Biology: Nucleic Acids are Important Information Carrying Molecules Flashcards
DNA and RNA
Deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) are important information - carrying molecules. In all living cells, DNA holds genetic information and RNA transfers genetic information from DNA to the ribosomes.
Structure of DNA and RNA
Both DNA and RNA are polymers of nucleotides. Each nucleotide is formed from a pentse, a nitrogen - containing organic base and phosphate group
DNA and RNA
The components of a DNA nucleotide are deoxyribose, a phosphate group and one of the organic base adenine, cytosine, guanine or thymine
A DNA molecule is a double helix with two polynucleotide chains held together by hydrogen bonds between specific complementary base pairs.
DNA replication
The semi-conservative replication of DNA ensure genetic continuity between generations of cells
How does the structure of DNA relate to its function?
DNA is a double stranded molecule, it is made from two polynucleotide strands that are joined together via hydrogen bonding between the bases of opposite nucleotides. DNA forms the genetic code of living things. The sequence of the nitrogenous bases forms the code with a triplet of bases coding for a single amino acid, and the length of triplets coding for one protein being a gene. The nucleotides in a strand are held together with strong phosphodiester bonds between the sugar unit of one nucleotide and the phosphate group of another. These strong bonds maintain the integrity of the backbone as it prevents nucleotides breaking away and rejoining in a different sequence.
DNA has to be replicated when new cells are formed in Mitosis. The DNA structure enables identical copies to be produced. The two polynucleotide strands are held in play weak hydrogen bonds that an be broken to allow both strands to separate and act as templates for the productions of new strands. The nucleotides can only base pair with completely base from other nucleotides. Adenine pairs with thymine and cytosine pairs with Guanine. This complementary base pairing maintains the sequence of base so that identical copies of the DNA are made. The DNA coils into a helix shape that means that a large amount of genetic material can be contained within the Nucleus.
Structure of DNA
Phosphate group
Nitrogenous base
Pentose sugar - deoxyribose
Strong covenant bonds between the phosphate group and pentose sugar
MAny of these creates a the sugar phosphate backbone
4 different type of bases that are complementary to a specific different complementary base - specific complementary base pairing
Adenine (2 hydrogen bonds) Thymine
Cytosine (3 hydrogen bonds) Guanine
Anti-parallel strands
Stages of Mitosis
Interphase before Mitosis:
The cell enlarges
Organelles replicate
New proteins are synthesised
The DNA is replicated to produce chromosomes that consist of two sister chromatids joined by a centromere
Prophase:
The chromosomes condense and become visible
Nuclear membrane begins to break down
The spindles begin to form
Metaphase:
The nuclear membrane completely breaks down
Spindles full form
The chromosomes line up individually are the equator and are attached to the spindles at the centromere
Anaphase:
The sister chromatids of each chromosome is pulled apart
They are pulled apart by the centromere as the spindles contract
The chromatids are pulled to opposite poles
Telophase:
The spinels break down
Nuclear membrane reforms
The chromosomes decondense
Cell membrane forms down the centre of cell
Two daughter cells are produced
Homologous chromosomes
A pair of matching chromosomes, with the same genes in the same loci but each chromosome may have a different allele of a gene. One chromosome is maternal and the other is parental.
Cancer: Benign
Tumor cells that stay in the place where they were formed
Cancer: Malignant
Tumor cells that travel in the blood from where they were formed to other parts of the body where they cause new tumours
Cancer: Metastasis
The migration (movement) of cancer cells to other parts of the body to form new tumours
Cancer: Proto-oncogene
Code for proteins that stimulate cell division and inhabit cell death
Cancer: Oncogene
Mutated forms of Proto-oncogene stimulate cell division because they can’t be inhibited by tumour suppressor genes
Cancer: Tumour-suppressor gene
Code for proteins that prevent cell division or cause cell death
Cancer
- Cancer is cells that represent divide (it is uncontrolled cell division)
- The cancer can be benign - the cells stay where they are
- The threat of benign tumours is that growth compresses other functional body tissues and stops them from working correctly
- Malignant cancer cells enter the bloodstream and spread through the body. New tumours form where the cells move to.
- The process of malignant cancer cells spreading is called metastasis
- Happens when the control mechanisms for cell division and cell death fail.
- Two groups of genes control the cell cycle - Proto-oncogene and tumour suppressor genes
- Proto-oncogenes stimulate cell division to occur or they prevent cell death
- Tumour-suppressor genes prevent cell division or they prevent cells death
- Cancer occurs when mutations occur in genes
- Oncogenes result in cell division because the proteins produced from Tumour-suppressor genes cannot inhibit the oncogenes
- Tumour suppressor genes can mutate so that the protein they produced does not act on Proto-oncogenes to inhibit them. Therefore cell division continues
- Cancer is more likely to occur as you get older because more mutations will have occurred
- Chemotherapy - drugs that affect the cell cycle so that cell division is prevented, or which lead to cell death.
- The drugs can stop DNA replication or inhibit Mitosis
- The drugs are most effective against rapidly dividing cells, so cancer cells are more affected than normal cells
- Side effects are caused by drugs affecting normal cells
- RApidly dividing cells are more likely to be affected I.e hair producing cells which therefore leads to tech typical hair loss
How do tumour suppressor genes and oncogenes affect cell proliferation?
For cancer or tumor to occur there must be at least mutations to 2 genes: the Tumour suppressor gene and the proto-oncogene
Tumour suppressor gene slows down Mitosis
Proto-oncogene - when it is working normally, promotes Mitosis at a normal level —> This could turn into an active oncogene that promotes Mitosis at a too fast rate
What is a mutation?
Change in the base sequence of DNA
Occurs in DNA replication
Occur randomly
Mutagenic agent increase the chances of mutations taking place (e.g. UV light)
Genetic mutation
- Substitution
- Deletion - Results in a frameshift
- Addition - Results in a frame shift
Transcription, Splicing, Translation
- The DNA uncoils and unzips along the length of one gene. This requires DNA helicase
- Hydrogen bonds between nucleotide bases break along the length of one gene and the two strands separate
- Only one strand is used as the template (called the sense strand)
- Free RNA nucleotides complementary base pair with one strand of the DNA
- U pairs with A in the DNA strand and C pairs with G. If T is present in the DNA then it pairs with A.
- RNA polymerase catalyses the formation of the phosphodiester bonds (the sugar-phosphate backbone) that is required to join the nucleotides in the pre-mRNA together
- A molecule of pre-mRNA has formed and this detaches from the sense strand
- The DNA re-coils and re-zips
- The introns are cut out of the pre-mRNA and the Econs are joined together
- This process is called splicing and it produces mRNA
- It only happens in Eukaryotic cells. Prokaryotic DNA does not have introns
- The mRNA moves out of the nucleus via a nuclear pore
- It attaches to the ribosomes. The ribose covers two codons
- The first specific tRNA molecule brings in the first specific amino acid
- The anticodon of the tRNA molecule complementary base pairs with the codon of the mRNA
- A 2nd specific tRNA complementary base pairs with the 2nd codon to bring in the 2nd specific amino acid.
- A Condensation reaction takes place to form a peptide bond between the amino acids. This requires energy from ATP
- The ribose moves on one codon and the first tRNA molecule detaches and moves into the cytoplasm where it can pick up its specific amino acid to be used again. (energy from ATP is required to attach the amino acid to the tRNAs amino acid binding site)
- The third specific tRNA molecule complementary base pairs with the mRNA bringing in the next specific amino acid that will be added to the amino acid chain with a peptide bond
- This process continues until a stop codon is reached. mRNA then detaches from the ribosome and the polypeptide produced can fold into a protein with a 3D shape (tertiary structure)
