B1. DNA & RNA Flashcards
DNA and RNA function
What are DNA and RNA?
What is DNA used for?
What is RNA used for?
What are ribosomes and how are they linked to RNA?
DNA and RNA are both types of nucleic acid. They’re found in all living cells and they both carry information.
Your DNA (deoxyribonucleic acid) is used to store your genetic information—that’s all the instructions needed to grow and develop from a fertilised egg to a fully grown adult.
RNA (ribonucleic acid) is similar in structure to DNA. One of its main functions is to transfer genetic information from the DNA to the ribosomes. Ribosomes are the body’s ‘protein factories’ - they read the RNA to make polypeptides (proteins) in a process called translation. Ribosomes themselves are made from RNA and proteins.
Nucleotide structure
What do nucleotides consist of?
Molecules of DNA and RNA are polymers of nucleotides. A nucleotide is a type of biological molecule which is made from three different components: a pentose sugar (that’s a sugar with 5 carbon atoms), a nitrogen-containing organic base (organic means that it contains carbon), and a phosphate group
Polynucleotide structure
How are they formed?
What is the chain of phosphates and sugars called?
Many nucleotides join together to form polynucleotide strands (or chains). The nucleotides join up via a condensation reaction between the phosphate group of one nucleotide and the sugar of another. This forms a phosphodiester bond (consisting of the phosphate group and two ester bonds). The chain of phosphates and sugars is known as the sugar-phosphate backbone
What does a nucleotide look like?
Figure 2: Structure of a single polynucleotide strand.
DNA structure
What is the structure?
How are they adapted to their function?
DNA has a double helix structure. This means that a DNA molecule is formed from two separate strands which wind around each other to form a spiral. The strands are polynucleotides. They’re made up of lots of nucleotides joined together in a long chain.
DNA molecules are really long and are coiled up very tightly, so a lot of genetic information can fit into a small space in the cell nucleus.
DNA nucleotide structure
What does it consist of?
What are the possible bases?
A DNA nucleotide is made from a phosphate group, the pentose sugar deoxyribose and a nitrogen-containing organic base.
Each DNA nucleotide has the same sugar and phosphate. The base on each nucleotide can vary though. There are four possible bases - adenine (A), thymine (T), cytosine (C) and guanine (G).
Complementary base pairing
How are different bases joined and which ones?
Two polynucleotide strands are? What does this mean?
Two DNA polynucleotide strands join together by hydrogen bonds between the bases. Each base can only join with one particular partner - this is called complementary base pairing (or specific base pairing). Adenine always pairs with thymine (A-T) and guanine always pairs with cytosine (G-C). This means there are always equal amounts of adenine and thymine in a DNA molecule and equal amounts of cytosine and guanine. Two hydrogen bonds form between A and T, and three hydrogen bonds form between C and G.
The two polynucleotide strands are antiparallel-they run in opposite directions. Two antiparallel strands twist to form a DNA double helix.
Figure 6: The overall structure of a DNA molecule.
RNA structure
Like DNA, RNA is made of nucleotides that contain a sugar, a phosphate
group and one of four different bases. The nucleotides also form a polynucleotide strand with a sugar-phosphate backbone. But the structure of RNA differs from DNA in four main ways:
- The sugar in RNA nucleotides is a ribose sugar (not deoxyribose). It’s still a pentose sugar though.
- Uracil (U, a pyrimidine) replaces thymine as a base. Uracil always pairs with adenine in RNA.
- The nucleotides form a single polynucleotide strand (not a double one).
- RNA strands are much shorter than most DNA polynucleotides.
DNA vs RNA comparison
