Cell continuity topic 6 Flashcards
what is chromatin? and how is it formed?
-the DNA molecule in a human cell that is cut short and wrapped up with histone proteins which forms a complex called chromatin
when will chromatin unwind?
-when genes need to be transcribed
when does DNA replication take place, why does it take place and how does it occur?
-before cell division DNA is replicated and more histone proteins are synthesized so temporarily there is twice the normal amount of chromatin
what is the structure of a chromosome?
-x shaped because it contains two replicated copies of DNA
-each arm of the chromosomes are called chromatin which are joined at the centromere
what are the three stages of interphase?
-gap 1
-synthesis
-gap 2
-gap 0
what happens during G1?
-just after mitosis
-new cell produces organelles in cytoplasm which increases the size of the cell
what happens during the s phase?
-chromosomes are replicated which allows the chromosomes can be passed on to the new cell
-before DNA synthesis chromosomes replicate and produce an x like structure with two chromatids
-histones form
what happens during G2?
-period before mitosis and the cell accumulates stores of energy to prepare for cell division
-spindle fibers are synthesized
-chromosomes are checked for error and repaired if necessary
what does mitosis used for, where does it occur and how many stages does it have?
-used for growth and asexual reproduction
-occurs in all cells except gametes
-has 5 stages prophase, metaphase, anaphase, telophase, cytokinesis
what happens during prophase during mitosis?
-chromosomes condense
-each chromosome consists of two identical sister chromatids connected by a centromere
-centrioles move to opposite poles
-nucleolus disappears and nuclear membrane breakdown
what happens during metaphase during mitosis?
-spindle fibers connect centrioles to chromosomes
-chromosomes align along equator of cell and attaches to a spindle fiber by its centromere
what happens during anaphase in mitosis?
-centromeres split allowing chromatids to split
-chromatids move towards poles pulled by motor proteins walking along microtubules
-mitochondria provide energy for this
what happens during telophase in mitosis?
-spindle fibers disperse
-nuclear membrane form around each set of chromatids
-nucleoli form
what happens during cytokinesis in animal cells during mitosis?
-ring of actin filaments form round the equator which tightens to form a cleavage furrow which splits cell in two
what happens during cytokinesis in plant cells during mitosis?
-vesicles line up and fuse at equator to form two membrane called the cell plate
-new cell wall is laid down between membranes which fuses with existing cell wall
what is cancer?
-uncontrolled cell division
how does cancer occur?
-each cell cycle has a checkpoint and during cancer these checkpoints dont work and so dont enter gap 0 which causes uncontrolled cell growth
what is a way that some cancers can be treated?
-chemotherapy which invovles drugs that inhibit stages in the cell cycle
what are the two types of drugs used in chemotherapy and what happens during them?
-vincristine= stops microtubules forming spindle fibers and so chromatids cannot be pulled apart during anaphase
-fluorouracil= is an antimetabolite which prevents DNA synthesis at s phase
how do anti cancer drugs affect normal cells?
-they affect normal cells too which results in unpleasant side effects
what is meant by homologous pairs?
-chromosomes that come in pairs
-homologous pairs are a result of sexual reproduction and the homologous pairs are the maternal and paternal versions of the same chromosomes, they have the same sequence of genes
how many pairs of chromosomes are different in males and females?
-one pair which are the sex chromosomes meaning they are non homologous
-females have xx males have xy
where does meiosis occur and what does it produce?
-occurs in ovaries and testes and produces gametes with half the number of chromosomes
-meiosis results in 4 haploid genetically different daughter cells
what does diploid and haploid mean?
-diploid means the full number of cells which is 46 (2n)
-haploid means half the number of cells which is 23 (n)
how does mitosis and meiosis differ?
-meiosis results in haploid numbers because it allows the chromosome number to remain constant from generation to generation. Haploid cells have one copy of each chromosome and diploid have homologous pairs
-chromosomes are rearranged during meiosis which results in genetic variation
how many stages occur during meiosis and what are each of their steps?
-two stages
-first stage has 4 phases and results in the exchange of genetic material
-second stage has 5 phases
what happens during prophase 1 in meiosis?
-chromosomes condense
-homologous chromosomes join to form a bivalent
-chromatids cross over to exchange genetic material known as chiasmata formation
what happens during metaphase 1 during meiosis?
-bivalents line up at equator
-nuclear membrane disappears
what happens during anaphase 1 during meiosis?
-chromosomes separate and are pulled apart
-not the chromatids as the centromere doesnt split
what happens during telophase 1 during meiosis?
-nuclear membrane reforms
-cell divides into two
-each cell has 2 chromosomes not 4 chromatids because the chromatids are still joined by the centromere
what happens during prophase 2 during meiosis?
-centrioles move to poles
what happens during metaphase 2 during meiosis?
-nuclear membrane disappears
-chromosomes line up on equator
what happens during anaphase 2 during meiosis?
-centromeres split
-chromatids separate and pulled to opposite ends of cell
-once they are separated each chromatid is known as a chromosome
what happens during telophase 2 during meiosis?
-nuclear membrane reforms
what happens during cytokinesis during meiosis?
-cell membrane forms which divides the cells into 4 daughter cells
-there four haploid cells contain two chromosomes
what are the 2 stages of sexual reproduction and what happens?
-meiosis happens first which is the type of cell division that results in haploid gametes
-fertilization the occurs which is the fusion of two gametes forming a diploid zygote
what are 5 differences between mitosis and meiosis?
-mitosis produces two diploid daughter cells and meiosis results in 4 haploid cells
-mitosis is one cell division and meiosis is 2
-in mitosis chromosomes do not pair up and in meiosis they do pair up and exchange genetic material
-mitosis is asexual reproduction which results in clones and meiosis is sexual reproduction which results in genetic variation
-mitosis occurs in all cells except testes and ovaries and meiosis occurs only in testes and ovaries
what are the three ways that meiosis results in genetic variation?
-independent assortment
-random fertilization
-crossing over in meiosis
how does independent assortment result in genetic variation?
-happens at metaphase 1 in meiosis when bivalents line up at equator
-they can line up in any order, the maternal and paternal versions of the different chromosomes can be mixed up in the final gametes
how does random fertilization result in genetic variation?
-takes place when two gametes fuse to form a zygote
-each gamete has a unique combination of genes and any of the numerous male gametes can fertilize any of the numerous female gametes
how does crossing over result in genetic variation?
-at prophase 1 homologous chromosomes come together to form bivalents
-chiasmata formation results in genes from one chromosome are exchanges with the corresponding genes of the other chromosome
what are chiasmata?
-the point where chromosomes actually cross over, they involve large multi enzyme that cut and join DNA
-equal amounts of chromosomes cross over so they stay the same length
-chiasmata therefore results in different allele combinations
