DNA Flashcards
what is the structure of DNA?
- found within the nucleus of cells.
- a double helix,
- a phosphate molecule, a sugar molecule, and a nitrogenous base.
- Nitrogenous bases = cytosine, guanine, adenine, and thymine
what is a histone?
protein molecule around which DNA is tightly coiled to form chromatin
what is chromatin?
Tangled network of coiled DNA in a cell that is not dividing.
what is a chromosome?
Super coiled chromatin when a cell divides
what is the process of DNA replication?
- DNA double helix unwinds
- DNA helicase- unzips by the weak hydrogen bonds between bases breaking
- DNA polymerase-Free nucleotides pair up with exposed DNA bases.
- Work in a 5’ to 3’ direction
- Weak hydrogen bonds form between the complementary bases
- DNA ligase- helps build the strands and attach the nucleotides to each other.
- 2 identical daughter molecules are formed
- 1 old strand and 1 new strand
- This is Semi-conservative replication
what is protein synthesis?
the process in which cells make proteins
what is transcription?
DNA is copied
describe the process of transcription?
- occurs in the nucleus
- mRNA is made which is initiated at the promoter region of DNA on the template strand
- Free bases in nucleus are brought to DNA and the complementary bases are built using RNA polymerase
- mRNA is made from the template strand and leaves the nucleus through nuclear pores.
- Thymine is replaced by Uracil
describe the process of translation
what is translation?
Production of a protein using the information that is coded in the mRNA molecule
describe translation
- mRNA attaches to a ribosome. Ribosome recognizes the initiation codon AUG
- tRNA which has anti-codon complementary to AUG attaches to the mRNA and carries an amino acid
- The next codon is read and the matching anticodon of the tRNA is attached
- Amino acids join via peptide bonds and the growing polypeptide chain is removed from the tRNA’s
- When a stop codon is reached translation stops and the polypeptide (protein) is released
- Protein is released from the ribosome
- Empty tRNA can be recycled
describe mtDNA
- Mitochondria
- Relatively small
- Circular
- Inherited only form the mother
- Not bound to histones
describe nDNA
- Nucleus
- Much larger
- Double helix
- Inherited from both mother and father
- Wrapped around histones
what is epigenetics?
The altering of a gene without changing the gene structure
what are the two processes of modifying the histone proteins?
acetylation and methylation
what factors affect Epigenetics?
stress, diet, age, lifestyle
factors don’t change DNA, yet interfere with transcription and translation processes involved in protein production
what is gene expression?
the process where information in the gene is used to make a product
what is acetylation?
Addition of acetyl group to a histone
= Enhances gene expression as transcription is promoted by allowing access to RNA polymerase due to the reduced attraction between DNA and histones, causing chromatin structure to relax
what is methylation?
Addition of methyl group to histone
- Occurs at CpG sites (cytosine is adjacent to guanine)
- Inhibits gene expression by restricting access to RNA polymerase as DNA is more tightly coiled around histone molecules
what is the cell cycle?
- The events that take place from one cell division to the next
what are the phases of the cell cycle?
- G1 phase: The first gap, or growth phase, of the cell cycle
- S phase: The synthesis phase of the cell cycle; the portion of interphase during which DNA is replicated
- G2 phase: The second growth phase of the cell cycle, involves preparation for cell division and checks new chromosomes for errors.
- M phase: The phase of the cell cycle that includes mitosis and cytokinesis.
- G0 phase: Nondividing stage
describe mitosis
- Function: for growth and repair of the body
- Interphase = Before mitosis starts the parent cell replicates DNA
- Prophase = chromosomes condense and become visible, sister chromatids form pairs
- Metaphase = Membrane surrounding nucleus breaks down, chromosomes line up along the equator of the cell
- Anaphase = Spindle fibers attach to centromeres and pull apart sister chromatids as they contract towards the centrioles, at opposite poles of the cell
- Telophase: New nuclear membrane assembles around the two sets of chromosomes
what is differentiation?
process in which cells become specialised in structure and function
what are the properties of stem cells?
self renewal-ability to divide many times while maintain an unspecialised state, potency-ability to differentiate into specialized cells.
what are multipotent cells?
Cells capable of giving rise to more than once cell type, but only a few types. (limited number)
= bone marrow stem cells
what are pluripotent cells?
Cells capable of giving rise to most different cell types
(any cells of the body, except extra-embryonic cells)
= placenta
what are totipotent cells?
Cells capable of giving rise to any cell type (all)
= e.g. zygote (unfertilized egg)
what is cancer?
uncontrolled cell growth
what is a tumor?
Mass of abnormal cells formed from uncontrollable cell growth
what is a malignant tumour?
Tumour cells can invade tissues and spread to other parts of the body
what is metastasis?
When tumour cells have spread to other parts of the body to form secondary tumours
what are benign tumours?
Tumour cells that do not invade tissues and do not spread to other parts of the body
what is apoptosis?
Cell suicide-programmed cell death
what are carcinogens?
Agents capable of causing cancer = UV rays = x rays = ionising radiation = viruses = chemical carcinogens.
what test is used to detect cervical cancer?
Pap smear
what test is used to detect breast cancer?
mammogram
what test is used to detect bowel cancer?
faecal occult blood test (FOB)
what test is used to detect prostate cancer?
digital rectal examination, prostate-specific antigen blood test and biopsy.
describe meiosis
- Function: to produce gametes
- Two divisions
Prophase 1: chromosomes condense, homologous chromosomes pair up and spindle fibres start to form. Crossing over occurs.
Metaphase 1: Nuclear envelope dissolves, bivalents (pair of homologous chromosomes) line up along the cell’s equator.
Anaphase 1: Disjunction-Separation of bivalents, maternal and paternal chromosomes move to opposite poles of the cell.
Telophase 1: Spindle fibres segregating the bivalents dissolve, chromosomes de-condense, cytokinesis occurs.
= Results in four unique daughter cells each with half the number of chromosomes as the parent.
what is crossing over?
- Chromatids may cross break and exchange segments
- Prophase 1
- New combinations of genes (recombination) so that the chromosomes passed on to the offspring are not exactly the same as those inherited by the parent
what is independent assortment?
- Tetrads can align in the equator of the cell in a number of different combinations.
- Maternal or paternal homologous chromosomes can be on the left or the right of each other
- Metaphase 1
- The random combination of alleles due to allele pair separating independently of one another
what is non-disjunction?
- When one or more of the chromosome pairs fail to separate during meiosis.
- Anaphase 1 and 11
- Results in one of the daughter cells receiving an extra chromosome and the other daughter cell lacking that chromosome. The resulting gametes will either have 24 chromosomes or 22 chromosomes instead of the normal 23.
what is down syndrome?
= trisomy 21
- Extra copy of chromosome 21
- Resulting in characteristic facial appearance, variable degrees of intellectual disability and physical abnormalities
what is monosomy?
Individual has only one copy of a chromosome instead of two
what is trisomy?
An individual has an extra chromosome
what is partial monosomy?
Individual has part of a chromosome missing
what is partial trisomy?
Individual has part of an extra chromosome
compare mitosis and meiosis
Mitosis function For growth and repair location = All somatic cells of the body number of divisions = 1 number of daughter cells produced = 2 nature of daughter cells = Diploid & Genetically identical
meiosis Purpose = production of gametes Location = gonads (ovaries and testes) Number of divisions = 2 Number of daughter cells produced = 4 Nature of daughter cells = haploid & genetically different
