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Bio Core Concepts > Function of Nucleotides > Flashcards

Function of Nucleotides Flashcards

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Biology 101 flashcards
1
Q

DNA replication takes place in the ________ during _________

A

Nucleus
Interphase

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2
Q

Describe the process of DNA replication (6 steps)

A
  1. DNA unwinds
  2. Hydrogen bonds holding complementary base pairs break, catalysed by DNA helicase, and the 2 strands separate
  3. Each DNA strand acts as a template
  4. Free DNA nucleotides align opposite their complementary base pairs
  5. DNA polymerase catalyses the condensation reaction between 2 DNA nucleotides. This occurs from the 5 prime to the 3 prime end
  6. Each new DNA molecule is made from one original template strand and one newly replicated strand. This is known as semi-conservative replication
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3
Q

Describe the conservative theory for DNA replication

A

The original double helix molecule remains intact, completely conserved, and a whole new DNA molecule is made

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4
Q

Describe the semi-conservative theory for DNA replication

A

Each strand in the original double helix acts as a template to synthesise a new strand. Each new DNA molecule contains one template strand and one newly replicated strand

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5
Q

Describe the dispersive theory for DNA replication

A

Each new DNA molecule contains fragments of the original double helix and newly replicated DNA

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6
Q

Describe the Meselson-Stahl experiment

A
  1. E.coli was grown in a medium containing amino acids made with the heavy isotope 15N. The bacteria produced nucleotides containing 15N. All the bacteria’s DNA contained this heavy isotope. The DNA was extracted and the suspension then centrifuged
  2. The bacteria were washed and then transferred to a medium containing amino acids with the lighter isotope 14N and allowed to divide once. The DNA was extracted and the suspension then centrifuged
  3. The bacteria were allowed to divide again on the 14N medium. Again the DNA was centrifuged
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7
Q

Explain why the findings of the Meselson-Stahl experiment was conclusive of semi-conservative replication rather than conservative or dispersive

A

After one generation, conservative replication would not give a band in the middle, only a band at the top (light) and at the bottom (heavy). Dispersive would only produce one band, not 2, which would get progressively higher in the tube

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8
Q

Briefly describe transcription

A

It occurs in the nucleus. The genetic code for a specific protein is copied. A complementary strand of mRNA is formed from one template strand of DNA. mRNA leaves the nucleus via the nuclear pore and travels to a ribosome

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9
Q

Briefly describe translation

A

It occurs at a ribosome. The genetic code is translated into a polypeptide. Amino acids that correspond to the codons on the mRNA are brought to the ribosome by tRNA. The amino acids are joined together at the ribosome to form the polypeptide chain.

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10
Q

Describe the process of transcription

A
  • Only one strand of DNA is used as a template strand for the transcription of mRNA
  • The enzyme DNA helicase breaks the hydrogen bonds holding together the base pairs in a specific region of the DNA molecule and the two strands unwind
  • The enzyme RNA polymerase binds to the template strand at the beginning of the sequence to be copied
  • Free RNA nucleotides align opposite complementary base pairs on the template strand
  • RNA polymerase moves along the template strand, catalysing the addition of RNA nucleotides to each other until it reaches a stop codon. Behind the RNA polymerase, the DNA strands rewind
  • mRNA leaves via a nuclear pore and travels into the cytoplasm
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11
Q

What are introns?

A

Non-coding nucleotide sequences in DNA that are removed after transcription by the enzyme endonuclease

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12
Q

What are exons?

A

Exons are the coding sequences which are left behind and spliced together by ligase enzymes to form the final mature mRNA

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13
Q

Does prokaryotic DNA contain introns?

A

No

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14
Q

Suggest how more than one polypeptide could be produced from one gene

A

Introns are removed. Exons can be spliced back together in a different order, thus coding for a different sequence of amino acids, which would result in a different polypeptide

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15
Q

Describe the function of tRNA in translation

A
  • tRNA has a clover leaf shape
  • It’s function is to carry specific amino acids to the ribosome
  • The anti-codon determines which amino acid the tRNA molecule will carry
  • tRNA attaches to the amino acid in the cytoplasm. This process requires ATP and is called ‘amino acid activation’
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16
Q

Describe the function of a ribosome in translation?

A
  • A ribosome is made from protein and rRNA. A ribosome could be free in the cytoplasm or attached to the rough endoplasmic reticulum
  • Each ribosome consistes of a small subunit and a large subunit
  • The large subunit has two attachment sites for tRNA molecules. The smaller subunit binds to the mRNA
17
Q

Describe the initiation stage of translation

A
  1. Ribosome attaches to a start codon on the mRNA
  2. The first tRNA binds to the first attachment site. The anti-codon on the tRNA joins to the complementary codon on the mRNA by hydrogen bonds, forming a codon-anticodon complex
  3. A second tRNA forms a codon-anticodon complex at the second attachment site
18
Q

Describe the elongation stage of translation

A
  1. A ribosomal enzyme catalyses the formation of a peptide bond between the adjacent amino acids
  2. The first tRNA leaves site 1 and returns to the cytoplasm
  3. The ribosome moves down the mRNA one codon so that the second tRNA moves from site 2 to 1
  4. A new tRNA binds to site 2
19
Q

Describe the termination stage of translation

A
  1. Sequence repeats until a stop codon is reached
  2. The ribosome-mRNA-polypeptide complex separates
20
Q

What is a polysome?

A

When many ribosomes move down one mRNA strand. Each ribosome produces a polypeptide so several are made at once

21
Q

Where can the polypeptide be transported to be further modified?

A

Golgi body in vesicles

22
Q

The polypeptide can be folded further or chemically modified by combination with non-proteins such as:

A
  • Carbohydrate to make glycoproteins
  • Lipid to make lipoproteins
  • Phosphate to make phospho-proteins
23
Q

DNA stores genetic information coded in the ________ __ _____

A

Sequence of bases

24
Q

What does the sequence of bases determine?

A

The sequence of amino acids that are joined together to form a polypeptide

25
Q

What is a gene?

A

A section of DNA that codes for a specific polypeptide (one gene - one polypeptide hypothesis)

26
Q

There are __ possible codes, but only __ amino acids found in proteins

A

64 20

27
Q

Why are there more triplet codes than amino acids?

A

Each amino acid has more than one triplet code, the code is then degenerate. Some triplet codons do not code for amino acids but are ‘stop codons’ and mark the end of translation.

28
Q

What is meant by ‘the genetic code is universal?

A

The same triplet codes for the same amino acid in all living organisms

29
Q

What is meant by ‘the genetic code is non-overlapping?

A

Each base in the sequence occurs in only one triplet

Bio Core Concepts (6 decks)

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