DNA/RNA Structure (2.6, 7.1) Flashcards
What are nucleic acids and what are they made of?
Nucleic acids are the genetic material of the cell and are polymers of nucleotides i.e. made up of repeated nucleotide units.
What is a nucleotide made up of?
A 5C sugar (either ribose or deoxyribose). Drawn as a pentagon.
A phosphate group. Drawn as a circle.
A nitrogen base (guanine, adenine, thymine, cytosine or uracil). Drawn as a rectangle.
DNA
- Name
- Function
- Bonding
- Where it is located
Name: Deoxyribonucleic Acid
Function: It carries the genetic message for the functioning of the organism. A gene is a length of DNA that codes for a polypeptide which forms a protein so DNA codes for the synthesis of proteins.
Bonding: Covalent bonds within nucleotides, weak hydrogen bonds within complementary pairings.
Located: Chromosomes of eukaryotes, nucleoid region of prokaryotes, the mitochondria and in chloroplasts.
What does complementary base pairing refer to?
Adenine will always pair with Thymine (A=T) and Guanine with Cytosine (C≡G).
How was the structure of DNA discovered?
Rosalind Franklin and Maurice Wilkins used X-ray diffraction techniques to identify key properties of the DNA molecule
Wilkins shared this data (without Rosalind’s permission) with James Watson and Francis Crick. Watson and Crick used this data to help construct an accurate model of DNA structure (as a double helix) using paper shapes.
What experiment provided evidence that DNA not protein was the genetic material of the cell?
Alfred Hershey and Martha Chase took viruses and radiolabelled the phosphorus in one and the sulphur in the other. (Phosphorus is present in DNA and sulphur in proteins). These viruses were incubated separately with bacterium. Radioactivity was seen in the bacteria infected with radiolabelled phosphorus (DNA) proving that DNA was the carrier of genetic information not protein.
What does the term ‘anti-parallel’ refer to?
The strands of DNA run in opposite directions. 5’ to 3’ down one strand and 3’ to 5’ down the other.
How does DNA carry genetic information?
DNA carries genetic information in the bases. Three bases (a triplet) codes for an amino acid. As amino acids are the building blocks of proteins the order of the bases codes for proteins.
Give the order of increasing size of DNA:
Yeast
Fruit Fly
Viruses
Bacteria
Human
Viruses
Bacteria
Yeast
Fruit fly
Human
Organisation of Eukaryotic DNA
DNA is wound around eight proteins called histones, forming a nucleosome. The nucleosomes are linked with an additional histone to form a string of chromatosomes. These coil to form a solenoid structure which condenses, forming a 30nm fibre. The fibres form loops, compress and fold around a protein scaffold to form chromatin. Chromatin supercoils during cell division to form chromosomes.
Organisation of Prokaryotic DNA
The DNA is a single, double stranded molecule in the form of a loop or circle.
What are the regions of a DNA strand?
Coding regions (exons) and non-coding regions. Only 1% of the human genome are exons.
What are the regions of DNA that do not code for proteins?
STING
Satellite DNA: repeating sequences of DNA. Highly variable so used in DNA profiling. Called tandem repeats or STRs.
Telomeres: regions of repetitive DNA at the end of chromosomes that protect chromosomes from being damaged during DNA replication. As the cell divides, the telomere shortens until it is too short for cell division to occur.
Introns: non-coding regions within genes.
Non-coding RNA genes: codes for RNA that are not translated to proteins but other molecules such as tRNA.
Gene regulatory sequences: sequences that are involved in transcription.
Describe the differences between RNA and DNA
RNA has…
- Ribose sugar instead of deoxyribose sugar
- Uracil instead of thymine
- Single strand instead of double helix
- Less stable
- Much smaller
What are the three kinds of the RNA molecule?
mRNA (messenger RNA). Nucleus.
- Carries genetic information from the nucleus to the ribosome. Three bases is called a codon.
tRNA (transfer RNA). Cytoplasm.
- Clover leaf shaped molecule. At one end it has a three base code called an anticodon which is complementary to the codon on mRNA and at the other end is an amino acid.
rRNA (ribosomal RNA). Ribosomes.
- Part of the structure of ribosomes (where protein synthesis occurs).