond?
A: 1 by glycosidic bond
Q: What are the 5 bases?
A: guanine, adenine, uracil, thymine, cytosine
Q: Which bases are purine? What makes them a purine?
A: guanine, adenine
double ring structure (larger)
Q: Which bases are pyrimidine? What makes them a pyrimidine?
A: uracil, thymine, cytosine
single ring structure (smaller)
Q: How would you recognise adenine?
A: double ring structure, amino group
Q: How would you recognise guanine?
A: double ring structure, amino group and carbonyl group
Q: How would you recognise cytosine?
A: single ring structure, amino group, carbonyl group
Q: How would you recognise thymine?
A: single ring structure, 2 carbonyl group and methyl group
Q: How would you recognise uracil?
A: single ring structure, 2 carbonyl group
Q: In Watson crick base pairing which bases join and by how many hydrogen bonds? Which is more stable?
A: C to G by 3 more stable
A to T/U by 2
Q: What part of the DNA structure carries genetic info?
A: bases
Q: What is the method for separating the 2 strands of DNA? When/where does this occur?
A: melt/low salt -> melts/denatures
cells when replicating/ induced in labs
Q: What is the method for annealing the 2 complementary strands of DNA?
A: cooling/high salt -> re anneal/ hybridise
Q: What is a karyotype? Why are karyotypes an important diagnostic tool?
A: Organised profile of someone’s chromosomes
in some diseases a chromosomes may be comprised of several different chromosomes
Q: What does a diploid human cell contain in terms of genetic information? Difference between male and female?
A: 22 pairs of autosomal chromosomes (homologous) and a pair of sex chromosomes
XX for female
XY for male
Q: Where do the major and minor grooves occur in DNA?
A: The major groove occurs where the backbones are far apart, the minor groove occurs where they are close together
Q: Compare the genomes of E.coli and Homo Sapiens.
A: E.coli has 4.6 x 10^6 base pairs in a single circular double stranded molecule with a length of 1.4mm
around 3 x 10^9 base pairs of DNA divided in chromosomes that each contain a single linear double helical DNA molecule of around 200 x 10^6 base pairs
Q: What is a genome?
A: the entire DNA coding for an organism
Q: When are chromosomes visible? not?
A: just before cells divide but not in non dividing cells
Q: Describe mitotic chromosomes. DNA appearance?
A: highly condensed form of chromosomes
DNA is visible
Q: Describe interphase chromosomes. DNA appearance?
A: extended form of chromosomes (non dividing= loose)
less compact that mitotic form of chromosomes
DNA is not visible
Q: Describe the packaging of eukaryotic DNA. Include nucleosomes.
A: DNA is tightly packed forming a complex with proteins - the complex is called CHROMATIN
NUCLEOSOMES - lowest level of packing - consists of DNA wrapped around 8 histones with linker DNA between histones
1 histone between the nucleosomes
Q: Are histones positively or negatively charged? What does this result in?
A: Histones are positively charged so interact closely with the negatively charged sugar phosphate backbone
Q: Around how many base pairs of DNA are there per nucleosome?
A: 200
Q: What fold condensing of DNA do nucleosomes cause?
A: 7
Q: How is the chain of nucleosomes further packed? What fold condensing of DNA does this cause
A: FIBER - the nucleosomes are further packed to generate a more compact structure with around 40 fold condensing of DNA.
Q: What does chromatin contain?
A: DNA and proteins
