Mutations

What causes mutations? (3 causes)

1. Errors that occur when DNA is being copied prior to mitosis or meiosis

2. Physical or chemical damage to DNA

3. Errors that occur as chromosomes are being moved during mitosis or meiosis.

deletion mutation

when DNA polymerase sometimes skip one or more bases in the template

insertion mutation

when DNA polymerase inserts one or more extra bases

What is a environmentally induced mutation example?

Thymine dimer is caused when UV wavelengths in sunlight strike a segment of DNA with adjacent thymines in its sequence and because of the amount of energy absorbed it alters the normal phosphodiester bonds between the T nucleotides

What type of mutation is this?

Orginal sequence: A  A  T  G  A  C  C  T  G  G

After mutation: A  T  T  G  A  C  C  T  G  G

Mismatch

What type of mutation is this?

Orginal sequence: A  A  T  G  A  C  C  T  G  G

After mutation: A  A  G  A  C  C  T  G  G

Delection

What type of mutation is this?

Orginal sequence: A  A  T  G  A  C  C  T  G  G

After mutation: A  A  T  G  A  C  C  C  C  T  G  G

Insertion

What types of mutations occur in the structural regions of genes? (4 types)

1. Missense mutations

2. Nonsense mutations

3. Silent mutations

4. Frameshift mutations

What is a missense mutation?

Missense mutations are changes in a single base that lead to a change in both the resulting mRNA codon and the amino acid in the protein product

What is a nonsense mutation?

Nonsense mutations are changes in a single base that change a codon for an amino acid into a stop codon

What results from a nonsense mutation?

translation stops early and the primary sequence of the protein product is only a fraction of its normal length.

What is a silent mutation?

Silent mutations are changes in a single base that lead to a change in the resulting mRNA codon but no change in the resulting amino acid in the protein product

Why do silent mutations occur?

Silent mutations occur because of the redundancy in the genetic code (many different codes can make up the same codon)

What is a frameshift mutation?

Frameshift mutations are changes in one or more bases that lead to a change in the reading frame of codons read by the ribosome during translation.

What results from a frameshift mutation?

frameshift mutations usually change the structure and thus the function of proteins in profound and damaging ways

What is a Deleterious mutation?

Any mutation that decreases fitness; deleterious mutations that lead to early death are termed lethal

What does Gene Expression refer to?

gene expression refers to the entire set of processes that results in using the information stored in a gene

What is Positive control (over gene expression)?

Mechanisms that increase the amount of active gene product available

What is Negative control (over gene expression)?

Mechanisms that decrease the amount of active gene product available.

Structural sequences

contain the information that codes for the amino acids or nucleotides in the final protein or RNA product

Regulatory sequences

are responsible for controlling the rate of transcription or other aspects of gene expression

What is an operon?

A sequence of structural gene sequences whose products have related functions and that are under the control of the same promoter and other regulatory sequences, meaning that they are transcribed as a unit.

What is a promoter?

A promoter is the site where RNA polymerase makes initial contact with DNA to start transcription

What are transcription factors and what do they do?

Transcription factors are regulatory proteins that regulate transcription by binding directly to regulatory sequences in DNA.

What are Activators?

Activators are transcription factors that help exert positive control

What are Repressors?

Repressors are transcription factors that help exert negative control

what are Enhancers?

Enhancers are regulatory sites in DNA that are often involved in positive control

what are Silencers?

Silencers are regulatory sites in DNA that are often involved in negative control

What do Silencers do?

silencers are dna regulatory regions that can decrease gene transcription

What do enchancers do?

Enhancers are DNA regulatory regions that can increase gene transcription

What do activators and repressors do?

Activators and repressors bind specific DNA sequences to increase or decrease gene expression and both can act at the same regulatory region, and their combined activity determines how a gene is expressed

What does positive/negative control depend on?

Positive/Negative control over transcription depends on certain transcription factors binding to certain regulatory sequences in DNA

What is an Exon?

A coding sequence that codes for the amino acids found in a protein product

What is an Intron?

A coding sequence that intervenes between exons and is transcribed but is later removed from the mRNA prior to translation

What are histone proteins?

proteins that have an abundance of positively charged lysines and arginines in their primary structure, which interact with negative charges on the sugar-phosphate backbone of DNA to form nucleosomes. 

What is a chromatin?

The complex of DNA and histones that makes up a chromosome.

how do histone proteins and DNA interact?

Lengths of DNA loop around clusters of eight histone proteins and form nucleosomes. Then nucleosomes get condensed into a compact arrangement, 30-nm fiber

What needs to happen in order for transcription to begin?

Nucleosomes in the condensed state has to change to a decondensed state. This is done by Histone proteins being modified in a way that neutralizes their positive charges

What is a Nucleosome?

A group of four histone proteins that has DNA wrapped around it

What are the steps to transform pre-mRNA to mRNA? (3 steps)

1. Adding the 5′ cap

2. Splicing out introns

3. Adding the poly-A tail

What is a 5’ Cap?

A complex added to the 5′ end of an mRNA that emerges from RNA polymerase during transcription.

What is the 5’ Cap made of?

It is made by enzymes that attach a specially-modified form of the nucleotide guanine along with three phosphate groups

What does the 5’ Cap do? (2 functions)

1. It helps protect the mRNA from RNA-degrading enzymes (which recycle RNAs that are no longer being used by the cell)

2. It helps the mRNA bind to the ribosome so translation can begin

What happens when introns are spliced out?

When Introns are spliced out of the pre-mRNA, a molecular machine (spliceosome) cuts the RNA strand at either end of introns and removes them. Then when splicing is complete, the remaining exons are joined into a continuous strand

Where is a poly-a tail added?

On the 3′ end of a pre-mRNA

How is a poly-a tail added?

a specialized type of RNA polymerase adds a string of dozens to hundreds of the nucleotide adenine

What does a poly-a tail do? (2 functions)

• helps protect the mRNA from RNA-degrading enzymes

• are binding sites for proteins that interact with ribosomes and make translation more likely

once translation results in a completed protein, how can the protein's activity be carefully regulated?

Through Phosphorylation and dephosphorylation which can either activate or deactivate the protein involved

What happens when a protein gets phosphorylated?

a phosphate group forms a covalent bond with a specific R-group on the protein and there will be atoms that have full negative charges

what is a Kinase?

An enzyme that adds a phosphate group to other proteins.