PKU, DNA Packaging, Chromosomal Genetics, and Mitosis Flashcards
What is phenylketonuria (PKU)? What causes the disease and how can it be treated or prevented? Why is genetic testing at birth so important for identifying PKU early?
PKU is a human disorder associated with delayed mental and social skills, seizures, rashes, and pale skin/hair/eyes
PKU is caused by the lack of functional PAH enzyme, which allows for a buildup of excess phenylalanine- causing disease
It is treated/prevented with a special diet of foods low in phenylalanine
Genetic testing is vital as the disorder can be caught early enough to put the diet in place and prevent progression in the child
What is phenylalanine hydroxylase (PAH)? What type of macromoleclue is it and what does it do in the cell? In individuals lacking active PAH, how does dysfunction lead to PKU?
PAH is a cellular enzyme responsible for converting excess phenylalanine into tyrosine
PAH is a protein
Conversion of phenylalanine into tyrosine is important for sythesis of melanin and neurologically important chemicals for development and stability.
What is an enzyme? What type of macromolecule is it? Be able to identify and describe the imporance of enzymatic substatres and active sites. What is the substrate and product of the enzyme PAH?
Am enzyme is a protein that functions as a catalyst to speed up chemical reactions w/o being directly changed in the reaction.
The substrate is the chemical reactant that binds specifically to the enzyme and he active site is where the substrate binds to the enzyme
PAH substrate- phenylalanine; product- tyrosine
How many chromosomes comprise the human genome? What are autosomal chromosomes and how many does a typical human have? What are sex chromosomes? Where is the gene locus (chromosome number) for PAH and what type of chromosome is it on?
46; 23 pairs of chromosomes
autosomal chromosomes cotain non-sex genes (22/23 pairs)
Sex chromosomes are the single pair that codes for biological sex and secondary sex characteristics
PAH is on the 12th autosomal chromosome in the locus 12q22-q24
Give a quick overview of how a gene is used to produce a protein.
DNA nucleotides from each gene are transcribed into RNA; the RNA is modified to remove non-coding regions to create mRNA, which is then used as a template to be translated into a protein by enzymes called ribosomes.
What is a mutation? How do mutations disrupt protein structure? Where is the original mutation responsible for disease located (in the DNA, RNA, or protein)?
Mutation- an accidental change in genetic material
They can disrupt protein structure due to the incorrect protein being created, thus the protein is unable to fold properly b/c may be missing a critical bond location.
Mutations are located in the DNA
What are alleles? What is meant by the terms “genotype” and “phenotype”
Alleles- the two analogous copies of the same gene
Genotype- the genetic makeup of one or more genes
Phenotype- the observed physical effects of a certain genotype or allele
What type of disease is PKU (autosomal or sex-linked / dominant or recessive)? What is meant by the term carrier? Be able to describe how two parents which do not have PKU may have a child with the disease.
PKU is an autosomal recessive disease
Carrier- a person who carries, but does not present with, the the recessive gene for a disease
If neither parent is a carrier, the child can still get PKU through an independent genetic mutation.
What are the three domains of life? Which are considered prokaryotes and eukaryotes? What are the characteristics of prokaryotic and eukaryotic cells?
Bacteria, Archaea, Eukarya
Bacteria and Archaea are prokaryotes; Eukarya are eukaryotes
Prokaryotes are unicellular and have no nucleaus or organelles; eukaryotes can be uni- or multicellular and they have nuclei and membrane-bound organelles
Where is the genomic DNA of prokaryotes found in a prokaryotic cell? What are plasmids and where are they found? Are plasmids considered part of the bacterial genome? Why or why not?
Prokaryotic DNA is free-floating w/in the cell
Plasmids are additional, non-necessary pieces or DNA which can code for survival advantages
Because they are non-necessary, they are not considered part of the genome
Where is the genomic DNA of eukaryotes found in a eukaryotic cell? Where else in a eukaryotic cell might DNA be found? What are the functions of mitochondria and chloroplasts?
Eukaryotic DNA is tightly packed w/in the nucleus of the cell, and can also be found in the mitochondria and chloroplasts, which are used for energy generation
What is the primary problem with storing DNA in prokaryotic and eukaryotic cells?
How to store all of the DNA: for example, the DNA of one human cell is 7 feet long and it to be packed into a space smaller than the eye can see, but still be accessible for use
How do prokaryotes package their genomic DNA? What is supercoiling? What are the two types of supercoiling and how is each created?
Prokaryotes package their DNA via supercoiling- the over or under-winding of a DNA strand due to applied strain
Positive supercoiling- overrotation
Negative supercoiling- underrotation
What type of enzyme is responsible for relieving strain in DNA? How do topoisomerases work?
Topoisomerase is the enzyme that cuts, rotates, and reattaches the DNA strands to relieve pressure
In general terms, how do eukaryotes package their DNA? What is chromatin? What is a chromosome?
Eukaryotic DNA binds with scaffolding proteins called histones to form a tightly wound structure called a chromosome
What are histones? Why are they positively charged and how does the positive charge help in packaging DNA?
Histones are small positively-charged scaffolding proteins
They are positively charged due to the basic amino acids coating their surface
DNA is negatively charged, so they bond easily
What is a nucleosome? During DNA packaging, by what name is the first step often given? How does DNA wrap around the histone complexes to form these “beads”?
Nucleosome- DNA wrapped twice around a group of histones, forming “beads on a string”
Which histone protein is responsible for forming the 30-nm fiber? How many nucleosomes form a single coiled turn of the 30-nm fiber?
The H1 histones interact w/ one another to pull the “beads” into a thicker structure
6 nucleosomes wrap around to form one turn of the 30nm fiber
What are looped domains? What is the diameter of the DNA at this stage of packaging
looped domains- when the 30 nm fiber binds to a non-histone protein scaffold and forms loops
diameter- 300 nm
The last step of DNA packaging involves forming a 700-nm compacted chromosome structure. Why does the diameter double leading up to cell division?
The diameter doubles because the chromosome has to duplicate into a pair of sister chromatids
What is the difference between euchromatin and heterochromatin? Which is more likely to be used for actively expressed genes? Which stages of packaging are euchromatin and heterochromatin often found? What is meant by the term epigenetics?
Euchromatin contained actively expressed genes, so it remains less tightly packed so that it can be read; often found in 10 or 30 nm form
Heterochromatin contains mostly inactive genes and stays tightly packed; often found in 300 nm or sometimes 30 nm form
Epigenetics- the study of the mechanisms for regulating gene activity independent of sequence, the basis of stem cell research
What is a gene?
A discreet unit of heredity made of a specific sequence of DNA which contains the genetic information for a particular trait
What type of genomic chromosome organization (e.g. shape, number of chromosomes) do eukaryotes generally have? Prokaryotes?
Eukaryotic chromosomes are generally linear, and there are several chromosomes
Prokaryotic generally have 1 circular chromosomes
What are homologous chromosomes?
Chromosomes that pair during meiosis- code for the same sets of genes but are not identical
What are heterologous chromosomes?
Chromosomes that do not pair during meiosis and do not code for the same sets of genes
What is meant by the terms homozygous alleles and heterozygous alleles? What is the significance of having homozygous or heterozygous alleles in regards to a phenotype?
Homozygous alleles have the same gene sequence- AA
Heterozygous alleles have different sequences- Aa
The significance is that a buffer of sorts is formed against recessive mutation
What are some primary reasons for cells to undergo cell replication? What are the goals of cell division? What are the three primary types of cell division?
Goals: Copying the genomic material, separate the copies of genomic material, split the cell into two/ reproduction
Types: binary fission, mitosis, meiosis
During the eukaryotic cell cycle, what are the two main stages? What happens during interphase and mitosis?
Interphase and the Mitotic phase
Interphase- non dividing phase of the cell cycle, consists of normal cell activities and division prep such as genome duplication
Mitosis- dividing phase, results in two daughter cells
What are the three main phases of interphase? What is the G0 phase? What is the purpose to checkpoints between interphase phases?
G1, S, and G2
The G0 phase is the “resting phae of the cell, allowing the cell to stay in G1 for as long as necessary
G1 checkpoint- ensures there is no DNA damage and all the enzymes necessary for DNA synthesis are present
G2 checkpoint- ensures the DNA had been copied successfully and has no damage
What is meant by the terms haploid and diploid?
Haploid- only have one copy of each chromosome; gametic cells
Diploid- have two homologous copies of each chromosome; somatic cells
What are sporophytes and gametophytes? Which is diploid and haploid? Which type of division produces the spores? Are spores considered diploid or haploid?
Sporophyte- a diploid (2n) plant organism derived from fertilization
Gametophyte- a haploid (1n) plant organism derived from spores
Spores are usually haploid
What is a zygote?
A diploid (2n) cell formed by the fusion of two gametes- sexual reproduction
