What is a nucleotide?
A molecule consisting of 5 carbon sugar and, a phosphate group and a nitrogenous base which form monomers of DNA and RNA
What is the difference between RNA and DNA?
RNA has ribose sugar and DNA has deoxyribose sugar.
What is a polynucleotide?
Large molecule containing lots of nucleotides.
What are the 4 nitrogenous bases?
Adenine, Cytosine, Guanine and Thymine
Explain the conservative replication theory.
A completely new double stranded copy of DNA is made so one daughter DNA molecule is new and has one parent strand.
Is the conservative replication theory correct?
No.
What is the semi conservative theory?
The DNA strands separate and each strand acts as a template so that both daughter DNA molecules have one new strand and one parent strand.
Which nitrogenous bases pair together?
Adenine and Thymine
Cytosine and Guanine
How many hydrogen bonds are between adenine and thymine?
2
How many hydrogen bonds are between cytosine and guanine?
3
Which of the nitrogenous bases are purines?
Adenine and Guanine.
Which of the nitrogenous bases are pyrimidines?
Cytosine and Thymine.
What is the difference between a pyrimidine and a purine?
Purine has 2 rings and pyrimidine has 1.
Describe the structure of DNA.
Antiparallel strands
Phosphodiester bond between sugar and phosphate group
What do hydrogen bonds allow?
The DNA to unzip
Describe DNA in eukaryotic cells.
In nucleus
A loop of DNA in mitochondria
Describe DNA in prokaryotic cells.
DNA is in a loop add in cytoplasm.
What is DNA polymerase?
Joins new nucleotides on each of the new strands.
What is DNA helicase?
Breaks hydrogen bonds to split the strands apart.
What is DNA ligase?
Adds phosphate groups into any gaps on the sugar phosphate backbone on the DNA molecule.
What are the steps of DNA replication?
- DNA helicase breaks down hydrogen bonds which unzips the strands.
- Free nucleotides are attracted to their complementary base pairs.
- Each chain acts as a template.
- Once in place the nucleotides are joined together by DNA polymerase making strong covalent bonds forming a backbone.
What direction does DNA polymerase work in?
Only one.
Describe ATP.
High energy bonds between phosphate groups.
Made in respiration and used as an energy currency within cell.
Describe RNA.
3 forms: mRNA, tRNA and rRNA
What does tRNA do?
Transfer, brings amino acids to ribosome.
What does mRNA do?
Messenger, takes genetic code from the nucleus to ribosome.
What does rRNA do?
Ribosomes are made of rRNA.
What is Meselson and Stahl’s evidence?
E. Coli grown on medium containing the heavy isotope of Nitrogen N15 for many generations, so all DNA contained heavy N.
The bacteria was transferred to a medium containing the lighter isotope n14 for 1 or 2 or 3 generations.
After 1,2,3 generations, the cells were killed, the DNA extracted and centrifuged.
15N DNA will sink further than 14N.
The samples are visualized under UV light.
What does universal mean?
That every known organism has DNA.
What does non overlapping mean?
Same letter is not used in more than one different codon.
What does degenerate mean?
Each amino acid can be coded for by more than one amino acid.
How many possible codes are there?
64
What is transcription?
A gene unzips and hydrogen bonds between bases break.
mRNA passes out through nuclear envelope and attaches to ribosome.
What is translation?
tRNA from the nucleus pass out into the cytoplasm.
tRNA brings amino acids to find their place.
A ribosome moves along mRNA which reads the code .
mRNA breaks down.
What does every protein start with?
Methionine.
Uracil replaces what?
Thymine.
What bases don’t code (stop)?
UAA
UAG
UGA
