A Level Biology - Nucleotides and Nucleic Acids

How many hydrogen bonds form between adenine and thymine?

2

State step 2 of DNA purification when using the precipitation reaction:

2) Make up a solution of detergent ( a dilute washing-up liquid will do), salt (sodium chloride) and distilled water.

How many hydrogen bonds form between guanine and cytosine?

3

What is complementary base pairing?

Complementary base pairing is where each base can only join with one particular base.

How can DNA be purified?

DNA can be purified using a precipitation reaction.

Why does DNA replicate?

DNA copies itself before cell division so that each new cell has the full amount of DNA. This is important for making new cells and for passing genetic information from generation to generation.

What do RNA nucleotides contain?

RNA (ribonucleic acid) contains nucleotides with a ribose sugar. Like DNA, an RNA nucleotide also has a phosphate group and one of four different bases. In RNA, uracil replaces thymine as a base. An RNA molecule is made up of a single polynucleotide chain.

What is RNA?

RNA is a single polynucleotide strand and it contains uracil (U) as a base instead of thymine (T). Uracil always pairs with adenine during protein synthesis. However there are different types of RNA.

What is RNA used for?

RNA is used to make proteins from the instructions in DNA

What do DNA nucleotides contain?

The nucleotides in DNA all contain the same pentose sugar called deoxyribose. Each DNA nucleotide also has the same phosphate group. The base on each nucleotide can vary though. There are four possible bases - adenine (A), thymine (T), cytosine (C) and guanine (G).

How do the nucleotides join up?

The nucleotides join up between the phosphate group of one nucleotide and the sugar of another. This forms a phosphodiester bond which consists of the phosphate group and two ester bonds.

State the last step of translation

The polypeptide chain (protein) then moves away from the ribosome and translation is complete.

What determines which protein is made?

The sequence of amino acids. The order of nucleotide bases in a gene determine the order of amino acids in a particular protein.

Which bases are pyrimidines?

cytosine, thymine, uracil

State step 1 of DNA purification when using the precipitation reaction:

1) Break up the cells in your sample. This can be done by using a blender for about 10seconds.

How is DNA replicated?

1) DNA helicase (an enzyme) breaks the hydrogen bonds between the two polynucleotide DNA strands. The helix unzips to form two single strands. 2) 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 G with C. 3) The nucleotides on 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. Each new DNA molecule contains one strand from the original molecule and one new strand.

State step 3 of DNA purification when using the precipitation reaction:

3) Add the broken-up cells to a beaker containing the detergent solution.

State step 4 of DNA purification when using the precipitation reaction:

4) Incubate the beaker in a water bath at 60 degrees celsius for 15 minutes Whilst it is in the water bath, the detergent in the mixture breaks down the cell membranes. The salt then binds to the DNA and causes it to clump together. The temperature of the water bath should be high enough to stop enzymes in the cells from working properly and breaking down the DNA.

State step 5 of DNA purification when using the precipitation reaction:

5) Once incubated, put your beaker in an ice bath to cool the mixture down.

State step 6 of DNA purification when using the precipitation reaction:

6) When the mixture's cool, filter the mixture using coffee filter paper and a funnel. Transfer a sample of your filtered mixture to a clean boiling tube and discard the contents of the filter paper.

State step 7 of DNA purification when using the precipitation reaction:

7) Add protease enzymes to the filtered mixture. These will break down some proteins in the mixture, e.g. proteins bound to the DNA.

State step 8 of DNA purification when using the precipitation reaction:

8) Slowly dribble some cold ethanol don the side of the tube, so that it forms a layer on the top of the DNA-detergent mixture.

State step 9 of DNA purification when using the precipitation reaction:

9) If you leave the tube for a few minutes, the DNA will form a white precipitate, which can be removed from the tube using a glass rod.

A Level Biology - Nucleotides and Nucleic Acids

A Level Biology - Nucleotides and Nucleic Acids

What is a gene?

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.

What is a nucleotide?

A nucleotide is a type of biological molecule

What is the difference between a purine base and a pyridine base?

A purine base contains two carbon-nitrogen rings joined together, whereas a pyrimidine base only has one carbon-nitrogen ring. This means that a pyrimidine base is smaller than a purine base.

State step 2 of translation

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.

State step 4 of translation

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

What does ATP contain?

ATP contains the base adenine, the sugar ribose and three phosphate groups.

What does the base adenine always pair with when in the DNA structure?

Adenine (A) always pairs with Thymine (T)

Which bases are purines?

Adenine and Guanine

Which elements do all nucleotides contain?

All nucleotides contain the elements carbon , hydrogen, oxygen, nitrogen and phosphorous

How can polynucleotides be broken down into nucleotides?

By breaking the phosphodiester bonds.

What is DNA composed of?

DNA is composed of two polynucleotide strands joined together to form a double-helix shape.

Why is a section of DNA copied into mRNA and what is the process called?

DNA is too large to move out of the nucleus, so a section is copied into mRNA. This process is called transcription.

What is DNA used for?

DNA is used to store genetic information - the instructions an organism needs to grow and develop.

What is the sugar present in DNA called?

Deoxyribose sugar

How many bases code for an amino acid?

Each amino acid is coded for by a sequence of three bases (called a triplet) in a gene. Different sequences of bases code for different amino acids.

What happens when a cell needs energy?

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.

What does the base guanine always pair with?

Guanine (G) always pairs with cytosine (C)

Why do scientists often need to extract a pure DNA sample from cells?

In order to analyse it

How do plants make ATP?

In respiration, the energy released is used to make ATP and then molecules of ATP provide energy for chemical reactions in the cell. ATP is synthesised from ADP and inorganic phosphate . The ADP is phosphorylated to form ATP and a phosphate bond is formed.

The two polynucleotide strands are anti parallel, what does anti parallel mean?

It means that they run in opposite directions

What are nucleotides made from?

Nucleotides are made from: a pentose sugar (sugar with 5 carbon atoms), a nitrogenous base and a phosphate group.

When nucleotides join together, what do they form?

Polynucleotides

What are the two types of base present in DNA and RNA nucleotides?

Purines and pyrimidines

What is the sugar present in RNA called?

Ribose

State step 3 of translation

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.

What are the organisms called that make the proteins for DNA and where are they found?

Ribosomes make the proteins and they are found in the cytoplasm.

Some triplets are used for coding, but what are they also used for?

Some triplets can be used to tell the cell when to stop production of a protein - these are called stop signals and they are found at the end of the mRNA. For example, UAG is a stop signal.

State step two of how an mRNA copy of a gene is made in the nucleus

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). Once the RNA nucleotides have paired up with their specific bases on the DNA srand, they're joined together by RNA polymerase, forming an mRNA strand.

State step three of how an mRNA copy of a gene is made in the nucleus

The RNA polymerase moves along the DNA, assembling the mRNA strand. 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.

What does ADP contain?

The base adenine, the sugar ribose and two phosphate groups.

What is the chain of sugars and phosphates known as?

The chain is known as the sugar-phosphate backbone

What are DNA and RNA essential for?

The function of living organisms

What else can the genetic code also be described as?

The genetic code is also degenerate as 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. Not all triplets code for amino acids though.

What else can the genetic code be described as?

The genetic code is also universal - this means that the same specific base triplets code for the same amino acids in all living things, e.g. UAU codes for tyrosine in all organisms.

What is the genetic code?

The genetic code is the sequence of base triplets (codons) in DNA or mRNA, which codes for specific amino acids. 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.

State step 1 of translation

The mRNA attaches itself to a ribosome and transfer RNA (tRNA) molecules carry amino acids to the ribosome

How do the two polynucleotide strands join together?

The tow strands join together by hydrogen bonding between the bases

What signals are found at the start of the mRNA?

There are also start signals which are found at the start of the mRNA and they tell the cell when to start protein production, but these code for a specific amino acid called methionine.

What are ADP and ATP?

They are phosphorylated nucleotides

Why are nucleotides really important?

They are really important, because they are the monomers that make up DNA and RNA. There also special types of nucleotides, such as ADP and ATP. They're used to store and transport energy in cells.

What is transcription?

Transcription is the first stage of protein synthesis. During transcription an mRNA copy of a gene (a section of DNA) is made in the nucleus.

State step one of how an mRNA copy of a gene is made in the nucleus

Transcription starts when RNA polymerase (an enzyme) 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, and the DNA molecule uncoils at that point. One of the strands is then used as a template to make an mRNa copy.

What is translation?

Translation is the second stage of protein synthesis . It takes place at the ribosomes in the cytoplasm. During translation, amino acids are joined together by a ribosome to make a polypeptide chain (protein), following the sequence of codons carried by the mRNA.

State step four of how an mRNA copy of a gene is made in the nucleus

When RNA polymerase reaches a stop codon, it stops making mRNA and detaches from the DNA. The mRNA moves out of the nucleus through a nuclear pore and attaches to a ribosome in the cytoplasm, where in the next stage of protein synthesis takes place.

What happens when the mRNA leaves the nucleus and what is the process called?

When the mRNA leaves the nucleus, it joins with a ribosome in the cytoplasm, where it can be used to synthesise a protein. This process is called translation.

How do you phosphorylate a nucleotide?

You add one or more phosphate groups to it.

What is the function of mRNA?

mRNA carries the genetic code from the DNA in the nucleus to the cytoplasm, where it is used to make a protein during translation. In mRNA, groups of 3 adjacent bases are usually called codons.

What is messenger RNA?

mRNA is a single polynucleotide strand. It is made in the nucleus during transcription.

What are DNA and RNA?

nucleic acids

Where are DNA molecules found?

nucleus

What is ribosomal RNA (rRNA)?

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.

What is transfer RNA (tRNA)?

tRNA is a single polynucleotide strand that's folded into a clover shape. Hydrogen bonds between specific base pairs hold the molecule in this shape. Every tRNA molecule has a specific sequence of three bases at one end called an anticodon. They also have an amino acid binding site at the other end. tRNA is found in the cytoplasm where it's involved in translation. It carries the amino acids that are used to make proteins to the ribosomes.