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S2 Science Exam

DNA and Meiosis

List the steps of mitosis in order Prophase Metaphase Anaphase Telophase
Describe prophase in mitosis: the chromosomes condense from long strands to rod-like structures
Describe metaphase in mitosis: the chromatids meet in a line at the equator of the cell. Nuclear membrane fully dissolves.
Describe anaphase in mitosis: chromatids separate into two different groups and move to opposite sides of cell
Describe telophase in mitosis: each group of chromosomes is enclosed by their own nuclear membrane. Chromosomes unwind, mitosis complete.
List the steps of meiosis in order: interphase Prophase 1 Metaphase 1 Anaphase 1 Telophase 1 Prophase 2 Metaphase 2 Anaphase 2 Telophase 2 Cytokenesis
Describe interphase in meiosis: each chromosome makes a copy of itself, forming two halves called chromatids.
Describe prophase 1 in meiosis: the chromosomes condense into rod-like structures. Homologous chromosomes cross over and exchange DNA
Describe metaphase 1 in meiosis: homologous chromosome pairs line up at the equator of the cell. Spindle fibers attach to chromosomes.
Describe anaphase 1 in meiosis: Homologous chromosomes separate and movie to opposite sides of the cell.
Describe telophase 1 in meiosis: the nuclear membrane reforms around each group of chromosomes and the cell pinches in two.
Describe prophase 2 in meiosis: Each of the two cells now has one chromosome from each homologous chromosome pair.
Describe metaphase 2 in meiosis: the chromosomes in each cell line up at the equator of the cell. Spindle fibers attach themselves to the chromosomes.
Describe anaphase 2 in meiosis: Chromatids pull apart and move to opposite sides of each cell
Describe telophase 2 in meiosis: each of the groups of chromosomes is enclosed by its own nuclear membrane.
Describe cytokenesis in meiosis: both cells pinch into two, leaving 4 sex cells each with half the number of chromosomes that were in the original cell
What is a chromosome? A structure in the nucleus containing DNA
What are sex chromosomes? Sex chromosomes carry the genes that determine sex.
What sex chromosomes do females have? Two x chromosomes
What sex chromosomes do males have? One x and one y chromosome
Describe how chromosomes determine sex Each egg cell will have one x chromosome. Each sperm cell will have either an x or y chromosome. So when the egg and sperm meet, the offspring will either be female (XX) or male (XY)
Why do sex linked disorders happen in males more often? The genes for these disorders are carried on the x chromosome and are recessive. The females have a backup gene copy (XX), but males don’t (XY)
What is the main difference between mitosis and meiosis? - meiosis produces 4 sex cells, each have half # of chromosomes that were in original cell - mitosis produces 2 normal cells, each have same # of chromosomes that were original cell
What is another difference between meiosis and mitosis? Only in meiosis: homologous chromosomes cross over and exchange DNA in p 1
List three important events that lead to understanding the DNA structure. Chargaff’s contributions Franklin's contributions Watson and Crick’s contributions
Who was Edwin Chargraff? What did he contribute to DNA ? A biochemist discovered Chargraff's rules: states that amount of a always = t and amount g always = c.
Who was Rosalind Franklin? What did she contribute to DNA ? British chemist used xray diffraction to make images of DNA found that DNA has spiral shape
Who were Watson and Crick? What did they contribute to DNA ? James Watson and Francis Crick = scientists Built twisted ladder model that later explained DNA replications and functions
What are the subunits of DNA called? What do they consist of? Nucleotide consists of nitrogen base, sugar, phosphate
The 4 nitrogen bases are ... What pairs with what? Adenine, Thymine, Guanine, Cytosine A--> T G-->C
Each nitrogen base has a different ____. shape
What are purines? Adenine and Guanine
What are pyrimidines? Thymine and Cytosine
What is the shape of DNA called? Double helix.
The alternating _____ and ____ make up the sides of the ladder sugars and phosphates
The pairs of __________ make up the rungs of the ladder. Nitrogen Bases
Why is it that a is paired with t and g with c? The width of the combined base pairs matches the width of the ladder
What is a hydrogen bond? how many between g and c? between a and t? the attraction that holds together two nitrogen bases 3 between g and c, 2 between a and t
Define DNA replication. Why is it important? DNA replication is the process in which it copies itself. Important so that each cell contains identical genes.
Explain Steps of DNA replication: 1)Double helix unwinds out of twisted form 2)Unwound DNA unzips itself where bases meet 3)Free.f. complementary nucleotides attach to exposed bases, creates 2 strands ofDNA 4)Each completed strand rewinds into double helix, leaves 2 copies of original
If adenine makes up 30 % of a DNA strand, what percent is cytosine? A = 30 --> t = 30 C + G = 100-60 = 40 C = 20%
Define DNA transcription Transcription is the process of making mRNA from DNA
Explain the steps of DNA transcription 1) DNA polymerose (molecular machines) unwinds a small section of the DNA 2) Free-floating nucleotides attach to one unzipped part of the DNA, leaving the other part untouched. Same base pairings except Adenine (A) pairs with Uracil (U).
(Steps of DNA transcription continued) 3) The half with the original DNA leaves the strand with the uracil, and rejoins with the untouched part of original DNA 4) The uracil strand is left on its own, and it is called mRNA
What is mRNA? A single strand similar to a DNA strand (Except for u instead of t) that is used to build proteins
Define DNA translation. Translation is the process in which mRNA is used to make proteins
Explain the steps of DNA translation. 1) mRNA leaves the nucleus through the nuclear pores, enters the cytoplasm, is fed through a ribosome 2) tRNA pairs up with the 3 letter codons of the mRNA (group of 3 nitrogen bases)
(steps of DNA translation ctd) 3)The tRNA brings a specific amino acid with it to the ribosome and then detaches itself from the codons, leaves the ribosome. 4 Other tRNA do same thing, and a chain of amino acids forms. 5) These amino acids will combine to form the needed proteins
List three types of mutations. Point Missense/Substitution Point Nonsense/substitution stop Frameshift/deletion/insertion
What is happens in point nonsense? What is the result? - When a different nitrogen base is substituted in the sequence, and the different base creates a stop codon - the protein does not form properly → disorders
What is happens in point missense? What is the result? - When a different nitrogen base is substituted in the sequence - could make diff amino acid making protein nonfunctional - could make same amino acid, no change
What is happens in frameshift? What is the result? -When a nitrogen base is added or taken away from the sequence - causes very different amino acids to form --> severe genetic disorders
Who was Walter Sutton? What did he discover? scientist who discovered genes are located on chromosomes
Created by: mhaq.16