Nucleic Acids Flashcards
What does DNA stand for?
Deoxyribonucleic Acid
What is DNA and what is it made up of?
it is a polynucleotide, usually double-standed, made up of multiple repeating nucleotides
What is each nucleotide made up of?
A pentose sugar, deoxyribose (pentagon shape)
A phosphate group (circle shape)
One of 4 possible nitrogen-containing bases (rectangle)
How is a sugar-phosphate backbone formed?
Each nucleotide joins to the next by forming a phosphodiester bond between the phosphate group and a carbon 3 of the next nucleotide in the chain. This is another condensation reaction
What is a nucleotide?
It is a monomer.
How are the two strand in the DNA formed?
An inverse second stand runs parralel to itwith H-bonds between the complementry base pairs. The bonds are always between purine to a pyrimidine
A to T = 2 H-bonds
C to G = 3 H-bonds
what is the shape of DNA?
A double-helix
How is DNA formed and why is the shape of the DNA a double-helix?
Due to the extra H-bonds between the complementary base pairs (A to T, G to C) on two antiparallel DNA polynucleotides leads to the formation of a DNA molecule and the twisting of DNA produces its double-helix shape.
The makeup of the sugars-phosphate backbone is always the same the point of the H-bonds are also the same causing it to become a double-helix in shape
What are the 4 possible nitrogen-containing bases?
The purines:
Adenine (A)
Guanine (G)
The pyrimidines:
Cytosine (C)
Thymine (T)
Which of the bases bond together and what do they form?
A and T both form 2 H-bonds, so they pair up between the 2 strands
C and G form 3 bonds so they always pair up
What is the bonding of the bases called and what does it cause?
This is complimentary base pairing, it joins the 2 strands along the DNA’s length
What are the uses of nucleotides?
Ribonucleic acid (RNA) is used in protein synthesis
Many coenzymes contain nucleotides e.g.
Forming energy-rich molecules by adding multiple phosphate groups:
How is RNA using in protein synthesis
It uses ribose as its pentose sugar instead of the deoxyribose in DNA
Give examples of coenzymes containing nucleotides
NADP in photosynthesis
NAD and FAD in respiration
How do nucleotides form energy rich molecules by adding multiple phosphate groups:
ATP has 3 high-energy phosphate groups attached
They are built up from the energy released in respiration and can be broken down to release that energy to power the activities of the cell
Describe the organisation of the DNA in eukaryotes:
DNA is wound around proteins called histones, forming chromatin.
This chromatin can then coil up for cell division, forming neat chromosomes.
Each chromosome is formed from just one molecule of DNA, tightly coiled.
Most of the DNA is found within the nucleus.
Small loops of DNA without the histone are also found within the mitochondria and chloroplasts
Describe the organisation of the DNA in prokaryotes:
Bacterial DNA is not wound around histones so it is described as naked.
It is also circular, rather than linear, because found in loops.
It is found in the cytoplasm (not enclosed in a nucleus)
What cell division is used to for the replication of DNA?
Mitosis
What must the cell do before it undergoes mitosis?
It must fist copy its DNA at the end of interphase to produce the sister chromatids
Why is it importnt that the new DNA is identical to the parent stand?
Because the daughter cell needs to retain all of the genetic information of the parent cell. Any mistakes in this procedure could lead to mutations that cause diseases such as cancer.
What are the steps in semi-conservative replication?
- The DNA double-helix unwinds, catalysed by gyrase enzyme
- it then unzips, by breaking the H-bonds between the base-pairs, catalysed by DNA helicase enzyme
- Free phosphorylated DNA nucleotides form new H-bonds with their commentary base pairs that are now exposed (A-T, C-G)
- DNA polymerase enzyme then bonds the sugar-phosphate backbones together, using energy released by removing the extra phosphate from the nucleotides
What is the name give to the way our cells replicate and why?
It is called semi-conservative replication as it produces 2 molecules of identical DNA which are made up from one strand of the original DNA and one new strand. The original strand acts as a template to add new, fee nucleotides to cause replication.
How often do errors occur in replication and what occurs when it happens?
Errors in replication occur roughly 1 in 100 million bases, where the wrong base is inserted.
These are mutations which could change the genetic code, although enzymes exist that can correct these mistakes
What is each DNA strand in each human cell made up of?
Around 3 billion nucleotide bases. These are broken up into around 25, 000 genes, which are section of DNA that code for a particular protein
Describe the structure of DNA:
Very long strands Double-stranded Contains bases, A,T, C and G Remains in nucleus Contains deoxyribose
Describe the structure of RNA:
Short-strands Single-stranded Contains A, Uracil (U), C and G Found in nucleus and cytoplasm Contains ribose sugars
What are the steps in protein synthesis?
- Transcription occurs in the nucleus, where the DNA unwinds and unzips, breaking the hydrogen bonds between complementary base pairs to expose a gene
- Free messenger RNA nucleotides (mRNA) form H-bonds with their complementary exposed bases on the template strand (C-G, G-C, A-T, U-A)
- RNA polymerase join their sugar-phosphate backbone together to release a single stranded complementary copy of the gene
- The mRNA leaves through the nuclear pore travels towards the ribosomes
- The mRNA becomes attached at the ribosome, with the use of ribosomal RNA (rRNA), ready to carry out translation
- Transfer RNA (tRNA), from the cytoplasm, brings in an amino acid to match the template found on the mRNA
- These amino acids join with peptide bonds to form the primary structure of proteins. This is an active process requiring energy form ATP
What is the name given to each 3 bases in the DNA?
Triplet, each triplet combination will code for 1 of 20 different amino acids during translation
What happens to the triplet in the DNA as the mRNA takes a complementary copy of the DNA? And what will the tRNA have?
They become 3 base codons
The tRNA will have a complementary anti-codon that will pair up with the codons in translation. Therefore the triplet code on the DNA determines which amino acid joins to the polypeptide chain in what order
What does the sequence in the DNA determine?
The structure of all proteins, each gene codes for one complete protein. Since many proteins are enzymes, this allows the genes within the DNA to regulate the reactions occurring within the cell, giving an organism its characteristics
What is RNA?
Ribonucleic acid is a polynucleotide, usually single stranded, made up of nucleotides containing bases adenine, uracil, cytosine and guanine
What is a gene?
It is a sequence of DNA nucleotides that codes for a polypeptide
