DNA, genes and chromosomes. Flashcards
DNA in prokaryotes
single, circular chromosomal DNA molecule. - nucleoid
Usually have one or more plasmids.
What are plasmids?
very small circular DNA molecules
contain a few genes
more accessible for protiens required for gene expression and contain genes required often quickly or in emergencies.
genes for antibiotic ressistance are often found in plasmids.
What is the key difference between eukaryotic and prokaryotic DNA?
Prokaryotic does not associate with any protiens.
Eukaryotes have histones.
chromosome structure: draw a chromosome
chromosomes are made of one very long condensed DNA molecule associated with protiens (in eukaryotic cells).
almost an X but it has a circle in the middle to represent the centromere.
the arms are called chromatids.
tell me a little about histones and their role.
they are large +ve globular protiens.
role: organise and condense DNA tightly so that it fits into the nucleus.
what chromatin?
what Chromatids and therefore chromosomes are made of
When does DNA replicate in the cell cycle?
S phase (interphase)
what happens in S phase? Why do sister chromatids need to be identical?
DNA replicates to create two identical strands of DNA called chromatids.
These are joined by a narrow region alled the centromere
these two chromatids are known as ‘sister chromatids’
they are meant to be identical
this is because one chromatid goes into one daughter cell and one goes to the other during mitosis ensuring the daughter cells are genetically identical.
What seals the ends of chromatids?
protective structures called telomeres
Mitocondria DNA
include:
- role of mitocondria
- microscope which can see mitocondria
- structural features
- type of DNA
- role of the DNA
SHORT, CIRCULAR AND NOT ASSOCIATED WITH PROTEINS.
site of aerobic resparation in eukaryotic cells.
just visible in light microscope
surrounded by double membrane
inner membrane folded to form cristae
matrix formed byu cristae contains enzymes needed for aerobic resparation producing ATP
small circular pieces of DNA (mitochondrial DNA) and ribosomes are found in the matrix (needed for replication)
chloroplast DNA
SHORT, CIRCULAR AND NOT ASSOCIATED WITH PROTEINS.
larger than mitochondria DNA
surrounded by double membrane aswell.
membrane bound compartments called thylakoids containing chlorophyll stack to form grana
grana are joined together by lamellae
chloroplasts are the site of light dependent and light independant stages of photosynthesis.
light dependant - thylakoids
light independant - stroma.
also contian circular DNA and ribosomes used to synthesise protiens. needed in chloroplast replication and photosynthesis.
chloroplast DNA
larger than mitochondria
surrounded by double membrane aswell.
membrane bound compartments called thylakoids containing chlorophyll stack to form grana
grana are joined together by lamellae
chloroplasts are the site of light dependent and light independant stages of photosynthesis.
light dependant - thylakoids
light independant - stroma.
also contian circular DNA and ribosomes used to synthesise protiens. needed in chloroplast replication and photosynthesis.
what is a gene?
a base sequence of DNA that codes for the amino acid sequence of a polypeptide or functional RNA molecule
what are functional RNA molecules?
mRNA - the base sequences on messenger RNA molecules are used by ribosomes to form polypeptide chains
tRNA - amino acids are carried to the ribosome by transfer RNA molecules.
rRNA - ribosomal RNA molecules form part of the structure of ribosomes.
what is the initial sequence of amino acids called and what does it change?
primary structure
shape and behavior of the protien molecule.
what do the genes in DNA molecules determine
the exact sequence in which the amino acids join together when protiens are synthesiesed in a cell.
what is a locus?
a fixed position occupied by a gene on a particular DNA molecule.
what is a sequence of 3 DNA bases called and what does it code for?
a triplet
codes for a specific amino acid.
Three characteristics of DNA and explain.
universal
the same genetic code is used in most organisms.
This means the same codons code for the same amino acids in the all living things.
non-overlapping
some of the triplets of bases code for start and stop signals. these tell the cell where individual genes start and stop. This ensures the cell reads the DNA correctly (the code is non-overlapping)
This means that the cell CAN PPRODUCE THE CORRECT SEQUEINCES OF AMINO ACIDS.
degenerate
4 bases 64 total triplets possible
only 20 commonly occuring amino acids in biological protiens.
This means that there are multiple codons coding for the same amino acids which means the code is degenerate.
The what is non-coding DNA
DNA that does not code for any amino acids.
what is an intron?
non-coding DNA within genes.
what is pre-mRNA
the whole gene transcribed. this includes both introns and exons.
what is an exon
a base sequence which codes for amino acid sequences.
what is splicing?
before the pre-mRNA leave sthe nucleus, the non-coding sections (introns) are removed and the coding sections (exons) are joined together. this is splicing.
