lecture 9: the genome Flashcards
What is the genome and where do we find it?
- Collection (“ome”) of an organism’s DNA
- Found in one or more chromosomes
What is a karyotype?
Used to display the chromosomes of a genome (colors to identify)
Where to find the total genome of an organism?
- Majority of genome = in nucleus —> “nuclear genome”
- But also in mitochondrion and chloroplasts (plants)
What does the genome contain?
- Contains units of information called GENES & informations on HOW to use them
How do we developed from zygote to adult and why do humans are different traits?
Different expression of our genes in a genetic program controls our development from zygote to adult —> giving rise to various specialized cells
- Traits are inherited from parents
- Because of changes in our gene expression —> leads to different traits, even though all humans have same human-like characteristics
Do all cells express all genes?
No: all cells have same genome, but depending on cell type, they only express a SUBSET of the genes in the genome
- They have a unique development program and gene expression pattern
- Depends on function —> specialized for various functions
Do all cells in the body contain the same genes/DNA and the same proteins?
- Virtually yes, because all cells originate form the zygote( fertilized egg)
- Not the same proteome —> depends of function of cells
How does the functions of the cell correlate with its cell structure (3 elements)?
- Cell characteristics (shape)
- Organelle characteristics
- Proteome (collection of proteins)
What are chromosomes made of and what are they?
- Made of chromatin (dynamic structure) and DNA
- Vehicles of heredity
Chromosome structure?
- X-like structure = true definition of chromosome —> only seen during cell division
- Telomere = 4 ends of X
- Centromere = center
- Kinetochore = physical machinery to separate chromosome —> specific region on centromere
What is the haploid number?
Number of chromosomes types in genome (variable n)
- Varies among species
- Higher n ≠ More complex/ larger
What is “ploidy”?
Number of complete sets of chromosomes in genome
- Haploidy (n), DIPLOIDY (2n), Polyploidy
Why do humans have a diploid genome?
Inherit one copy of each chromosome from each parent
What are the 2 types of cells in humans and their ploidy?
- Somatic (body) cells: diploid = 2n = 46 chromosomes
2. Gametes (sex cells): haploid = n = 23 chromosomes
What are two sister chromatids?
2 identical copies of 1 chromosomes —> 1 replicated chromosomes (2 identical chromosomes from 1 parent)
What make two chromosomes “two nonsister chromatids” or “homologous chromosomes”?
- Same length
- Same centromere position
- Same genes at same positions
- Same staining pattern
What are alleles?
Different versions of a gene
- EX: allele that contributes to brown eyes vs allele that contributes to green eyes
- Contribute to different traits
What are the 2 kinds of genotype?
- Heterozygous = 2 different versions of allele
2. Homozygous = same version of allele
What is a genotype?
Combination of alleles that you have
What are autosomal chromosomes (autosomes)?
Non-sex chromosomes
- 22 pairs of autosomes in human genome
What are sex chromosomes (in humans)?
- 1 pair of sex chromosomes in human
- Determine sex using one of many sex-determination systems
- Mammals use XY sex-determination system
- X chromosome = have genes that have nothing to do with sex (because both sex have X chromosome)
- X and Y chromosomes = homologous during cell division even though they have different characteristics
What do genes do? (2)
- Encodes blueprints (directions) to make a specific polypeptide
- Carry information that determines sequences of amino acids in protein & consequently the higher order structure and its function
How does genetic code/ “language” work?
- Analogous to language
- Use the 4 bases (AUCG) to create 61 three-letter codons that are then translated into amino acids
What are gene expression’s 3 transformations and 2 steps?
DNA (gene) —> RNA (mRNA) —> Protein (polypeptide)
- Transcription
- Translation
What are the 3 major players in transcription?
- Gene (template)
- RNA polymerase (enzyme; catalyst that helps to build RNA)
- Ribonucleotides (building blocks) —> AUCG
How does transcription happen?
DNA template strand —> With help of RNA polymerase —> Transcription of RNA from DNA (same language T—>U)
END PRODUCT = a Messenger RNA (mRNA)
How long is a word in the genetic code?
- 3 nucleotides specify a single amino acid
How many kinds of amino acids are used in cells?
20
What consists of the genetic code?
- 64 possible codons with 4 nucleotide types
- 3 nucleotides per codon
- 1 START codon = AUG (Met)
- 3 stop codons
The genetic code is redundant, but not ambiguous. Why?
- Redundant, because multiple codons code for SAME amino acid
- Not ambiguous, because same codons codes are always used in the same ways —> one codon code for one amino aicd
What is the problem when it comes to translate mRNA to a sequence of amino acids, and what is the solution?
- Problem: amino acids do not use complimentary nucleotides —> RNA and polypeptides are different languages
- Solution: use tRNA as ADAPTERS
How does tRNA translate mRNA’s codons to amino acids?
Each tRNA has a specific ANTICODON that can bind to a specific codon —> attached to amino aicd that corresponds to that anticodon
- With help of ribosomes, tRNAs decode 3 nucleotides at a time (1 codon)
Ribosome structure?
Large complex of polypeptides and ribosomal RNAs (rRNA) found free in cytoplasm OR attached to specific organelles
- one large and one small subunit
Ribosome 3 functions?
- Large and small subunits assemble on mRNA and INITIATES translation at AUG start codon
- Provides a site (small space shaped as tRNA) for incoming tRNAS to read appropriate codon
- Catalyzes (accelerates) reaction that forms bond between amino acid on the tRNA and the growing chain of amino acids
What are the 4 major players in translation?
- mRNA (message)
- Ribosome (catalyst)
- Transfer RNAs (tRNA; decoders)
- Amino acids ( building blocks) —> to make polypeptide
How does translation happens?
Ribosome assemble on AUG start codon on mRNA —> tRNA attaches to codons to read message (with anticodon) —> Translate 1 codon at the time to create 1 amino acid —> Ribosome and tRNA moves down the mRNA until stop codon —> Create chain of amino acids
END PRODUCT = polypeptide
Genotype vs Phenotype
Specific genotype contributes to specific phenotype (but also other factors like environment)
- Genotype = combination of alleles
- Phenotype = physical traits that are a product of proteins produced from gene expression (Gene —> mRNA —> Polypeptide)
