DNA, genes, chromosome Flashcards
What is a gene
A section of DNA that contains the coded information for making polypeptides and functional RNA
Loci
section of DNA located at a particular position
What does a gene code for
amino acid sequence of polypeptide, functional RNA, rRNA, tRNA
Only ___ different amino acids regularly occur in proteins
20
What are the main features of genetic code?
degenerate as multiple codons code for the same amino acid. The code is non-overlapping - each base is only read once. the code is universal - each triplet codes for the same amino acid in all organisms
What are non-coding sequences made out of?
Between genes, there are non-coding sequences made up of multiple repeats of base sequences.
Exons are separated by
non-coding sequences called introns
DNA and chromosomes:
Differences between eukaryotic and prokaryotic cells -> Pro: DNA molecules shorter, circular and not associated with histone
Chromosomes structure:
Chromosomes appear as 2 threads joined at a single point -> each thread is called a chromatid (because DNA has already replicated to give 2 identical DNA molecules)
Formation of chromosome:
DNA + histones -> DNA histone complex -> coiled -> further coiled and packaged into chromosome
Homologous chromosomes:
two chromosomes that carry the same genes but not necessarily the same alleles of the genes
Why are homologous chromosomes important?
Each pair is derived from chromosomes provided by egg and sperm
What happens during meiosis to the chromosomes?
Halves the number of chromosomes in a way that ensure that each daughter cell receives one chromosomes from each homologous pair.
What is allele?
One of a number of alternative forms of a gene
How are alleles structurally different from each other?
Allele has a different base sequences, therefore a different amino acid sequence, so produces a different polypeptide
What happens when a mutation occurs?
Any changes in the base sequence of a gene produces a new allele of that gene
What is a codon?
three bases on mRNA that codes for a single amino acid
What is a genome?
the complete set of genes in a cell
Proteome -
- full range of proteins produces by the genome
What is the structure of RNA?
Polymer up a repeating mononucleotide sub units, made out of: Ribose, AUGC - bases, phosphate group
mRNA structure:
single stranded linear, removed introns
Function of mRNA:
acts as a template for protein synthesis, form codons which determine amino acid sequence.
tRNA structure:
relatively small molecule, single stranded folded into cloverleaf shape, anti-codon complementary to codon
What occurs in transcription?
> DNA unwinds to expose the bases to act as a template
only one chain of DNA acts as a template Unwinding and unzipping is done by DNA Helicase - which breaks the hydrogen bonds between bases
Free RNA nucleotides in nucleus align opposite exposed complimentary DNA bases
The enzyme RNA polymerase joins together the RNA nucleotide to create new RNA polymer chain.
Splicing occurs to remove introns
