DNA Flashcards
Understand the deoxyribonucleic acid (DNA) is a double stranded molecule that occurs bound to proteins in chromosomes in the nucleus and as undond circular DNA in cytosol of prokaryotes and the mitochondria and chloroplasts of Eukaryotic cells.
DNA is found in the Cytosol of a prokaryotic cell
DNA is found in the nucleus and mitochondria of a Eukaryotic cell
Recall structure of DNA
DNA stands for Deoxyribonucleic acid
explain the role of helicase and DNA polymerase in the process of DNA replication
Replication of DNA:
Step 1: Double helix unzips and the pair of nucleotides become separated.
Step 2: Bases of nucleotides are exposed to the nucleus which contains many already formed nucleotides.
Step 3: Free nucleotides align with the DNA molecule and hydrogen bonds from between the new nucleotide pair.
DNA Helicase: An enzyme that unwinds the double helix by breaking the hydrogen bonds between the complementary bases.
DNA Polymerase: Enzyme that:
1. replicates the DNA strand by adding complementary nucleotides
2. Proof reads the new strand for errors
3. repairs the new strand if errors are found
Recognise the role of homologous chromosomes, describe the processes of crossing over and recombination and demonstrate how they contribute to genetic variation. Compare and contrast the process of spermatogenesis and oogenesis.
Explain meiosis, meiosis I and meiosis II
Meiosis: The process by which haploid sperm and egg cells (gametes) are made from diploid parent cell.
Meiosis I: Pairs of bivalent chromosomes exchange segments of DNA before being separated into two diploid daughter cells. Meiosis I is similar to the process of mitosis with the additional step of crossing over in order to allow recombinant gametes to be produced.
Meiosis II: once the diploid germ cells have undergone crossing over replication in meiosis I, the process of creating haploid gametes can begin. In order to reduce the number of chromosomes by half, the steps of meiosis I are repeated
demonstrate how the process of independent assortment and random fertilisation alter the variation in the genotype of offspring.
Define the terms genome and gene
Genes are the molecular codes for physical and chemical characteristics of all living organisms, determining which proteins are produced and where and when they are produced.
The genome of an organism is the complete set of all gene-containing chromosomes an individual carries in its cells
Explain Spermatogenesis and oogenesis
Spermatogenesis: Meiosis in human males produce sperm cells and occurs within the test in the seminiferous tubules. A diploid cell that undergoes meiosis to produce sperm in males is called a spermatogonium. Spermatogenesis begins when spermatogonia undergo mitotic division into diploid cells called spermatocytes. The diploid spermatocytes then undergo meiotic division resulting in four haloid spermatid cells. Sertoli cells nourish the spermatids during their maturation into spermatozoa.
Oogenesis: Meiosis in Human Females produce ova (egg cells) and begins within the ovaries of the developing female foetus. The diploid cells that undergo meiosis to produce ova in females are called oogonia. Oogenesis begins when oogonia undergo mitotic division into diploid cells called primary oocytes. The diploid primary oocytes then undergo meiotic division in meiosis I, producing a haploid secondary oocyte and haploid polar body. The polar body degenerates while the secondary oocyte progresses through meiosis II to produce an ovum for release during ovulation.
Understand coding and noncoding.
Nucleic acid molecules contain genetic codes for the production of proteins. The code is contained in a nucleotide triplet referred to as a codon. Each codon corresponds to an amino acid or to instructions to stop or start the process of translation. Some sections of DNA between genes do not code for amino acids or instructions, and are therefore not used to construct proteins. These sections are referred to as noncoding DNA.
Explain the process of protein synthesis in terms of:
- transcription of a gene into messenger RNA in the nucleus
- translation of mRNA into an amino acid sequence at the ribosome
Transcription: is a process that occurs in the nucleus of eukaryotic cells. It allows single-stranded messenger RNA (mRNA) molecules to be produced from a double-stranded DNA molecule. Transcription can be broken into three stages: Initiation, elongation and termination.
Translation: Ribosomes in the soma of a eukaryotic cell build a polypeptide chain from amino acids by translating mRNA codons.
Explain the different stages of Transcription (initiation, elongation and termination):
Initiation: Assisted by special proteins called transcription factor, RNA polymerase unzips the DNA double helix by breaking the weak hydrogen bonds between nitrogenous bases. This exposies the bases, allowing them to bind with free-floating nucleotides during the second step of transcription.
Elongation: Across a section of approximately 12-14 base pairs called a transcription bubble, RNA polymerase begins to produce an mRNA strand. The DNA strand acts as a template, which the RNA polymerase moves along adding corresponding nucleotides through the process of complementary base pairing. New nucleotides are added to the 3’ end of the growing mRNA strand since synthesis occurs in the 5’ to 3’ direction. Synthesis of mRNA follows the same base pairing as DNA replication, with the exception of adenine, which pairs with uracil instead of thymine in RNA.
Termination: A stop codon signals the RNA polymerase to cease transcription and terminate the mRNA molecule.
Explain the three stages of translation (initiation, elongation and termination)
Initiation: A ribosomal subunit attaches itself and moves along an mRNA strand in 5’ to 3’ direction until it recognises a start codon (AUG). A free-floating transfer RNA (tRNA) molecule with the anticodon UAC carrying methionine attaches to the mRNA start codon. The ribosome is now ready to begin translating the mRNA into a polypeptide chain.
Elongation: As the ribosome progresses along an mRNA strand, it reads the codons and matches them with the anticodon of nearby tRNA molecules. As each tRNA anticodon binds with its corresponding mRNA codon it releases its amino acid, which joins the growing polypeptide chain through a condensation polymerisation reaction.
Termination: The process of elongation continues until the ribosome reads a stop codon and releases the polypeptide chain into the cytoplasm of the cell. The free-floating polypeptide chain then moves to the endoplasmic reticulum or the Golgi apparatus where it will undergo further processing to become a functional protein.
Identify the different type of mutations
Mutations during DNA replication:
Mutations occur during DNA replication when an error is made by adding, omitting or incorrectly matching a free-floating nucleotide to the exposed DNA strand. Mutations to the DNA sequence during replication may result in a variety of changes to proteins produced, with some outcomes having little or no effect on the organism and others having catastrophic effects on the organism.
Point Mutations:
Changes to a single nitrogenous base in a DNA sequence is called a point mutation. A change to one of the three bases in a DNA codon changes amino acids added to the polypeptide chain produced by the ribosome.
Somatic Mutations:
Mutations within somatic cells occuring during mitotic cell division only affect the individual since somatic cells and their DNA are not passed on to off spring.
Inherited Mutations:
are those occurring in germ line cells (sperm and egg), which are passed on to offspring
Non-disjunction:
Occurs when spindle fibres fail to sperate chromatids during anaphase. This can occur during anaphase of meiosis I, Meiosis II or mitosis. The daughter cell formed after non-disjunction have an abnormal number of chromosomes. This is referred to as aneuploidy.
Explain Karyotypes
A karyotype is an image of an individual organism’s complete set of chromosomes in their homologous pairs arranged in order of size and centromere location. Scientists obtain the chromosomes of a single cell from an organism and arranging them in a karyotype, this allows changes in the number or structure of chromosomes to be identified.
What are Alleles, Genotypes, phenotypes, punnett squares
- Alleles are different versions if genes, and they can be dominant or recessive
- Genotype describes the alleles an individual carries and phenotype describes the trait expressed
- punnett squares can be used to determine the percentage of genotypes and phenotypes the offspring of parents with different combinations of alleles will have.
