Topic 4 — A: DNA, RNA and Protein Synthesis Flashcards
How is DNA stored?
- structure of DNA is the same in all organisms, but organisms, eukaryotic and prokaryotic cells store DNA in slightly different ways.
DNA of Eukaryotic cells:
contain linear DNA molecules that exist as chromosomes — thread-like structures, each made up of one long molecule of DNA and
its associated proteins.
- Chromosomes are found in the nucleus.
shape of DNA molecules in eukaryotic cells:
long, so it has to be wound up so it can
fit into the nucleus. It’s wound around proteins called histones.
what do Histone proteins do?
help to support the DNA.
The DNA (and protein) is then coiled up very tightly to make a compact chromosome.
DNA in mitochondria and chloroplasts:
have their own DNA.
- similar to prokaryotic DNA but circular and shorter than DNA molecules in the nucleus + not associated with histone proteins.
Prokaryotic cells DNA:
- carry DNA as chromosomes
- but the DNA molecules are shorter and circular. The DNA isn’t wound around histones — it condenses to fit in the cell by supercoiling.
process of DNA coiling:
DNA double helix → circular chromosome → coiled chromosome → super coiled to fit in cell
how much of DNA carries genetic info?
Only a small amount of the DNA in a cell carries genetic information.
The most important parts of a DNA molecule are the genes.
what does DNA contain?
genes
what is a gene?
sequence of DNA bases that codes for either a polypeptide or functional RNA
- The sequence of amino acids in a polypeptide forms the primary structure of a protein
what do Different polypeptides have?
a different number and order of amino acids.
what does the order of bases in a gene determine?
the order of amino acids in a particular polypeptide
what is Each amino acid is coded by?
a sequence of three bases in a gene called a triplet or codon
making a polypeptide (first stage of protein synthesis)
DNA is first copied into messenger RNA (mRNA).
what do Genes that don’t code for a polypeptide code for?
functional RNA
what is Functional RNA?
RNA molecules other than mRNA, which perform special tasks during protein synthesis, e.g. tRNA and ribosomal RNA (rRNA), which forms part of ribosomes.
genome definition:
The complete set of genes in a cell
what is a proteome?
full range of proteins that the cell is able to produce
what does nuclear DNA in eukaryotes NOT code for?
doesn’t
p code for polypeptides
what do genes that do code for polypeptides also contain?
sections that don’t code for amino acids (introns)
introns within a gene:
There can be several introns within a gene and their purpose isn’t known for sure.
how are Introns in eukaryotes removed?
protein synthesis — so they don’t affect the
amino acid order.
does Prokaryotic DNA have introns?
no
exons meaning:
All the bits of a gene that do code for amino acids