Chapter 8 and 9: DNA and genomics

Structure of a nucleotide

Deoxyribonucleotides have -OH Group at C2. T/F?

F. Ribonucleotides have -OH group at C2. Deoxyribonucleotides only have H.

What are the purines?

Adenine and guanine

What are the pyrimidines?

Cytosine and thymine

What is the bond that links adjacent nucleotides?

Phosphodiester bond

Draw a short segment of RNA and label the phosphodiester bond

What ratios are 1:1?

Purine: pyrimidines; A:T; C:G

Explain the importance of the ratios A to T and G to C in DNA

• Ratios of A to T and G to C is approximately 1:1 in DNA

• Indicating CBP whereby A base pairs with T and C base pairs with G

• H bonds formed between complementary base pairs help to stabilize structure

• Pairing between a purine and a pyrimidines will ensure DNA molc has a constant width of 2.0nm

RNA is ___ stranded but can ___ back upon itself and have ___ stranded regions

Single; fold; double

What is semi-conservative replication?

• Both DNA strand separate by breaking of hydrogen bonds

• Each strand acts as a template for synthesis of new strand through CBP

• New DNA molecule consists of 1 original strand and 1 newly synthesised strand

Explain the Uv absorption peaks observed in gen 1 and gen 2

• During semiconservative replication, original 15N-15N DNA strands unzipped and served as templates for formation of new strands

• Since only 14N DNA present in medium resulting DNA molecules in gen 1 were hybrid DNA molecules, consisting of 1 original 15N strand and 1 newly synthesised 14N strand

• Each hybrid DNA molecule from gen 1 unzipped and used as templates for DNA replication

• 50% of DNA in gen 2 were made up of hybrid 14N-15N DNA → middle peak; the other 50% were made up of light 14N-14N DNA → leftmost peak

Why is DNA a suitable store of information?

• Can be replicated accurately so that daughter cells have identical copies of DNA as parent cell

• Stable molecule → can be passed on to next generation without loss of coded info

• Backup of code

• Coded information can be easily accessed

What enzymes are involved in DNA synthesis?

Helicase, topoisomerase, primase, DNA polymerase, another DNA polymerase, DNA ligase

Types of DNA mutations

Single base substitution, inversion, insertion, deletion

Effects of DNA mutations

Frameshift mutation, missense mutation, silent mutation, nonsense mutation

Which globin is affects in sickle-cell disease?

B

Describe the changes in DNA, mRNA and AA in sickle cell disease

CTC to CAC, GAG to GUG, Glutamate to valine

Explain the significance of change in AA to the properties of Hb

• Charged, hydrophilic glutamate is replaced by non-polar, hydrophobic valine

• Changes in the primary, secondary, tertiary structure as change in the R groups and bonds formed affect the way the polypeptide folds

• At low O2 concentrations, loss of O2 from HbS results in conformational change and hydrophobic patches on HbS stick out

• Hydrophobic areas of different HbS molecules stick together and HbS polymerizes, forming absorbable, long, rigid, rod-like fibres that distorts the shape of biconcave RBC and make it sickle shaped

Effect of change in AA in Hb

• Long insoluble HbS fibres within RBC → normal biconcave shape distorted into sickle shape

• Sickle RBC more fragile → shorter lifespan → shortage of RBC and poor O2 transport → anaemia

• Sickle RBC are pointed and elongated → may get lodged in small blood vessels → interfere with blood circulation → organ damage

Characteristics of genetic code

• Every code is a triplet code

• Code is universal

• Code is degenerate

• Code is non-overlapping

• Code is continuous

• Includes ‘stop’ and ‘start’ sequences

Name the start codon and the corresponding amino acid

AUG, methionine

Name the stop codons

UAG, UAA, UGA

Aneuploidy

Condition where the cell does not have a chromosome number that is a multiple of the haploid number. There are extra or fewer chromosomes present compared to the wild type.

Non-disjunction

When homologous chromosomes/ sister chromatids fail to separate properly to opposite poles. Can occur during meiosis or mitosis/