chapter 8 - DNA, genes + protein synthesis Flashcards
How does DNA condense into chromosomes ?
- dna molecules are wound around histones ( a type of protein ) to form a dna - histone complex
- theses complexes coil further to create chromatin
- chromatin helps pack the dna into chromosomes
- each chromosomes is molecule of dna wound around histones
What is the dna like in eukaryotes ?
- dna are long, linear dna molecules
- the dna molecules are associated with proteins
- the dna is stored as chromosomes in the nucleus
- dna has introns
What is dna like in prokaryotes ?
- the dna molecules are shorter and circular
- the dna is not associated with histones
- the dna is stored in the cytoplasm
- the dna does not contain introns
- dna is still as chromosomes
What is the DNA like in chloroplasts and mitochondria
- short and circular
- not associated with histones
What is a gene ?
- a short section of dna that codes for a polypeptide and functional rna
What are exons and introns ?
- exons are section of dna that do code for amino acids
- introns are sections of dna that do not code for amino acids
What is a locus
- the specific position along chromosome where a gene is located
What is a genome ?
The complete set of genes within a cell
What is a proteome ?
- the full range of proteins that a cell is capable of producing
What is a triplet code ?
- a sequence of three dna bases that codes for an amino acids
Why is the genetic code universal ?
- because each dna triplet codes for the same amino acid in all organisms
Why is the genetic code non-overlapping ?
- each base in the dna sequence is only read once
- e.g CGTATC
- = CGT and ATC
Why is the genetic code degenerate ?
- because most amino acids is coded for by more than one triplet
What are the features of mRNA ?
- single stranded and linear
- has a base sequence complementary to the dna sequence
- has codons
- is small enough to leave the nucleus
- is made during transcription
What are the features is tRNA
- single stranded molecules folded into a clover leaf shape
- has hydrogen bonds between complementary bases to hold it in shape
- contains a specific sequence of bases at one end which is the anticodon
- has an amino acid binding site on the opposite end
What is the function of mRNA ?
To carry genetic informations from the dna or the ribosomes
What is the function of tRNA ?
- to transport amino acids to ribosomes to build up a polypeptide chain
Describe the process of transcription
- helicase unzips the dna by breaking the hydrogen bonds between the two strands
- rna polymerase binds to dna
- one strand acts a template for mRNA synthesis ( the antisense strand )
- free rna nucleotides align with the dna template, with the bases being complementary to each other
- rna polymerase catalyses the formation of phosphodiester bonds between adjacent rna nucleotides
- when rna a polymerase reaches a stop codon, it leaves
- mRNA leaves an the dna rewinds back into its double helix
What is the difference between transcription in prokaryotes and eukaryotes ?
- in prokaryotes , mRNA is directly produces from transcription without any splicing
- but in eukaryotes both introns and exons are transcribes into mRNA
- this is pre-mRNA which has to go through splicing
- this where the introns are removes and the exons and joined together
- this creates mature mRNA with only exon sequence
- this then travels out of the nucleus for translation
Describe the process to translation
-a ribosome attaches to the mRNA at the start codon
- a tRNA molecules that has a specific amino acid with an anticodon to the start codon binds to the mRNA
- a second tRNA molecule with an anticodon complementary to the mRNA codon attaches to the mRNA
- the amino acids carried by the two tRNA molecules are linked together by a peptide bonds using ATP
- the first tRNA molecules detaches from the mRNA and is free to collect another amino acid
- the ribosome moves along the mRNA which allowed another tRNA with a a specific amino acid to bind to the mRNA
- these steps are repeated until the ribosome meets the stop codon
- then the polypeptide chain detaches from the ribosome
What is an allele ?
- one or a number of alternative forms of a gene
What are the chromosomes like in humans ?
- there are 23 pairs, 46 in total - in each body cell
What area homologous of pairs of chromosomes ?
- a pair of matching chromosomes, they have exactly the same genes as each other , but possibly different alleles
- this is from fertilisation , the sperm gives one chromosome and the egg gives one
- so one from your mother one from your father
