3.4.1 DNA, Genes + Chromosomes Flashcards
How many chromosomes do humans have
46 chromosomes (23 pairs)
What are DNA molecules like in prokaryotic cells
Short,circular and not associated with proteins
What are DNA molecules like in the nucleus of eukaryotic cells
Very long,linear and associated with histone proteins
What proteins are dna molecule sin a eukaryote associated with
Histones
What does a dna molecule and its associated proteins form
A chromosome
In eukaryotic cells, what other 2 organelles contain dna
What’s it like
Mitochondria + chloroplasts
Short,circular and not associated with proteins (like prokaryotic dna)
What are homologous chromosomes
Chromosome pairs where each chromosome is alike and have genes for the same characteristic at corresponding loci (positions)
What are alleles
Genes which occur at the same position (loci) on a pair of homologous chromosomes
What’s a gene
What does it code for
A short length of dna that codes for :
- amino acid sequence of a polypeptide
- a functional RNA (including ribosomal RNA + tRNAs)
What does a gene occupy on a particular dna molecule
A fixed position called a locus
What does each triplet on a gene code for
Amino acid
What does the degenerate code mean
Some amino acids have more than 1 codon
What does it mean when the code is non-overlapping
Each base is part of 1 codon sequence of triplets/bases that code for a protein
What does it mean if the code is universal
3 base triplets code for amino acid in every species +cell from simple to complex
How many codons code for 20 amino acids
64
Why is the genetic code degenerate
As many amino acids can be coded for by several different codons (64 codons code for 20 amino acids)
What’s the genome
Complete set of genes in a cell
What’s the proteome
Full range of proteins a cell can produce
What’s RNA
A nucleic acid like DNA but with differences
4 differences RNA has to DNA
- has ribose sugar instead of deoxyribose
- has the base uracil instead of thymine
- usually single stranded
- usually shorter than dna
What can rna do like proteins
Fold into 3D
What does mRNA do
Carries the message that codes for a particular proteins from the nucleus (where DNA master copy is) to the cytoplasm (where proteins are synthesised in ribosomes)
What’s mRNA like
Single stranded
Just long enough to contain 1 gene only
What happens to mRNA shortly after it’s used
It’s degraded - has a short lifetime
Why would a cell have a higher concentration of mRNA
If it’s doing more protein synthesis
What does rRNA with proteins form
Ribosomes
What’s rRNA
Ribosomal rna
What are ribosomes the site of
mRNA translation and protein synthesis
What are ribosomes made up of
2 subunits, small and large
What’s rRNA codes for by
Numerous genes in many different chromosomes
What 2 places are ribosomes
Cytoplasm
RER
What do free ribosomes in the cytoplasm make protein for
Cell use
What do ribosomes attached to the RER make proteins for
Export
Describe the genetic code (3)
Universal
Non-overlapping
Degenerate
What’s a triplet
Sequence of 3 DNA bases
Within a gene what the sequences that actually code for amino acid sequences called
Exons
What are exons separated by within the gene
One/more non-coding sequences called introns
