UNIT 5: GENETICS

Why do changes in genome occur rapidly, causing disease development?

Short generation times

What characteristics do eukaryote chromosomes have?

Composed of chromatin made up of double stranded DNA and protein. Linear in nature, having more than one.

What characteristics do prokaryote chromosomes have?

Single circular chromosome made up of double stranded DNA with very little protein

In both eukaryotes and prokaryotes, what is the chromosome’s purpose?

Houses information needed for cell function and survival

Deoxyribonucleic acid (DNA)

Nucleic acid made up of nucleotides

Gene

Linear sequence of DNA that codes for one product which is usually a protein

Ribonucleic acid (RNA)

Nucleic acid involved in protein synthesis

True or false. Eukaryotes, prokaryotes, and viruses can have RNA.

True

Genotype

Actual genetic composition of an organism 

Phenotype

Observable traits of an organism due to gene expression

What are the 3 components of nucleotides?

Sugar, phosphate, nitrogen base

Where do phosphodiester bonds form?

Between phosphate molecule and 3’ and 5’ carbons

What is a strand called if it ends with #3 carbon?

3’ end

What is a strand called if it ends with #5 carbon?

5’ end

What does Adenine (A) always bind with and with what kind of bond?

Thymine (T), double hydrogen bond

What does Guanine (G) always bind with and with what kind of bond?

Cytosine (C), triple hydrogen bond

What must a cell do before it can divide?

Make a complete copy of all genetic material

DNA replication

Making a copy of the entire DNA molecule

Why is DNA replication “semi-conservative”?

Each new DNA molecule is made up of one old strand and one new strand

What is the result of DNA replication?

Two identical daughter molecules

DNA unwinds and separates by direction of DNA helicase into two strands. Replication fork at both ends of the segment are used to separate one segment at a time. DNA polymerase matches free nucleotides to base pairs on parent strand. Nucleotides are added in 5’ to 3’ direction. New DNA molecule for 3’5’ orientation template needs special steps to add new nucleotides, resulting in Okazaki fragments that are connected by DNA ligase.

What enzyme unwinds and separates DNA strands during replication?

DNA helicase

What forms at the points where DNA strands separate during replication?

Replication forks at both ends of separated segments

What does DNA polymerase do during DNA replication?

Matches free nucleotides to complementary bases on parent strand

In what direction are new nucleotides added during DNA replication?

5’ to 3’ direction

Why does 3’ to 5’ template strand require special steps during replication?

DNA polymerase can only add in 5’ to 3’ direction. 3’ to 5’ template is copied in short fragments/Okazaki fragments

What enzyme connects Okazaki fragments on lagging strand?

DNA ligase

Why is bacteria DNA replication more difficult?

DNA is single, supercoiled, and circular

Where does DNA replication begin in bacteria?

Origin of replication

Why do two replication forks form during bacterial DNA replication?

Chromosome is circular so replication goes in two directions

How is bacterial chromosome positioned to ensure each new cell gets a copy?

Bacterial chromosome attaches to plasma membrane at one spot

What happens when replication of bacterial chromosome is complete?

Cell elongates, separating the two new chromosomes

What process divides the elongated bacterial cell into two new cells?

Binary fission where cell wall and plasma membrane form to separate the two new daughter cells

What are the 2 major steps for DNA to make protein?

Transcription and translation

What occurs during DNA transcription?

Gene of interest is copied into messenger RNA (mRNA)

Where does DNA transcription take place for each eukaryotic and prokaryotic cell?

Nucleus of eukaryotic cells, cytosol of prokaryotic cells

What occurs during DNA translation?

Genetic information from mRNA is used to synthesize protein

What are the 2 major differences of RNA from DNA?

Nucleotides include sugar ribose not deoxyribose. Can’t bind thymine so it uses urine (U)

True or false. RNA is double stranded in eukaryotes and prokaryotes

False

What is the role of ribosomal RNA (rRNA) and where is it produced?

Structural component of ribosomes consisting of small and large subunits that join in the cytoplasm during translation. Coded by special regions of DNA in nucleoli and contain large amounts of protein

What is the role of messenger RNA (mRNA) and where is it produced?

Carries the codon from DNA to ribosome where it becomes the instructions for production of protein. Produced by copying a gene on DNA as a single stranded RNA.

What is the triplet code?

Every 3 nucleotides in sequence code for one amino acid

What is the role of transfer RNA (tRNA) and where is it produced?

Carries the amino acids to mRNA at the ribosome, matches its nucleotides to mRNA triplet code, and off-loads amino acids to become part of growing protein. Found in cytoplasm.

What is the anticodon?

tRNA triplet code is complementary to mRNA triplet code

What happens first in transcription in prokaryotic cells?

Gene of interest of chromosome is unzipped

What enzyme helps match RNA nucleotides to DNA bases during transcription? 

RNA polymerase

Where does transcription begin and end on a gene?

Begins at the promoter and ends at the terminator

What is the product of transcription?

mRNA

In what direction is mRNA synthesized during transcription? 

5’ to 3’ direction because nucleotides are added to 3’ hydroxyl group on ribose

What happens when transcription is completed?

mRNA and RNA polymerase are released

What happens to mRNA after transcription?

Relocates to ribosome to begin translation

Where does transcription occur in eukaryotic cells?

Nucleus, not the cytoplasm

What is the RNA splicing process for eukaryotic cells during transcription?

mRNA is edited to remove all introns, leaving only exons carrying message to ribosome

Why do eukaryotic cells partake in RNA splicing during transcription?

DNA contains “spacers”/introns that need to be removed so actual coding regions/exons for proteins are left

What is the product of RNA splicing?

Final mRNA

Where does mRNA go after it’s made during transcription?

It moves to a ribosome where small and large subunits join to begin translation

In what direction does the ribosome move along the RNA?

5’ to 3’ direction to read triplet codons

What matches with codons on the mRNA during translation?

tRNA anticodons following base-pairing rules

How are amino acids linked together to form proteins?

tRNA anticodon matches with its codon then its amino acid forms a peptide bond with the previous one forming a growing protein chain

What happens when translation is complete?

Completed protein folds into its functional 3D shape and detaches from ribosome. tRNA returns to cytoplasm to get new amino acids

What is one way to regulate protein synthesis?

Target synthesis of RNA

In prokaryotic cells, how is protein synthesis regulated?

Repression and induction on chromosome at operon sites which regulate gene expression

What is a repressor?

Regulatory protein that blocks the ability of RNA polymerase to bind to a gene and initiate transcription

When does induction occur?

When a particular molecule induces the transcription of a gene

What is a description of an inducer that initiates induction?

A particular product or a product that is induced by the presence of some substance in the cell

Where is lac operon found and what does it do?

It is part of the chromosome in E. coli and it produces enzymes involved in the metabolism of lactose

What does the Lac I region of DNA code for?

An inhibitor (repressor) protein that regulates the lac operon

Where does the Lac I inhibitor bind, and what does it do?

Binds to the operator (O) region and blocks RNA polymerase from binding to the promoter, preventing transcription

What is the function of the Pi region?

Promoter for Lac I inhibitor gene and regulates transcription of the repressor

What happens to the lac operon when no lactose is present?

Repressor binds to operator, blocking RNA polymerase and preventing transcription

What happens to the lac operon when lactose is present?

Lactose binds to the repressor, causing it to detach from the operator, allowing transcription to occur