BioSci: Genetics

Principles of Genetics, Modes of Inheritance, Genetic Disorders

DNA structure

Deoxyribose sugar phosphate backbone with nitrogenous base pairs

In DNA structure, what sort of links connect 3’ and 5’ hydroxy groups?

Phosphodiester links 3’ and 5’ hydroxyl groups

A DNA nucleotide consists of

a base pair with an attached sugar and phosphate group

Nitrogenous bases are attached to

the ‘1 position of each sugar

Two types of nitrogenous bases are

purines and pyrimidines

Purines include

adenine and guanine (A and G)

Pyrimidines include

thymine and cystine (T and C)

Purines will bind to ______ to link strands

pyrimidines

In DNA, A binds with _____ and G binds with ____

T,C

Structure of DNA is two ____

helical nucleotide chains = double-stranded (diploid)

DNA helices are coiled _____ and contain _____ per complete turn

clockwise around each other, 10 nucleotides

DNA chains run in ____ and are ____ to each other

opposite directions, complementary

In DNA, the bonds holding purine/pyrimidines together are…

hydrogen bonds

Chargaff’s rule tells us that

the ratio of A to T and C to G is 1:1

Human DNA has 3.28 billion base pairs and is 1 m long with ____

21,600 protein-encoding genes (exons)

In DNA, protein-encoding genes typically have …

two copies in human diploid genome

IUbiquitin, a-globulin, and some histone genes have …..

more than gene that codes for them

The majority of DNA is ….

non-coding and repetitive = introns

Repetitive DNA can be in …

tandem (back to back) repeats or be interspersed

There are 3 different sizes of repetitive “satellite” DNA, they are…

micro satellites (<1kb), mini satellites (1-30kb), macro satellites (>30kb)

Short tandem repeats (STRs) can used for

forensic identification of individuals

Repeat numbers on corresponding chromosomes may ____ and is called____

differ, polymorphism

Polymorphisms can be used to

track inheritance of that region of each chromosome (ex. paternity testing)

Function of DNA

Directs protein synthesis and transmission of information from one generation to the nextaE

Each set of 3 DNA base pairs in a row is called a ____ and codes for ___

codon, an amino acid to make protein

During DNA replication…

two strands separate at a number of points to form the replication fork

What structures aid in separating the 2 DNA strands? (3)

1. DNA helices = helps unwind DNA and separates the two strands

2. Topoisomerase = relates the supercoiling that happens during DNA unwinding

3. Single-stranded binding proteins keep the strands separate

Once the DNA strands are separated, the strands will…

serve as a template

New complementary strands are constructed based off the ____ by ______

original DNA strands, DNA-dependent DNA polymerase (DNA pol II)

During DNA replication, free nucleotides are brought in by DNA pol II and will be…

hydrogen-bonded to the template strand

Once bound to the original, separated strands, DNA pol II moves in the _____ direction, which means ______

5’ to 3’, nucleotides are added onto the 3’ end

During DNA replication, primase forms…

short RNA sequences on the DNA (primers) so DNA pol II knows where to attach

Because DNA pol II synthesizes in the 5’ to 3’ direction, replication between the two strands is a little different, resulting in a ____ and a ____

leading strand, lagging strand

Leading strand is….

completed all in one go = continuous

Lagging strand consists of…

Okazaki fragments = DNA pol II synthesizes in fragments then jumps backwards to synthesize the newly separated section (due to the fact that it’s essentially working in the wrong direction due to its directional limitations)

In the synthesis of Okazaki fragments, DNA ligase adds…

free nucleotides to bridge the gaps between each of the fragments

DNA replication is considered to be ____ because ______ of the DNA duplex is conserved in each round, resulting in synthesized strands that are _______

semi-conservative, one strand, half old and half new

DNA replication must be accurate within each ____ and if it isn’t, _____ repair can occur due to ________

cell division, mismatch, DNA polymerase’s “proofreading” function

RNA structure

Ribose sugar phosphate backbone with single nitrogenous bases

RNA nitrogenous bases are …

Purines = A and G

Pyrimidines = U (uracil) and C

RNA is ____-stranded and has _____ polarity

single (haploid), positive

Ribosomal RNAs (rRNAs) are transcribed from

DNA templates within the nucleolus, where they form the core components of ribosomes—structures responsible for protein synthesis

Transfer RNAs (tRNAs) are also synthesized

directly on DNA templates

tRNAs bind to messenger RNAs (mRNAs), which are translated into…

proteins by ribosomes

Some tRNAs being to more than one ___ due to ___

mRNA codon, relaxed base-pairing or “wobble” positions at the third base positions of codons

RNA function is

protein synthesis from transcribed mRNA

DNA codons are used as

templates for mRNA codons

for the DNA sequence “TAC” what will the corresponding RNA sequence be?

“AUG”

Two strands of DNA separate in the area of the gene to be transcribed by…

enzyme helicase

Template strand functions as template for ____ and is read ____ by enzyme ____

mRNA, 3’ to 5’ direction, RNA polymerase II

RNA pol binds to promoter sequence to…

start transcription

mRNA is synthesized in the ____ until ___ is reached

5’ to 3’ direction, transcription terminator

RNA pol adds ___

new nucleotides to 3’ end

During transcription, mRNA is..

processed and modified

During transcription, introns are …

removed because they will not code for a protein; this is done via a post-transcriptional processing called splicing

mRNA splicing is facilitated by

endonucleases

mRNA is further processed and modified to protect it and help export it out of the nucleus; these post-transcriptional modifications include…

1. Addition of a methyl guanylate cap to the 5’ end

2. Addition of a poly-A tail to the 3’ end

Both the 5’ cap and 3’ tail are UTRs, meaning they are …

untranslated regions that will not code for proteins

After post-transcriptional processing, mRNA then ….

diffuses to cytoplasm and DNA strands re-associate via ligase

To begin translation, mRNA codons are sent to

ribosomes to be translated via tRNA into corresponding amino acids

Anticodons are …

complementing sequences on tRNA that bind mRNA codons

A mRNA with an “AUG” codon would bind to what tRNA anticodon?

UAC

During translation, the mRNA strand now looks like..

the RNA version of the original DNA strand

There are ___ possible mRNA codons

64

Each codon will code for one of ___ amino acids

20

Since there are more possible codon combinations than possible amino acids, this is known as ___, meaning that ___

degenerate coding, there will be multiple codon combinations that code for the same amino acid

The start codon is always…

AUG = methionine

Stop codons have 3 possible combinations, which are …

UAA, UGA, and UAG = do not code for an amino acid

In translation, ribosome moves along mRNA from ____ where each codon is recognized by ___

5’ to 3’ end, matching complementary tRNA anticodon

During translation, amino acids are added to

3’ end

tRNA transfers its _____ until stop codon is reached, then ___

amino acid to end of new growing protein chain, it falls off

After translation, ____ occur in the Golgi apparatus

post-translational modifications

Examples of post-translational modifications (8)

• Addition of disulfide bonds = changes shape

• Hydroxylation = adding -OH to it

• Glycolysation = adding carbohydrate for it

• Proteolytic cleavage = chopping it up!

• Phosphorylation = adding PO3 to it

• Acetylation = adding acetyl group to it

• Methylation = adding methyl group to it

• Ubiquitination = adding ubiquitin to it

Post-translational modifications provide newly synthesized proteins with

three-dimensional or tertiary structure

Structure determines how the protein will ___

bind other things and how it functions

If protein structure is disrupted or changed, it will _____

not function well or be non-functional

Only a fraction of genes are _____

expressed in different cells at different times during development

Gene expression and regulation is important for ___

differentiation of cells and tissues

Gene regulation and expression also helps meet fluctuating demands for ___

synthesis of different proteins in each cells during development

Areas of DNA that flank genes are responsible for ____

transcription and synthesis of proteins

Promoter regions before each gene help to

bind RNA pol to the DNA template strand, helps in beginning transcription

The TATA box is a ____

5’ -TATAA -3’ consensus sequence that helps bind transcription factors

Activator transcription factors

initiate transcription of mRNA

Repressor transcription factors

inhibit transcription of mRNA

Transcription is also modulated by ___

enhancers or silencers which can be far away from the promoter region

Enhancers and activators both

start transcription

Silencers and repressors both

inhibit transcription altogether

Silencers, activators, enhancers, or repressors are usually only active in

specific cell types so they regulate tissue specificity of gene expression

__ can occur in gene regulatory sequences, like promoters

Gene mutations

Gene mutations in regulatory proteins like promoters can result in

no gene produced or anomalous patterns of gene expression (ectopic expression)

Large number of specific transcription factors interact with ____ to allow complex patterns of ___; happens in tissue differentiation and physiological receptor signaling

individual enhancers, gene activation

The interaction of many specific transcription factors with individual enhancers to allow complex patterns of gene activation can also happen in

pathological receptor signaling; turned on of off appropriately

80% of genes are only expressed at ____

specific times and places

The remaining 20% of genes are ______

housekeeping genes and expressed in all tissues to fulfill basic metabolic needs

Epigenetics

occurs “above” the genes or changes gene function without changing the actual sequence

Methylation turns off genes usually so____

un-methylated genes are active

Housekeeping genes are ___

unmethylated

Alternative splicing of mRNA lets ____

different gene products be created from one gene (class-switching for antibodies)

Rate of protein translation or degradation also

regulates gene activity

Mutagens induce or increase _____

overall rate of new mutations