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A2 Biology Unit 5 > DNA and RNA > Flashcards

Flashcards in DNA and RNA Deck (26):

What does RNA, mRNA and tRNA stand for?

Ribonucleic acid, messenger ribonucleic acid and transfer ribonucleic acid


Define codon

A sequence of three adjacent nucleotides in mRNA that codes for one amino acid.


Define stop codon

A codon that tells the ribosome to stop adding amino acids to the protein.


Define non-overlapping

Each base in the sequence is read only once


Define degenerate

More than one codon codes for the production of one amino acid.


Define universal

Same codon codes the same amino acid in all organisms.


What type of chain is DNA, mRNA and tRNA?

DNA- Double polynucleotide chain

mRNA- Single polynucleotide chain

tRNA- Single polynucleotide chain


What is the size order of mRNA, DNA and tRNA?



What type of shape is DNA, mRNA and tRNA?

DNA- Double helix molecule

mRNA- Single helix molecule

tRNA- Clover shaped


What is the pentose sugar in DNA, mRNA and tRNA?

DNA- Deoxyribose

mRNA- Ribose

tRNA- Ribose


What are the organic bases in DNA, mRNA and tRNA?

DNA- adenine, guanine, cytosine and thymine

mRNA- adenine, guanine, cytosine and uracil

tRNA- adenine, guanine, cytosine and uracil


Where is DNA, mRNA and tRNA found?

DNA- found mostly in the nucleus

mRNA- forms in the nucleus and leaves via pores in the nuclear envelope and enters the cytoplasm.

tRNA- formed in the nucleus but found around the cell.


What is the quantity of DNA, mRNA and tRNA?

DNA- Quantity is constant for all cells of a species

mRNA- Quantity varies from cell to cell and with level of metabolic activity

tRNA- Quantity varies from cell to cell and with level of metabolic activity


What is the stability of DNA, mRNA and tRNA?

DNA- Chemically very stable

mRNA- Chemically unstable- easily broken down

tRNA- More stable than mRNA but less than DNA.


What is the structure of a nucleotide?

Each nucleotide is made from a phosphate group, a pentose sugar (with 5 carbon atoms) and a nitrogenous base.


What are polynucleotide strands?

Many nucleotides join together to form the polynucleotide strands.
The nucleotides join up between the phosphate group of one nucleotide and the sugar of another, creating a sugar phosphate backbone.


What is specific base pairing?

Two DNA polynucleotide strands join together by hydrogen bonds between the bases.
Each base can only join with one particular partner (specific base pairing).
A-T and G-C


What are genes?

Genes are sections of DNA found on chromosomes.
Genes code for proteins (polypeptides)- they contain the instructions to make them.
It's the order of nucleotide bases in a gene that determines the order of amino acids in a particular protein.


Where are DNA molecules found?

In the nucleus of the cell.


What is transcription?

DNA is too larger to move out of the nucleus, so a section is copied into a molecule called mRNA.


What is translation?

When the mRNA leaves the nucleus and joins with a ribosome in the cytoplasm, where it can be used to synthesise a protein.


What is the structure of RNA?

Like DNA, it's made up of nucleotidees that contain one of four different bases. The nucleotides also form a polynucleotide strand with a sugar phosphate backbone. But RNA differs from DNA in these ways:
- The sugar in RNA is a ribose sugar (not deoxyribose)
- The nucleotides form a single polynucleotide strand (not a double one)
- Uracil (U) replaces thymine as a base. Uracil always pairs with adenine during protein synthesis.


What bonds hold the tRNA in its clover shape?

Hydrogen bonds


Where does the synthesis of proteins take place?

The cytoplasm- sections of the DNA code are transcribed onto a single stranded molecule called RNA.


What is mRNA?

The RNA that transfers the DNA code from the nucleus to the cytoplasm because it is small enough to leave the nucleus through the nuclear pores and to enter the cytoplasm.


What are the main features of the genetic code?

Each amino acid is coded for by a sequence of three nucleotide bases on mRNA (i.e a codon).
A few amino acids have only a single codon.
The code is a degenerate code- most amino acids have more than one codon.
Three codons do not code for any amino acid. These are called stop codons and mark the end of a polypeptide chain.
The code is non overlapping, that is, each base in the sequence is read only once.
It is a universal code, that is, the same codon codes for the same amino acid in all organisms.