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alevel biology OCR > Nucleic Acids > Flashcards

Nucleic Acids Flashcards

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1
Q

What is a nucleotide?

A

A molecule consisting of 5 carbon sugar and, a phosphate group and a nitrogenous base which form monomers of DNA and RNA

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2
Q

What is the difference between RNA and DNA?

A

RNA has ribose sugar and DNA has deoxyribose sugar.

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3
Q

What is a polynucleotide?

A

Large molecule containing lots of nucleotides.

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4
Q

What are the 4 nitrogenous bases?

A

Adenine, Cytosine, Guanine and Thymine

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5
Q

Explain the conservative replication theory.

A

A completely new double stranded copy of DNA is made so one daughter DNA molecule is new and has one parent strand.

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6
Q

Is the conservative replication theory correct?

A

No.

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7
Q

What is the semi conservative theory?

A

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.

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8
Q

Which nitrogenous bases pair together?

A

Adenine and Thymine

Cytosine and Guanine

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9
Q

How many hydrogen bonds are between adenine and thymine?

A

2

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10
Q

How many hydrogen bonds are between cytosine and guanine?

A

3

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11
Q

Which of the nitrogenous bases are purines?

A

Adenine and Guanine.

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12
Q

Which of the nitrogenous bases are pyrimidines?

A

Cytosine and Thymine.

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13
Q

What is the difference between a pyrimidine and a purine?

A

Purine has 2 rings and pyrimidine has 1.

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14
Q

Describe the structure of DNA.

A

Antiparallel strands

Phosphodiester bond between sugar and phosphate group

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15
Q

What do hydrogen bonds allow?

A

The DNA to unzip

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16
Q

Describe DNA in eukaryotic cells.

A

In nucleus

A loop of DNA in mitochondria

17
Q

Describe DNA in prokaryotic cells.

A

DNA is in a loop add in cytoplasm.

18
Q

What is DNA polymerase?

A

Joins new nucleotides on each of the new strands.

19
Q

What is DNA helicase?

A

Breaks hydrogen bonds to split the strands apart.

20
Q

What is DNA ligase?

A

Adds phosphate groups into any gaps on the sugar phosphate backbone on the DNA molecule.

21
Q

What are the steps of DNA replication?

A
  1. DNA helicase breaks down hydrogen bonds which unzips the strands.
  2. Free nucleotides are attracted to their complementary base pairs.
  3. Each chain acts as a template.
  4. Once in place the nucleotides are joined together by DNA polymerase making strong covalent bonds forming a backbone.
22
Q

What direction does DNA polymerase work in?

A

Only one.

23
Q

Describe ATP.

A

High energy bonds between phosphate groups.

Made in respiration and used as an energy currency within cell.

24
Q

Describe RNA.

A

3 forms: mRNA, tRNA and rRNA

25
Q

What does tRNA do?

A

Transfer, brings amino acids to ribosome.

26
Q

What does mRNA do?

A

Messenger, takes genetic code from the nucleus to ribosome.

27
Q

What does rRNA do?

A

Ribosomes are made of rRNA.

28
Q

What is Meselson and Stahl’s evidence?

A

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.

29
Q

What does universal mean?

A

That every known organism has DNA.

30
Q

What does non overlapping mean?

A

Same letter is not used in more than one different codon.

31
Q

What does degenerate mean?

A

Each amino acid can be coded for by more than one amino acid.

32
Q

How many possible codes are there?

A

64

33
Q

What is transcription?

A

A gene unzips and hydrogen bonds between bases break.

mRNA passes out through nuclear envelope and attaches to ribosome.

34
Q

What is translation?

A

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.

35
Q

What does every protein start with?

A

Methionine.

36
Q

Uracil replaces what?

A

Thymine.

37
Q

What bases don’t code (stop)?

A

UAA
UAG
UGA

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