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Biology > 2.1.3 - NUCLEOTIDES + NUCLEIC ACIDS > Flashcards

2.1.3 - NUCLEOTIDES + NUCLEIC ACIDS Flashcards

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1
Q

What are the molecules in a nucleotide?

A
  • Carbon
  • Hydrogen
  • Oxygen
  • Nitrogen
  • Phosphorus
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2
Q

What are the three main components of nucleotides?

A
  • A pentose sugar (5 carbon atoms)
  • A nitrogenous base
  • A phosphate group
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3
Q

What is a nucleotide?

A

The monomer that makes up DNA and RNA (types of nucleic acid)

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4
Q

What are the three main components of DNA nucleotides?

A
  • A deoxyribose sugar with hydrogen at the 2’ position (carbon)
  • A phosphate group
  • One of four nitrogenous bases - adenine (A), cytosine(C), guanine(G) or thymine(T)
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5
Q

What are the three main components of RNA nucleotides?

A
  • A ribose sugar with a hydroxyl (OH) group at the 2’ position (carbon)
  • A phosphate group
  • One of four nitrogenous bases - adenine (A), cytosine(C), guanine(G) or uracil (U)
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6
Q

How do nucleotides join together?

A

Phosphodiester bonds

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7
Q

What type of base are adenine and guanine?

A

Purine

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8
Q

What type of base are cytosine and thymine?

A

Pyrimidine

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9
Q

Describe the structure of a purine base.

A

Contains two carbon-nitrogen rings joined together

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10
Q

Describe the structure of a pyrimidine base.

A

Only has one carbon-nitrogen ring
(smaller than a purine base)

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11
Q

Describe the structure of DNA.

A
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12
Q

Describe the structure of RNA.

A
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13
Q

State the components of ATP.

A

Adenosine Triphosphate contains adenine, a ribose sugar and three phosphate groups

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14
Q

State the components of ADP.

A

Adenosine Diphosphate contains adenine, a ribose sugar and two phosphate groups

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15
Q

Define phosphorylate

A

introduce a phosphate group into (a molecule or compound)

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16
Q

What does ATP do?

A
  • Provides energy for chemical reactions in the cell
  • Synthesised from ADP and inorganic phosphate using the energy from an energy-releasing reaction (e.g. breakdown of glucose in respiration
  • ADP is phosphorylated to form ATP and a phosphate bond is formed
  • Energy is formed in the phosphate bond
  • When energy is needed by a cell, ATP is broken back down into ADP and inorganic phosphate - energy is released from the phosphate bond and used by the cell
17
Q

How are polynucleotides formed?

A
  • Nucleotides join up between the phosphate group of one nucleotide and the sugar of another via a condensation reaction - forms a phosphodiester bond (consisting of the phosphate group + 2 ester bonds
  • The chain of sugars and phosphates is known as the sugar-phosphate backbone
  • Polynucleotides can be broken down into nucleotides again by breaking the phosphodiester bonds (hydrolysis reaction)
18
Q

How is a double helix formed?

A
  • Two DNA polynucleotides strands join together by hydrogen bonding between the bases
  • Each base can only join with one particular partner (complementary base pairing)
  • Adenine always pairs with Thymine (A-T) and Cytosine always pairs with Guanine (C-G) - A prune always pairs with a pyrimidine
  • 2 H bonds form between A and T, and 3 H bonds form between C and G
  • Two antiparallel (running in opposite directions) polynucleotide strands twist to form the DNA double helix
19
Q

How does DNA copy itself before cell division?

A
  • DNA helicase (enzyme) breaks the hydrogen bonds between the two polynucleotide DNA strands - the helix unzips to form two single strands
  • Each original single strand acts as a template for a new strand - free-floating DNA nucleotides join to the exposed bases on each original template strand by complementary base paring (A with T and C with G)
  • The nucleotides of the new strand are joined together by the enzyme DNA polymerase - forms the sugar-phosphate backbone | H bonds form between the bases on the original and new strand - strands twist to form a double helix
  • Each new DNA molecule contains one strand from the original DNA molecule and one new strand

This is called SEMI-CONSERVATIVE REPLICATION because half of the strand in each new DNA molecule are from the original DNA piece
DNA replication is really accurate

20
Q

What may randomly occur during DNA replication?

A
  • A random, spontaneous mutation may occur
  • A mutation is any change to the DNA base sequence
  • Don’t always have an effect, but can also the sequence of amino acids in a protein
    ^— may cause abnormal protein to be produced which may function better or not work at all
21
Q

What is a gene?

A

A sequence of DNA nucleotides that codes for a polypeptide
Amino acid sequence in a polypeptide forms the primary structure

22
Q

How are amino acids coded in DNA?

A
  • Each amino acid is coded for by a sequence of three bases (called a triplet) in a gene
  • Difference base sequences code for different amino acids - so the sequence of bases in a section of DNA is a template that is used to make proteins during protein synthesis
23
Q

What happens to DNA in protein synthesis?

A
  • DNA molecules are found in the nucleus of the cells, but the organelles that make proteins are found in the cytoplasm
  • DNA is too large to move out of the nucleus, so a section is copied into mRNA - this is transcription
  • mRNA leaves the nucleus and joins with a ribosome in the cytoplasm, where it can be used to synthesise a protein - this is translation
24
Q

What are the three types of RNA

A
  • Messenger RNA (mRNA)
  • Transfer RNA (tRNA)
  • Ribosomal RNA (rRNA)
25
Q

What is the function of mRNA?

A
  • made in the nucleus
  • three adjacent bases are called a codon
  • carried the genetic code from the DNA in the nucleus to the cytoplasm, where its used to make a proteins during translation
26
Q

What is the function of tRNA?

A
  • found in the cytoplasm
  • has an amino acid binding site at one end + a sequence of three bases at the other end called an anticodon
  • carried the amino acids that are used to make proteins to the ribosome during translation
27
Q

What is the function of rRNA?

A
  • forms the two subunits in a ribosome
  • the ribosome moves alone the mRNA strand during protein synthesis - the mRNA in the ribosome helps to catalyse the formation of peptide bonds between the amino acids
28
Q

What is the genetic code?

A

The sequence of base triplets (codons) in DNA or mRNA, which codes for specific amino acids

29
Q

Why is the genetic code described as non-overlapping?

A

In the genetic code, each base triplet is read in sequence, separate from the triplet before it and after it

Base triplets don’t share their bases

30
Q

Why is the genetic code describe as degenerate?

A
  • There are more possible combinations of triplets than there are amino acids (20 amino acids but 64 possible triplets)
  • Means that some amino acids are coded for by more than one base triplet (e.g. tyrosine can be coded for by UAU or UAC)
31
Q

Why is the genetic code describe as universal?

A

The same specific base triplets code for the same amino acids in all living things (e.g. UAU codes for tyrosine in all organisms)

32
Q

What are the two stages of protein synthesis called?

A

Transcription and Translation

33
Q

Describe what happens in transcription

A
  • Begins when RNA polymerase attaches to the DNA double helix at the beginning of a gene
  • The Hydrogen bonds between the two DNA strands in the gene break, separating the strands - the DNA molecule uncoils at that point
  • One of the strands is then used as a template to make and mRNA copy
  • The RNA polymerase lines up free RNA nucleotides alongside the template strand - complementary base pairing means that the mRNA strand ends up being a complementary copy of the DNA template trans (except T is replaced by U in RNA)
  • One the RNA nucleotides have paired up with their specific bases on the DNA strand they’re joined together, forming and mRNA molecule
  • The RNA polymerase moves along the DNA, separating the strands assembling the mRNA strand
  • The h bonds between the uncoiled strands of DNA re-form once the RNA polymerase has passed by and the strands coil back into a double helix
  • When RNA polymerase reaches a stop codon, it stops making mRNA and detached from the DNA
  • The mRNA moves out of the nucleus through a nuclear pore and attaches to a ribosome in the cytoplasm, where the next stage of protein synthesis takes place
34
Q

Describe what happens in translation

A
  • The mRNA attaches itself to a ribosome and tRNA molecule carry amino acids to the ribosome
  • A tRNA molecule, with an anticodon that’s complementary to the start codon on the mRNA, attaches itself to the mRNA by complementary base pairing
  • A second tRNA molecule attaches itself to the next codon on the mRNA in the same way
  • rRNA in the ribosome catalyses the formation of a peptide bond between the two amino acids attached to the tRNA molecules - this joins the amino acids together | The first tRNA molecule moves away, leaving its amino acid behind
  • A third tRNA molecule binds to the next codon on the mRNA - its amino acid binds to the first two and the second tRNA molecule moves away
  • This continues, producing a chain of linked amino acids (a polypeptide chain) until there;s a stop codon on the mRNA molecule
  • The polypeptide chain moves away from the ribosome and translation is complete

Biology (26 decks)

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