Unit 4 (study buddy) Flashcards
(34 cards)
what does DNA stand for?
Deoxyribonucleic acid
explain the structure of DNA
- double helix
- chain of nucleotides (sugar-phosphate backbone and nitrogenous bases)
- complementary base pairing (A-T, G-C)
- weak, base-specific hydrogen bonds between DNA strands
Explain the role of helicase and DNA polymerase in process of DNA replication
- HELICASE is enzyme that unwinds double helix to separate nucleotide pairs by breaking hydrogen bonds
- DNA POLYMERASE is enzyme that moves along strand, reading, matching, and attaching corresponding free-floating nucleotides
- DNA POLYMERASE only works in 5’ –> 3’ direction
- therefore leading (works in same direction helicase unwinds) and lagging (works in opposite direction to helicase, so does portion, stops, moves to new unwound portion, etc.) strands
describe process of meiosis I and II
MEIOSIS - special type of mitosis that produces gametes
MEIOSIS I:
- PROPHASE I (c’somes condense, homologous c’some pairs align and exchange sections of DNA (crossing over); there are 4 chromatids and 2 chromosomes)
- METAPHASE I (bivalent c’somes align at equator, centrioles produce spindle fibres that attach to centromeres of c’somes)
- ANAPHASE I (spindle fires shorten, pulling away pairs of sister chromatids towards poles, cell elongates)
- TELEPHASE I (c’somes arrive at poles, spindle fibres dissolve, new nuclear membranes form, cytokinesis –> 2 daughter cells)
MEIOSIS II:
- same steps of meiosis I repeated, but:
METAPHASE II (single chromosomes (pair of chromatids) line up in middle)
ANAPHASE II (chromatids pulled apart)
TELEPHASE II (now there are 4 gametes with 23 c’somes)
describe processes of crossing over and recombination in regard to genetic variation
- crossing over - exchange of sections of DNA between homologous chromosome pairs during prophase of meiosis I
- part of process of unique chromosome production call recombination
compare and contrast process of spermatogenesis and oogenesis
SIMILARITIES:
- result in haploid gametes that are genetically variable
- occur in gonads
- processes controlled by hormones
DIFFERENCES:
LOCATION (spermatogenesis –> all completed in testes; oogenesis –> begins in ovaries, completed in fallopian tube)
COMPLETION (s –> division completed regardless of fertilisation; o –> meiosis II only completed if fertilisation occurs)
NO. CELLS (s –> all 4 daughter cells become sperm; o –> only 1 daughter cell becomes an egg, others become polar bodies)
TIMING (s –> continuous process from onset of puberty; o –> begins during foetal development, pauses until puberty, stops at menopause)
SPECIALISATION (s –> smaller, motile, tail, high mitochondrial numbers; o –> larger, non-motile, nutrient storage levels are high)
Define the terms ‘gene’ and ‘genome’,
GENE - section of DNA that codes for proteins; inherited from parent to offspring
GENOME - complete set of all gene-containing chromosomes an individual carries in cells
Describe coding and noncoding genes
CODING GENES:
- code contained in nucleotide triplet –> codon
- each codon corresponds to an amino acid
NONCODING GENES:
- production of functional RNA
- regulating gene expression (control structural genes)
- centromeres (points of attachment of chromatids)
- telomeres (endcaps of each c’some)
- introns (non-coding DNA within split gene)
- many functions yet to be determined
Explain process of transcription
- process that occurs in nucleus of eukaryotic cells
- allows single-stranded mRNA molecules to be produced from double-stranded DNA
INITIATION:
- RNA polymerase unzips DNA double helix by breaking hydrogen bonds between bases
- this exposes based, allowing them to bind with free gloating nucleotides during elongation
ELONGATION:
- RNA polymerase moves along exposed DNA strand, using it as a template to build mRNA strand from free-floating nucleotides
- synthesis of mRNA follows same base pairing as DNA, except A now pairs with U
TERMINATION:
- stop codon signals RNA polymerase to cease transcription and terminate mRNA molecule
Explain the process of translation
- ribosomes build polypeptide chain from amino acids by translating mRNA codons
INITIATION:
- ribosomal subunit attaches itself and moves along mRNA strand until it recognises a start codon
- free-floating transfer RNA (tRNA) molecule with corresponding anticodon attaches to mRNA start codon –> now ready to begin translating
ELONGATION:
- as ribosome progresses along mRNA strand, it reads codons and matches them with anticodon of nearby tRNA molecules
- as each tRNA anticodon binds with corresponding mRNA codon, it release its amino acid, which joins growing polypeptide chain through condensation polymerisation reaction
TERMINATION:
- ribosome reads stop codon and releases polypeptide chain into cytoplasm
- free-floating polypeptide chain them moves to endoplasmic reticulum or Golgi apparatus where it will undergo further processing to become a functional protein
Describe factors that regulate gene expression
- REGULATION THROUGH PRODUCTS OF OTHER GENES
- regulatory genes –> control expression of other genes
- eg. repressors that stop production of protein coded on another gene - REGULATION DURING TRANSCRIPTION
- histone acetylation/methylation:- if DNA is loosely bound around histones (acetylation), DNA is more easily copied
- if DNA is more tightly bound around histones (methylation), it is more difficult to copy
- these processes act like a dial
- DNA acetylation/methylation:
- chemical tag (methylation) added to DNA to “switch off” gene
- alternatively, tag is removed (acetylation) to “switch on” gene
- REGULATION DURING TRANSLATION
- mRNA binding proteins –> some proteins can bind to mRNA blocking translation process
- micro RNA –> short fragments of RNA can bind with mRNA and interfere with translation - REGULATION VIA ENVIRONMENTAL EXPOSURE
- epigenome incorporates environmental exposures outside the cell
- factors such as diet, diurnal and seasonal changes, exposure to meds, disease and chemicals can influence expression/repression of genes
Describe transcription factors and Hox genes
- transcription factors determine when and where genes are expressed
Hox genes control position of body structures along head to tail axis
Explain gene mutations and how they can occur
- mutation is a change in DNA sequence that results in different version of a gene (i.e. allele)
- can be change of single nucleotide base pair, or changes to entire genes or chromosomes
POINT MUTATIONS:
- change to single nucleotide base
- can change amino acid added to polypeptide chain
- substitution, nonsense mutation, insertion frameshift, or deletion frameshift
NON-DISJUNCTION:
- occurs when spindle fibres fail to separate chromatids during anaphase (can occur in meiosis I or II, or mitosis)
- daughter cells have abnormal no. chromosomes –> referred to as ANEUPLOIDY
DAMAGE BY MUTOGENS:
- mutations can be caused by mutagens (eg. UV radiation, ionising radiation, heat, or chemicals)
SOMATIC MUTATIONS:
- mutations withing somatic cells, so will only affect individual because DNA is not passed to offspring
INHERITED MUTATIONS:
- mutations in germ line cells (sperm and egg), which are passed on to offspring
explain karyotypes
- karyotype is an image of an individual organism’s complete set of chromosomes in their homologous pairs
- average human has 23 c’somes –> 22 somatic and XX (female) or XY (male)
Explain alleles, genotypes, and phenotypes (in regards to inheritance)
ALLELES:
- different versions of genes
- can be dominant or recessive
- in diploid cells, there are 2 of each chromosome, so the dominant will be expressed
GENOTYPES = allele organism carries for a particular trait
PHENOTYPES = describes the trait expressed
describe frequency histograms (in regards to inheritance and phenotypes)
- provide visual representation of selected trait frequencies in population/species
- commonly produced with discrete traits such as allele presence, genotype, or phenotype on x-axis, and frequency on y-axis
describe punnett squares
- tool used to predict all possible genotypes and phenotypes of offspring of known parents
- it is possible to predict probability of genotypes and phenotypes when allele dominance is known
DRAWN WITH FOLLOWING FEATURES:
- alleles of one parent on top, and alleles of other parent on side
- corresponding combinations of alleles written in spaces aligning with parents’ alleles
- percent geno/pheno determined
describe autosomal dominance
- dominance exhibited by any chromosome other than a sex chromosome causing traits or conditions to be expressed in pheno. of the organism
describe sex-linked inheritance
- X and Y carry genes for traits other than biological sex, and have different pattern of inheritance from those of autosomal genes
EXAMPLES OF DIFFERENT TYPES OF SEX-LINKED INHERITANCE:
- X-LINKED RECESSIVE - since males have 1 copy of X c’some, X-linked recessive are more likely to appear in males than females
- X-LINKED DOMINANT - higher prob. of appearing in general pop.
- Y-LINKED INHERITANCE - Y c’some is smaller (less genes), so Y-linked inheritance is rarely seen
- SEX-LIMITED INHERITANCE - some traits only appear in one sex –> if genotype that affects male trait is carried by female, it will not be expressed since male characteristic is absent in females
explain phenotypic characteristics of multiple alleles and explain polygenic inheritance
MULTIPLE ALLELES
- when more than 2 alleles control a pheno.
- eg. blood type –> 3 alleles, 4 possible pheno. (A, B, AB, O) –> A and B are dominant over O, so both A and B can be expressed if both present
POLYGENIC INHERITANCE:
- some pheno. traits have many variations between 2 extremes (eg. height or skin colour)
- traits controlled by multiple genes
- effect of dominance and segregation still apply, and combined contributions result in wide range of phenotypic possibilities
isolation, insertion, joining, amplification
describe process of making recombinant DNA (4 steps)
RECOMBINANT DNA:
- DNA strand containing genetic sequence artificially inserted in laboratory
- goal is to move target gene from donor organism into vector organism
ISOLATION
- target gene is identified in donor organism and isolated using restriction enzyme that cuts DNA at specific base sequence called recognition site
- isolated DNA fragment left with sticky end, allowing it to be joined to corresponding exposed DNA sequence in plasmid of vector organism
INSERTION:
- plasmid (circular molecule of DNA found in cytoplasm of bacteria) of vector organism is cut with same restriction enzyme used on target gene
- target gene is added to plasmid to allow for joining to occur at sticky ends of both molecules
JOINING:
- sticky ends of target gene join according to matching base pairs and enzyme called DNA ligase glues segments of DNA together to form complete and continuous DNA segment
AMPLIFICATION:
- bacteria containing recombinant plasmid are allowed to replicate, producing millions of copies of target gene to allow for mass production of desired protein
recognise applications of DNA sequencing to map genomes and DNA profiling
- DNA sequencing allows DNA and protein sequences to be analysed and interpreted
- this tech. allows detailed info about genes, and how they work
- genome mapping involves determining locus of a gene on a c’some and the relative location of a gene in relation to others
- mapping this info assists scientists when working on treatments for genetic diseases
explain polymerase chain reaction (PCR)
- technique for amplifying small samples of DNA
DENATURATION:
- temp. of sample raised to 95°C to break hydrogen bonds between DNA nucleotides, creating 2 single-strands
ANNEALING:
- temp. lowered to below 60°C, allowing primers to bind (anneal) to start of DNA sequence
EXTENTION:
- temp. raised to 72°C, allowing Taq polymerase to attach to primers and add free-floating nucleotides as it moves along exposed sequence, creating double stranded DNA
- repeat for many cycles, exponential growth, millions of copies made
explain gel electrophoresis
- procedure to separate fragments of DNA according to size, allowing samples from different indiv. to be compared
- samples placed in gel that has electric current
- DNA has -ve charge, so moves towards +ve end
- smaller molecules move through gel further than larger
- used to compare samples from crime scenes to suspects, or sample from child to possible fathers to find paternity
