Molecular and Human Genetics

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Molecular and HumanMolecular and Human Genetics

AP Biology Rapid Learning Series

Rapid Learning Centerwww.RapidLearningCenter.com/© Rapid Learning Inc. All rights reserved.

AP Biology Rapid Learning SeriesWayne Huang, PhD

Andrew Graham, PhDElizabeth James, PhD

Casandra Rauser, PhD Jessica Habashi, PhD

Sara Olson, PhDJessica Barnes, PhD



Learning Objectives

By completing this tutorial, you will learn about:

Structure and Function of DNA

Structure of RNA

Protein Synthesis

Molecular Genetics: Northern Blot, Southern Blot, and DNA

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, ,Cloning

Human Genetics

Concept Map

Genetics Molecular Genetics

Human Genetics

mRNA

Structure of RNA

Structure andFunction of DNA

rRNA

tRNA

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rRNA

ProteinTranslation

Karyotype Sex-linkedTraits

Functional ProteinSynthesis



Structure and Function of DNA

Molecular Genetics, DNA

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Molecular Genetics

Molecular genetics is a division of biology that is involved in the study of gene structure and function.

The study of gene structure has lead to a further understanding of certain disease processes, as well p ,as potential gene therapies.

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Cell NucleusThe cell nucleus is usually near the center of the cell; it contains the majority of the genetic material in a cell. Within the nucleus, the DNA is compacted and organized into chromosomes. Also within the nucleus is the nucleolus. The nucleolus has no true membrane surrounding it, and this is where ribosomes are producedthis is where ribosomes are produced.

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The cell nucleus is surrounded by a nuclear envelope, which contains pores to limit flow in and out of the nucleus. The pores allow small water-soluble molecules to diffuse into the nucleus but prevent large molecules, such as proteins, from randomly entering the cell. The outside of the nuclear membrane is continuous with the endoplasmic reticulum and the attached ribosomes.

Question: Challenge

Define, in general, what the nuclear envelope is.

The cell nucleus is usually near the center of the cell; it contains the majority of the genetic material in a cell. The cell nucleus is surrounded by a nuclear envelope, which

t i t li it fl i d t f th

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contains pores to limit flow in and out of the nucleus. The pores allow small water-soluble molecules to diffuse into the nucleus but prevent large molecules, such as proteins, from randomly entering the cell.



Nucleic Acids: DNA

Structurally DNA is made up of 2

Deoxyribonucleic acid (DNA) is the blueprint of life; it is present in almost every cell in the body. A copy from a male donor and a copy from a female donor, through fertilization, can create a human being.

Structurally, DNA is made up of 2 polymers of nucleotide in a complementary-based pair double helix. These anti-parallel strands run in opposite direction from one another and are held together through hydrogen bonds.

The structure of the double helix provides

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The structure of the double helix provides a major groove in which transcription factors can bind and impact gene expression. The four different DNA nucleotides follow a strict base pairing arrangement: Guanine – Cytosine (3 hydrogen bonds) and Adenine – Thymine (2 hydrogen bonds).

The genetic code dictates nucleic acid structure and function. The formation of the end-product amino acids and proteins is controlled by the genetic code set of rules. Within the code are codons, which are a nucleic acid sequence that specifies the formation of an amino acid.

Genetic Code

The genetic code allows for more than one codon to specify an amino acid. However, there is no

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ambiguity, as each codon specifies only one amino acid, depending on the reading frame or the context each codon is read in.



Semi-Conservative DNA Replication

DNA replication must take place in order for a cell to divide during mitosis.During DNA replication, the parental DNA is separated and each parent strand acts as a template for the formation of a new complementary strand. This is known as semi-conservative DNA replication. Each daughter cell

i d f h l ll DNA l i h i i lreceives one strand from the parental cell DNA, along with its one entirely new strand.

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Question: Challenge

Define, in general, what the genetic code is.

The genetic code dictates nucleic acid structure and function. The formation of the end-product amino acids and proteins is

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controlled by the genetic code set of rules. Within the code are codons, which are a nucleic acid sequence that specifies the formation of an amino acid.



RNA and Protein Synthesis

Structure of RNA, Protein Synthesis

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y

Ribonucleic acid (RNA) is usually single-stranded. It is made from a DNA blueprint. RNA translates the message from the DNA to produce

Nucleic Acids: RNA

translates the message from the DNA to produce the correct protein. The different types of RNA include:

(1) Messenger RNA (mRNA) – binds to ribosomes and provides the template for protein translation,(2) Transfer RNA (tRNA) – transfers a specific amino acid to the growing polypeptide protein at

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g g p yp p pthe site of translation, (3) Ribosomal RNA (rRNA )– the central component of the ribosome. It decodes messenger RNA and provides the actual binding site for the incoming tRNA.



Genes drive protein synthesis in the following manner: DNA is transcribed into RNA, and then RNA is translated into proteins. RNA is

d d b k

RNA Transcription

produced by an enzyme known as RNA Polymerase.

RNA polymerase transcribes a complementary base-paired RNA strand. During the base pairing, Uracil is substituted in the growing RNA strand for Thymine. The RNA strand produced by this process is known as messenger RNA

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this process is known as messenger RNA (mRNA). The process involves initiation, elongation of the transcript, and termination; it takes place in 5ʹ to 3ʹ direction. Only 1 DNA strand (template strand) is transcribed and, due to the complementary base pairing, the original instructions of the DNA are carried out.

There are three types of RNA: (1) Ribosomal RNA (rRNA) – ribosomal RNA is the central part of the ribosome, along with its associated proteins. rRNA decodes messenger RNA into the individual amino acids

Types of RNA

individual amino acids.

(2) Transfer RNA (tRNA) – transfer RNA contains an anti-codon region, which interacts with the appropriate codon on messenger RNA to ensure the proper amino acid is added to the growing protein. Transfer RNA has a single amino acid, which transfers to the growing

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g gprotein.

3) Messenger RNA (mRNA) – messenger RNA is the blueprint necessary for protein production. It binds to the ribosome and provides the codon, which is matched with the anti-codon of tRNA. This ensures the protein is assembled in strict accordance with the DNA template.



Question: Challenge

What are the 3 types of RNA?

(1) Messenger RNA (mRNA) – binds to ribosomes and provides the template for protein translation, (2) Transfer RNA (tRNA) –transfers a specific amino acid to the growing polypeptide protein at the site of

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g g p yp p ptranslation, (3) Ribosomal RNA (rRNA ) – the central component of the ribosome. It decodes messenger RNA and provides the actual binding site for the incoming tRNA.

Protein translation is the process whereby amino acids are assembled into a polypeptide chain or protein, based on the DNA code. The process involves the following steps:

Protein Translation

(1) Initiation – Once the ribosome is assembled, initiator tRNA, carrying methionine, binds to the start site on the mRNA.

(2) Elongation – After the initiator tRNA is bound to the P site the next tRNA is able to bind to the

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to the P site, the next tRNA is able to bind to the A site. Amino acids are added to the growing polypeptide chain by forming a peptide bond with the previous amino acid. Next, the mRNA is shifted by one codon, freeing up the A site to receive the next amino acid.

(3) Termination – Translation stops when one of three termination codons moves into the A site on the mRNA. Release factors trigger the release of the new protein.



Molecular Genetic Techniques

Cell Culture for Nucleic Acid Samples, Northern

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pBlot and Southern Blot

Tissue Cell Culture

Tissue culture is the process of growing cells and established cell lines in a controlled environment. Cells are grown in specific media, containing the necessary nutrient supplements and additives, such as hormones and growth factors.hormones and growth factors.

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Cells are grown in flasks, coated plates with individual wells, or in petri dishes. Most cells can be maintained in log phase growth by replacing the growth media when needed and storing the cells in humidified incubators at 37°C – to simulate body temperature.



Nucleic Acid Extraction

After cells are harvested by enzymatic digestion, they are prepared fornucleic acid extraction. First, the cells are broken or lysed, and then detergents and proteases are used to remove membrane lipids and unwanted proteins For extracting DNA graded alcohol solutions areunwanted proteins. For extracting DNA, graded alcohol solutions are used to precipitate the DNA out of solution. To detect DNA, light absorption spectroscopy can be used.

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Extracting RNA from cells requires the deactivation of ribonuclease enzymes, which would degrade the RNA sample. Usually, this takes place in the lysis buffer when the RNA extraction begins.

RNA Extraction: Northern BlotThe Northern Blot technique allows the experimenter to detect and study the RNA from cells. In general, total RNA is extracted from cellsRNA is extracted from cells, and then mRNA can be isolated to study gene expression.

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Once the RNA sample is extracted from the cells or tissue, it must be separated to probe for the RNA of interest. RNA can be separated using gel electrophoresis. Gel electrophoresis involves applying a current to a gel matrix containing the RNA sample. RNA samples move through the gel and separate into bands based on their charge to mass ratio. After separation, they can be transferred to a blot membrane and probed for the RNA of interest using a specifically labeled probe.



DNA Extraction: Southern BlotA Southern Blot is a technique to study the presence and levels of DNA sequences in cells under certain conditions. Similar to Northern blots, after the DNA is extracted from the cells, it is usually separated using gel electrophoresis.

Aft i ifi b t

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After using a specific probe to identify the DNA of interest, the results appear as bands. The bands are a result of autoradiography or other detection methods.

Gene CloningGene cloning can be used to create many copies of a defined DNA sequence. The sequence of DNA or gene can then be used to test the effect of over-expression or deletion of that gene from the genetic material of cells.

First, the DNA sequence of interest must be isolated. Next, the sequence is typically ligated into a plasmid, which then is used to transform the

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target cell or bacteria for gene production.



Question: Challenge

Define, in general, the method used to extract and investigate the DNA in cells.g

A Southern Blot is a technique to study the presence and levels of DNA sequences in cells under certain conditions. Similar to Northern blots, after the DNA is extracted from the cells it is usually separated using

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from the cells, it is usually separated using gel electrophoresis. After using a specific probe to identify the DNA of interest, the results appear as bands. The bands are a result of autoradiography or other detection methods.

Human Genetics

Karyotype, Population Genetics, and Genetic

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y yp pCounseling



KaryotypeCytogenetics involves the study of chromosomal abnormalities and deficiencies. As part of these studies, a karyotype is prepared. A karyotype is a visual pattern of the chromosomes within cells. By using stains and probes, whole chromosomes, short and long arms, and even small regions on chromosomes can be visualizedon chromosomes can be visualized.

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Normally, there are 22 pairs of autosomes and 1 pair of sex chromosomes, for a total of 46. Karyotypes can reveal the sex of the individual, as well as more finite details of the health. An example would be Down Syndrome, which is evidenced by 3 copies of all or part of chromosome 21.

Sex-Linked Traits: X-LinkedFor example: A gene (e.g. hemophilia) is recessive and located on the X chromosome; this is the inheritance pattern for that gene.

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X-linked means the gene of a particular trait resides on the X chromosome.



Y-linked traits appear only in males and are only passed from father to son.

Males contribute either an X or Y chromosome during fertilization. If an X chromosome is contributed, the genotype will be XX female; if a Y is contributed, the genotype will

Y-Linked Traits

Y-linked genes reside only on the Y chromosome. There are very few Y-linked traits

be XY, resulting in male offspring.

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A pedigree of Y-linked traits

Y-linked traits.

Population GeneticsThe study of gene allele frequency distribution across a population is known as population genetics. This type of study addresses changes in populations, such as adaptation and speciation. The frame work of population genetics, involving the mapping of a set of genotypes to a set of phenotypes is called a genotype-phenotype mapphenotypes, is called a genotype-phenotype map.

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Genotype-phenotype maps can depict changes in phenotype or morphology, even though the genotype is very similar or identical in some cases.



Genetic CounselingGenetic counselors discuss and advise patients about the risk of potential inherited disorders. The likelihood of disease transmission in children and the effects of the inherited disease or disorder are presented.

In the USA, genetic counselors are trained in genetic disease outcomes, possible treatments, and heritability. This education is in addition to their previous biology, psychology or medical background. They

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are certified by the American Board of Genetic Counseling.

Question: Challenge

What is the inheritance pattern of a Y-linked trait?

Males contribute either an X or Y chromosome during fertilization. If an X chromosome is contributed, the genotype

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will be XX female; if a Y is contributed, the genotype will be XY, resulting in male offspring. Y-linked traits appear only in males and are only passed from father to son.



Genetic counselorsdiscuss and

Genetic counselorsdiscuss and

The cell nucleus is usually near the

center of the cell; ithi th l

The cell nucleus is usually near the

center of the cell; ithi th l

RNA is usually single-stranded. It is

made from a DNA blueprint RNA

RNA is usually single-stranded. It is

made from a DNA blueprint RNA

Learning Summary

Y-linked traits appear only Y-linked traits appear only

advise patients about the risk of

potential inherited disorders.

advise patients about the risk of

potential inherited disorders.

within the nucleus, the DNA is

compacted and organized into chromosomes.

within the nucleus, the DNA is

compacted and organized into chromosomes.

blueprint. RNA translates the

message from the DNA to produce the

correct protein.

blueprint. RNA translates the

message from the DNA to produce the

correct protein.

The genetic code dictates The genetic code dictates

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in males and are only passed from father to son. Y-linked genes reside only

on the Y chromosome. There are very few Y-linked

traits.

in males and are only passed from father to son. Y-linked genes reside only

on the Y chromosome. There are very few Y-linked

traits.

gnucleic acid structure and function. The formation of

the end-product amino acids and proteins is controlled by

the genetic code set of rules.

gnucleic acid structure and function. The formation of

the end-product amino acids and proteins is controlled by

the genetic code set of rules.

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Genetics I: Molecular and Human Genetics

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