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Biology > Nucleotides > Flashcards

Nucleotides Flashcards

1
Q

What are nucleotides used to make?

A

Nucleic acids

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2
Q

What are nucleotides made from?

A

A is a type of biological molecule. It’s made from:
Nucleotide
• a pentose sugar (that’s a sugar with 5 carbon atoms),
• a nitrogenous (nitrogen-containing) base,
• a phosphate group.

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3
Q

What do all nucleotide contain?

A

All nucleotides contain the elements C, H, O, N and P.

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4
Q

Why are nucleotides important?

A

2) Nucleotides are really important. For a start, they’re the monomers (see p. 22) that make up DNA and RNA.
DNA and RNA are both types of nucleic acid. DNA is used to store genetic information — the instructions
an organism needs to grow and develop. RNA is used to make proteins from the instructions in DNA.
3) ADP and ATP are special types of nucleotide (see next page).
They’re used to store and transport energy in cells.

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5
Q

Whats the sugar in DNA called?

A

Deoxyribose

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6
Q

What does each DNA have the same?

A

Each DNA nucleotide has the same sugar and a phosphate group.
The base on each nucleotide can vary though.

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7
Q

How many bases are there?

A

4

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8
Q

What are the 4 possible bases?

A

There are four possible bases — adenine (A), thymine (T),

cytosine (C) and guanine (G).

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9
Q

What are 2 purines?

A

Adenine and guanine are a type of base called a purine.

Cytosine and thymine are a type of base called a pyrimidine.

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10
Q

What are 2 pyrimidine?

A

Cytosine and thymine are a type of base called a pyrimidine

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11
Q

Whats a purine?

A

A purine base contains two carbon-nitrogen rings joined together.

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12
Q

Whats a pyrimidine?

A

A pyrimidine base only has one carbon-nitrogen ring.

So a pyrimidine base is smaller than a purine base.

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13
Q

A molecule of DNA contains how many polynucleotide chains?

A

A molecule of DNA contains two polynucleotide chains — each chain
is made up of lots of nucleotides joined together.

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14
Q

What is sugar in RNA called?

A

The Sugar in RNA is Called Ribose

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15
Q

RNA

A

RNA (ribonucleic acid) contains nucleotides with a ribose sugar
(not deoxyribose).
2) Like DNA, an RNA nucleotide also has a phosphate group and one of four different bases.
3) In RNA though, uracil (a pyrimidine) replaces thymine as a base.
4)An RNA molecule is made up of a single polynucleotide chain.

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16
Q

What are ADP and ATP?

A

ADP and ATP are Phosphorylated Nucleotides

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17
Q

To phosphorylate a nucleotide you need?

A

1) To phosphorylate a nucleotide, you add one or more phosphate groups to it.
2) ADP (adenosine diphosphate) contains the base adenine, the sugar ribose and two phosphate groups.
3) ATP (adenosine triphosphate) contains the base adenine, the sugar ribose and three phosphate groups.

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18
Q

What is ATP?

A

• ATP provides energy for chemical reactions in the cell.
• ATP is synthesised from ADP and inorganic phosphate (P ) using the energy from
i
an energy-releasing reaction, e.g. the breakdown of glucose in respiration.
The ADP is phosphorylated to form ATP and a phosphate bond is formed.
• Energy is stored in the phosphate bond. When this energy is needed by a cell, ATP is broken back down
into ADP and inorganic phosphate (P (. Energy is released from the phosphate bond and used by the cell.

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19
Q

Nucleotides Join Together to Form?

A

Nucleotides Join Together to Form Polynucleotides

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20
Q

How do Nucleotides Join Together to Form Polynucleotides?

A

1) The nucleotides join up between the phosphate group of one
nucleotide and the sugar of another via a condensation reaction.
This forms a phosphodiester bond (consisting of the phosphate group and two ester bonds).
2) The chain of sugars and phosphates is known
as the sugar-phosphate backbone.
3) Polynucleotides can be broken down into nucleotides again by
breaking the phosphodiester bonds (using hydrolysis reactions).

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21
Q

Two Polynucleotide Strands Join Together to Form?

A

Two Polynucleotide Strands Join Together to Form a Double-Helix

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22
Q

How do Two Polynucleotide Strands Join Together to Form a Double-Helix?

A

1) Two DNA polynucleotide strands join together by hydrogen bonding between the bases.
2) Each base can only join with one particular partner — this is called complementary base pairing.
3) Adenine always pairs with thymine (A - T) and cytosine always pairs with guanine (C - G).
A purine (A or G) always pairs with a pyrimidine (T or C).
4) Two hydrogen bonds form between A and T, and three hydrogen bonds form between C and G.
5) Two antiparallel (running in opposite directions) polynucleotide strands twist to form the DNA double-helix.

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23
Q

How to Purify DNA Using a Precipitation Reaction?

A

1) Break up the cells in your sample (probably a bit of onion or something). You can do this using a blender.
2) Make up a solution of detergent (a dilute washing-up liquid will do), salt (sodium chloride) and distilled water.
3) Add the broken-up cells to a beaker containing the detergent solution.
Incubate the beaker in a water bath at 60 °C for 15 minutes.
The detergent in the mixture breaks down the cell membranes. The salt binds to the DNA and causes it to clump together.
The temperature of the water bath should stop enzymes in the cells from working properly and breaking down the DNA.4) Once incubated, put your beaker in an ice bath to cool the mixture down. When it’s
cooled, filter the mixture. Transfer a sample of your mixture to a clean boiling tube.
5) Add protease enzymes to the filtered mixture.These will break down some proteins in the mixture, e.g. proteins bound to the DNA. Adding RNase enzymes will break down any RNA in the mixture.
6) Slowly dribble some cold ethanol down the side of the tube,
so that it forms a layer on top of the DNA-detergent mixture.
7) If you leave the tube for a few minutes, the DNA will form a white precipitate
(solid), which you can remove from the tube using a glass rod.

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24
Q

What does DNA do before cell division?

A

DNA copies itself before cell division so that each new cell has the full amount of DNA.

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25
Q

Step 1 of self replication?

A

1) DNA helicase (an enzyme) breaks the hydrogen
bonds between the two polynucleotide DNA strands.
The helix unzips to form two single strands.

26
Q

Step 2 of self replication?

A 
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 pairing
— A with T and C with G.
27
Q

Step 3 of self replication?

A

3) The nucleotides of the new strand are joined together by the enzyme DNA polymerase. This forms the sugar-phosphate backbone.
Hydrogen bonds form between the bases on the original and new
strand. The strands twist to form a double-helix.

28
Q

Step 4 of self replication?

A

Each new DNA molecule contains
one strand from the original DNA
molecule and one new strand.

29
Q

Whats this type of copying called?

A

is type of copying is called semi-conservative replication because half of the strands in each new DNA
molecule are from the original piece of DNA (i.e. the new molecule contains one old strand and one new strand).
2) DNA replication is really accurate — it has to be, to make sure genetic information
is conserved (stays the same) each time the DNA in a cell is replicated.
3) Every so often though, a random, spontaneous mutation occurs. A mutation is any change to the DNA
base sequence. Mutations don’t always have an effect, but they can alter the sequence of amino acids
in a protein (see next page). This can cause an abnormal protein to be produced. The abnormal protein
might function better than the normal protein — or it might not work at all.

30
Q

What does DNA contain?

A

Genes which are instructions for making proteins

31
Q

What are genes?

A

1) A gene is a sequence of DNA nucleotides that codes for a polypeptide — the sequence of
amino acids in a polypeptide forms the primary structure of a protein

32
Q

Different proteins have a different number and order of?

A

amino acids

33
Q

What determines the order of amino acids in a particular protein?

A

3) It’s the order of nucleotide bases in a gene that determines the order of amino acids in a particular protein.

34
Q

Each amino acid is coded for by a?

A

Each amino acid is coded for by a sequence

of three bases (called a triplet) in a gene.

35
Q

Different sequences of bases code for different?

Different sequences of bases code for?

A

Different sequences of bases code for different amino acids. So the sequence of bases in
a section of DNA is a template that’s used to make proteins during protein synthesis.

36
Q

DNA is Copied into RNA for?

A

DNA is Copied into RNA for Protein Synthesis

37
Q

How is DNA is Copied into RNA for Protein Synthesis?

A

1) DNA molecules are found in the nucleus
of the cell, but the organelles that make
proteins (ribosomes, see page 11)
are found in the cytoplasm.
2) DNA is too large to move out of the
nucleus, so a section is copied into
mRNA (see below). This process is
called transcription (see page 40).
3) The mRNA leaves the nucleus and joins with
a ribosome in the cytoplasm, where it can
be used to synthesise a protein. This process
is called translation (see page 41).

38
Q

How many main types of RNA are there?

A

There are Three Main Types of RNA

39
Q

What are the 3 main types of RNA?

A

mRNA
tRNA
rRNA

40
Q

What is Messenger RNA (mRNA)?

A

Messenger RNA (mRNA)
• Made in the nucleus.
• Three adjacent bases are called a codon.
• It carries the genetic code from the DNA
in the nucleus to the cytoplasm, where it’s
used to make a protein during translation.

41
Q

What is Transfer RNA (tRNA)?

A

Transfer RNA (tRNA)
• Found in the cytoplasm.
• It has an amino acid binding site at one end and a sequence of three bases at the other end called an anticodon.
• It carries the amino acids that are used to make
proteins to the ribosomes during translation.

42
Q

What is Ribosomal RNA (rRNA)?

A

Ribosomal RNA (rRNA)
• Forms the two subunits in a ribosome (along with proteins).
• The ribosome moves along the mRNA strand during protein
synthesis. The rRNA in the ribosome helps to catalyse the
formation of peptide bonds between the amino acids.

43
Q

What is the genetic code?

A

1) The genetic code is the sequence of base triplets (codons) in DNA or mRNA,
which codes for specific amino acids.
2) 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 — the code is non-overlapping.
3) The genetic code is also degenerate — there are more possible combinations of triplets than there
are amino acids (20 amino acids but 64 possible triplets). This 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.
4) Some triplets are used to tell the cell when to start and stop production of the protein — these are
called start and stop signals (or start and stop codons). They’re found at the beginning and end of the
gene. E.g. UAG is a stop signal.
5) The genetic code is also universal — the same specific base triplets code for the same
amino acids in all living things. E.g. UAU codes for tyrosine in all organisms.

44
Q

What is the first stage of protein synthesis?

A

Transcription

45
Q

What is the first step of transcription?

A

During transcription an mRNA copy of a gene
(a section of DNA) is made in the nucleus:
1) Transcription starts when RNA polymerase
(an enzyme) attaches to the DNA double-helix
at the beginning of a gene.

46
Q

What is the 2nd step of transcription?

A

2) The hydrogen bonds between the two DNA strands
in the gene break, separating the strands, and the
DNA molecule uncoils at that point.

47
Q

What is the 3rd step of transcription?

A

3) One of the strands is then used as a template

to make an mRNA copy.

48
Q

What is the 4th step of transcription?

A

4) 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 strand (except the base T is replaced by U in RNA).

49
Q

What is the 5th step of transcription?

A

5) Once the RNA nucleotides have paired up with
their specific bases on the DNA strand they’re
joined together, forming an mRNA molecule.

50
Q

What is the 6th step of transcription?

A

6) The RNA polymerase moves along
the DNA, separating the strands and
assembling the mRNA strand.

51
Q

What is the 7th step of transcription?

A

7) The hydrogen 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.

52
Q

What is the 8th step of transcription?

A

8) When RNA polymerase reaches a stop codon
(see previous page) it stops making mRNA
and detaches from the DNA.

53
Q

What is the 9th step of transcription?

A

9) 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 (see next page).

54
Q

Second Stage of Protein Synthesis?

A

Translation

55
Q

Whats the 1st stage of translation?

A

Translation occurs at the ribosomes in the cytoplasm. During translation, amino acids are joined together to
make a polypeptide chain (protein), following the sequence of codons carried by the mRNA.
1) The mRNA attaches itself to a ribosome and transfer RNA (tRNA) molecules carry amino acids to the ribosome.

56
Q

Whats the 2nd stage of translation?

A

2) 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.

57
Q

Whats the 3rd stage of translation?

A

3) A second tRNA molecule attaches itself to the next codon on the mRNA in the same way.

58
Q

Whats the 4th stage of translation?

A

4) Ribosomal RNA (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.

59
Q

Whats the 5th stage of translation?

A

5) 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.

60
Q

Whats the 6th stage of translation?

A

6) This process continues, producing a chain of linked amino acids (a polypeptide chain),
until there’s a stop codon on the mRNA molecule.

61
Q

Whats the 7th stage of translation?

A

7) The polypeptide chain moves away from the ribosome and translation is complete.

Biology (9 decks)

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