Science Subtest Iii: Genetics

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the process of copying DNA to make 2 new DNA molecules

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DNA replication

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DNA replication is completed just before

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cell division

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Name the four steps of DNA replication

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1. open helix (helicase)
2. add new DNA nucleotides
A=T, C=G (DNA Polymerase)
3. Open up more helix, restart lagging strand
4. Join together lagging strands (ligase) and twist up 2 new helices

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Explain DNA replication

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DNA copies itself in a process called DNA replication. First, an enzyme called helicase "unzips" the two strands in the double helix. Then DNA polymerase adds new nucleotides to the new strands. Finally, ligase rejoins the strands and they twist into a helix.

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function of proteins

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structure and support (hair)
storage of amino acids (casein in milk)
coordination of body activities (insulin)
transport of substances (hemoglobin)
signal transduction (membrane receptor proteins)
contraction (muscles, flagella)
body defense (antibodies)
enzymes (speed up chemical reactions)

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all ______ are made of combinations of several of the 20 amino acids

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proteins

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the ______ group varies and defines the amino acid

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radical

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peptide bond

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bond formed between between 2 amino acids

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Explain the analogy drawn between the 20 amino acids and the alphabet

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we can form millions of words using an alphabet of only 26 letters. Similarly, organisms create many different proteins using the twenty amino acids. This results in the formation of many different proteins

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for proteins, ________ defines the function

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structure

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primary, secondary, tertiary, quaternary are

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the four levels of proteins

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proteins unique sequence of amino acids; a slight change in this structure can affect a proteins conformation and its ability to function

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primary structure

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the coils and folds of polypeptide chains; either in the form of an alpha helix or pleated sheet

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secondary structure

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what is the difference between a pleated sheet and an alpha helix

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pleated sheet: the polypeptide chain folding back and forth
alpha helix: a coil held together by hydrogen bonds

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formed by bonding between the side chains of the amino acids

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tertiary structure

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the overall structure of the protein from the aggregation of two or more polypeptide chains. Example: hemoglobin, consists of two kinds of polypeptide chains

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quaternary structure

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nucleic acids consist of

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DNA and RNA

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______ contain the code for the amino acid sequence of proteins and the instructions for replicating

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nucleic acids

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name the 5 bases of nucleic acids

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adenine, thymine, cytocine, guanine, uracil

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_______ is found only in RNA and replaces thymine

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uracil

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the _____ sequence is the code or the instructions

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base

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DNA replicates semiconservatively. What does this mean

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the 2 original strands are conserved and serve as a template for the new strand

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what is the role of the enzyme helicase in DNA replication

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helicase unwinds the DNA

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proteins are synthesized through the processes of

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transcription and translation

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Three major classes of RNA are needed to carry out transcription and translation including:

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messenger RNA (mRNA)
ribosomal RNA (rRNA)
transfer RNA (tRNA)

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what is the function of mRNA, tRNA, and rRNA

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messenger RNA (mRNA): contains information for translation
ribosomal RNA (rRNA): stuctural component of the ribosome
transfer RNA (tRNA): carries amino acids to the ribosome for protein synthesis

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During transcription the

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DNA molecule is copied into an RNA molecule (mRNA)

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The 3 steps of transcription include:

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1. Initiation
2. Elongation
3. Termination

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initiation begins at

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the promoter of the DNA molecule

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a specific region of DNA that directs the RNA polymerase to bind the DNA is

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the promoter

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the doublet stranded DNA opens up and RNA polymerase begins transcription by

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pairing ribonucleotides to the deoxyribonucleotides to get complementary mRNA segments

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what does a complementary mRNA segment look like

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A ------> U
G ------> C

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The synthesis on the mRNA strand in the 5' ----> 3' direction is

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elongation

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describe elongation

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the new mRNA rapidly seperates from the DNA template and the complimentary DNA strands pair together

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termination of transcription occurs at the

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end of the gene

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in ________, mRNA goes through postranscriptional processing before going on to translation

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eukaryotes

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the three basic steps of processing are

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5' capping
3' polyadenylation
intron removal

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_______ is the process in which the mRNA sequence becomes a polypeptide

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translation

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the _____ sequence determines the _______ sequence of a protein by following a pattern called the genetic code

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mRNA
amino acid

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the genetic code consists of

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64 triplet nucleotide combinations called codons

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_____ codons are termination codons

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3

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the remaining 61 code for

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amino acids

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the site of translation

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ribosomes

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translation occurs in the three steps including:

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initiation, elongation, termination

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________ occurs when the methylated tRNA binds to the ribosome form a complex

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initiation

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this complex then binds to the _____ of the mRNA

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5' cap

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what happens in elongation

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tRNAs carry the amino acid to the ribosome and place it in order according to the mRNA sequence

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tRNA is very specific, it only accepts one of the 20 amino acids that corresponds to the

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anticodon

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explain the codon sequence

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mRNA reads: A U G
anticodons are: U A C

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Termination occurs when

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the ribosome reaches any one of the three stop codons: UAA, UAG, UGA

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the physical structures found in every cell that carry the DNA of an organism and function in the transmission of hereditary information are

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chromosomes

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each chromosome contains a sequence of genes each with a

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specific locus

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a locus is

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the position a given gene occupies on chromosome

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each gene consists of a sequence of DNA that

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dictates a particular characteristic of an organism

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regions of DNA that do code for proteins and seperate the genes on a chromosome may function in the

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regulation of coding regions

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meiosis and fertilization promote variation through which three mechanisms

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independant assortment
crossing over
random fertilzation

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independant assortment takes place during which stage of meiosis

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metaphase I

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the orientation of the homologous pairs along the metaphase plate is random and independent of the other pairs of chromosomes in metaphase I. This results in an _________ of maternal and paternal chromosomes

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independent assortment

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a process called ______ prevents each chromosome in a gamete from being of only maternal or paternal origin

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crossing over

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crossing over occurs during which phase of meiosis

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prophase I

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nonsister chromatids cross and exchange corresponding segments during the mechanism ______

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crossing over

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_______ results in the combination of DNA from both parents, allowing for greater genetic variation in sexual life cycles

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crossing over

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each parent has about 8 millon possible chromosome combinations this allows for over 60 trillion _______ combinations = ________

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diploid
random fertilization

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the unit of inheritance are

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genes

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in humans, chromosomal ______ determines the sex of the individual

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crossing over
women give an X chromosome always
men either pass on an X or Y chromosome

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it is the pairing of _______ and _______ genes that determines the sex of the baby

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maternal
paternal

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parents pass on genes affecting ______ such as eye color, height, etc

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phenotype

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changes in either the total number of chromosomes or their shape and size are

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chromosomal aberrations

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chromosomal aberations may lead to

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abnormalities in the offspring

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an aberration on chromosome 21 causes

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down syndrome

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difference between genotype and phenotype

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genotype: the actual information on the genes
phenotype: how that information is expressed outwardly

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incomplete dominance

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when the F1 generation results in an appearence somewhere between the two parents

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codominance

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the genes may form new phenotypes

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example of codominance

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ABO blood grouping. A and B are of equal strength and O is recessive. Therefore, type A blood may have the genotypes of AA or AO, type B blood may have the genotypes of BB or BO, type AB blood has the genotype A and B and type O blood has two recessive O genes

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22 of the 23 pair of chromosomes, called autosomes, are the

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same in males and females

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Which pair differs from autosomes

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the sex chromosomes

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sex-linked traits

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specific genes located on the sex chromosomes that are responsible for specific actions

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Example of sex-linked traits

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hemophilia which is determined by a gene defect on an X chromosome

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traits or characteristics came in serveral forms known as

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alleles (pp) or (PP)

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the law of _______ states that only one of the two possible alleles from each parent is passed on to the offspring

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segregation

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having a pair of identical alleles. For example: PP and pp

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homozygous

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having two different alleles. For example: Pp

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heterozygous

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the organisms physical appearence

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phenotype

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the organisms genetic makeup. For example: PP and Pp _______ have the same phenotype (purple in color)

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genotype

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dominant allele

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one allele fully expressed in the organisms appearence

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recessive allele

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allele with no noticeable effect on appearence

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the law of _______ states that alleles assort independetly of each other

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independent assortment

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monohybrid cross

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one character

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dihybrid cross

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two characters

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How does random chromosome segregation explain the probability that a particular allele will be in a gamete

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the law of segregation states that only one of the two possible alleles from each parent is passed on to the offspring. If the two alleles differ, then one is fully expressed in the organisms appearence (dominant allele) and the other has no noticeable effect on appearence (recessive allele)

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the two alleles for each trait segregate into

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different gametes

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there is a ___/___ chance that each allele could be segregated into a particular gene

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50/50

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cellular specilization generally depends on changes in ______ rather than on different genes being present

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gene expression

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gene expression

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process of how a gene is used to affect an organisms traits

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cell types in a multicellular organism are different from one another because of the synthesis of

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RNA and protein molecules, this occurs without alteration to the sequence of DNA

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an organisms cells contain the same ______

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genome

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a promoter and operator in a cell are the

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on and off switch

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genes can be expressed or turned on and off

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for instance, we are born with certain genes that get turned on when we go through puberty (boobs, hair, etc.)

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because of the existence of dominant and recessive alleles, individuals may exist in a population as _______ without any outward signs of disease

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carriers

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example of how alleles that are lethal in a homozygous individual may be carried in a heterozygote and maintained in the gene pool

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Cystic Fibrosis (CF) - considered an autosomal recessive disease. If a child inherits BOTH recessive non-functioning genes it will be a homozygous recessive individual and the result will be CF

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Inheritable changes in DNA are called

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mutations

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mutations may be errors in replication or

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a spontaneous rearrangement of one or more segments by factors like radioactivity, drugs, or chemicals

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the severity of change is not as important as

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where the change occurs

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exons

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important coding areas

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introns

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noncoding areas

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usually the mutations on ____ cells are more dangerous

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sex

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types of mutations

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point
frame shift
silent
missense
loss-of-function

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mutuation involving a single nucleotide or a few adjacent nucleotides

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point mutation

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deletion and insertion mutations that shift the reading frame are

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frame shift mutations

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a _______ mutations makes no change in the amino acid sequence, therefore it does not alter the protein function

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silent

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a _______ mutation results in an alteration in the amino acid sequence

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missense

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a mutation that does not alter ______ will probably have little or no effect on the proteins function

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structure

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a mutation that does alter the structure of a protein and can severly affect protein activity is called a ______ mutation

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loss-of-function

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example of loss-of-function mutation

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cystic fibrosis and sickle-cell anemia

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examples of how genetic engineering (biotechnology) produces biomedical products

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the use of DNA probes and the polymerase chain reaction (PNR) has enabled scientists to identify and detect pathogens
diagnosis of genetic disease is now possible before onset of symptoms
insulin treatment: insulin produced in genetically engineered bacteria
advanced the techniques used to create vaccines

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gene therapy

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the introduction of a normal allele to the somatic cells to replace the defective allele

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example of how biotechnology benefitted agriculture

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dairy cows are given bovine growth hormone to increase milk production
strains of wheat, cotton, soybeans have been developed to resist herbicides used to control weeds which allows for successful growth of plant while destroying weeds

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crop plants are being engineered to

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resist infections and pests

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crop plants are now being modified to resist insect attacks which allows farmers to reduce

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the amount of pesticide used on plants

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_______ requires enzymes to cut DNA, a vector, and a host organism for the recombinant DNA

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genetic engineering

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a bacterial enzyme that cuts foreign DNA in specific locations

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restriction enzyme

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the restriction fragment that results can be inserted into a

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bacterial plasmid (vector)

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the ______ of restriction fragments into a plasmid results in a recombinant plasmid

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splicing

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this recombinant plasmid can be placed in a ______ cell, usually a bacterial cell for replication

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host

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the use of recombinant DNA provides a means to

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transplant genes among species - opens door for cloning specific genes of interest

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a ______ is a molecule complementary in sequence to the gene of interest

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gene

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another method for analyzing DNA is

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gel electrophoresis

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electrophoresis

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seperates DNA or protein by size or electrical charge. the DNA runs towards the positive charge and the DNA fragments seperate by size.

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polymerase chain reaction (PCR)

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is a technique in which a piece of DNA can be amplified into billions of copies. this process requires a primer to specify the segment to be copied, and an enzyme to amplify the DNA

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the goal of genetic engineering is

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to introduce new attributes that are deemed to be an improvement. Practical and medical uses to humans

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example of genetic engineering

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production of human insulin through modified bacteria

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cloning

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duplication of genetic information

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example of cloning in nature by chance

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creation of identical twins
asexual reproduction

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goal of human genome project

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to map and sequence the three billion nucleotides in the human genome and to identify all of the genes on it

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advances in the human genome project have led to a greater understanding of

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the functions of specific genes

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gene therapy is a short lived solution because

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after the insertion the target cells must remain functional and the cells containing the therapeutic DNA must be long lived and stable

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always the risk for inflammatory response in

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gene therapy

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asexual reproduction

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Asexual reproduction is a type of reproduction found mostly in prokaryotes. Asexual reproduction doesn’t require fertilization and only one parent cell is needed to reproduce. In achaea and bacteria, the type of cell division that is involved in asexual reproduction is known as binary fission

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sexual reproduction

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Meiosis is a type of cell division that produces gametes. In meiosis, cells undergo two divisions. The result of meiosis is the production of four haploid cells from a diploid cell with each haploid cell contains half of the number of chromosomes and half of the genetic materials of a diploid cell. Meiosis has many similar mechanisms to mitosis. The stages of meiosis include prophase I, metaphase I, anaphase I and telophase I followed by prophase II metaphase II, anaphase II and telophase II.