topic 7 - DNA Flashcards
DNA
deoxyribonucleic acid
how does DNA fit into the nucleus
-every human cell has 46 DNA molecules in its nucleus, 23 pairs of chromosomes
- Histones and Chromatin
explain Histones and chromatin
-DNA strands are bound and wrapped around special proteins called histones (looks like a beads on string)
-the “beads on string” then coil up on themselves to form chromatin
histones, chromatin to chromosomes
in cells that are about to undergo cell division (mitosis or meiosis)- the chromatin undergoes further coiling (super-coiled)
-these super coiled structures are called chromosomes
DNA structure - Nucleotide composition
- DNA is polymer
- the repeating units in DNA are called nucleotides
-each nucleotide is made up of a phosphate group, sugar group (deoxyribose) and one of four nitrogenous bases.
name the four nitrogenous bases
Adenine, Thymine, Cytosine, Guanine
DNA structure, double stranded Helix
helix= twisted ladder
sides of ladder:
-sugar phosphate backbone
-the 2 strands run in opposite directions
Rungs of the ladder:
-complementary bases
-A always with T - held together by 2 weak hydrogen bonds
-C always with G - held by 3 hydrogen bonds
importance of bases
-the exact order of A, T, C, G in the DNA determine the genetic code
differences of Nuclear DNA (nDNA) to Mitchondrial DNA
-found in nucleus
-long strands
-Bound to proteins called histones
-46 strands/chromosomes in each nucleus
-thousands of genes
differences of mitochondrial DNA to nucleus DNA
-found in mitochondria
-small, circular strands
-not bound to any proteins
- 5-10 molecules per mitochondrion
- 37 genes:
24 genes for making tRNA molecules
13 genes for making enzymes that involved in cellular respirations
1st step of DNA replication process
step 1- the two strands seperate
-carried out by an enzyme called helicase - unwinds the helix
-made possible due to the weak hydrogen bonds between bases
-each strand will serve as a template for a new complementary strand to be made
2nd step of DNA replication
step 2-make the new complementary strand
-DNA polymerase moves along each of the template strands and makes the new strands
-it obeys the base pair rules
-the 2 new strands are made in opposite directions
define DNA polymerase
an enzyme that joins nucleotides together
role of DNA in a cell
DNA contains the genetic code- order of bases act as the instructions for protein synthesis
explain protein synthesis
-involves joining amino acids together to make proteins
-requires ATP- is an anabolic process
-examples of proteins: hormones, enzyme
how does your cell which amino acids, which order, and how many to use when it makes proteins?
each gene in your genome encodes the instructions for a particular protein
-the DNA within a gene is ‘read’ in sets of 3 (called triplets)
each triplet encodes for a specific amino acid
define ribosomes
ribosomes make proteins
found in cytoplasm
they join the amino acid together to make proteins
give brief explanation of Transcription
-dna is too large and important to leave the nucleus
-cell makes a copy of the gene which encodes the necessary protein
-copy is sent to cytoplasm for ribosomes to ‘read’
-this copy is made out of RNA instead of DNA
-it’s called mRNA (messenger rna)
define Ribonucleic acid
-single stranded
-uses ribose instead of deoxyribose sugar in the sugar phosphate backbone
-uses uracil instead of Thymine
-not as stable-will break down over time
-not good as long term store of the genetic code
define transcription
-the process of making mRNa
-the mRNA copy (which is the copy of the genetic instructions) will later be used by ribosomes to make the encoded protein
-it is smaller than dna and hence can leave the nucleus via the nuclear pores
what does transcription require
RNA polymerase -makes RNA by joining nucleotides together
Helicase- are a subunit of RNA polymerase which unwind and rewind the DNA
nucleotides- A, C, U, G
energy
explain the transcription process:
- initiated by chemical messages:
-enter the nucleus from the cytoplasm
-bind to DNA at start of the relevant gene (region called promotor) - this causes RNA polymerase to also bind to the promotor.
-the helicase parts of the RNA polymerase unwinds the DNA (about 17bp at a time) ahead of the RNA , rewinds it behind. - the RNA polymerase creates an RNA copy of the templates strand.
- when the RNA polymerase reaches the terminator region (special sequence of bases)- it unbinds from the DNA and releases the mRNA transcript
- mRNA then moves into cytoplasm via a nuclear pore
describe the process of translation:
- is the production of a protein using the information coded in the mRNA transcript
- it is carried out by ribosomes
-the ribosome looks for a particular sequence (AUG-start codon) this is where it binds and starts making the protein - the ribosome then moves along the RNA reading it 3bp at a time. Each group of 3bp (called codon) codes for a particular amino acid
translation requirements:
mRNA- the message/copy of the gene- contains instructions for the protein
-ribosome- the protein assembling machine- ribosomes themselves are made out of:
proteins
rRNA- ribosomal RNA- special kind that brings the particular amino acid needed to the ribosome
tRNA- transfer RNA- special kind of RNA that brings the particular amino acid needed to the ribosome
release factors- special proteins that bind to the STOP codons- when the ribosome reaches it will detach from the mRNA and release the protein
tRNA
-responsible for brining the correct amino acid to the ribosome to incorporate into the protein
-are made out of RNA which folds itself into a clover-leaf shape
-two important parts of the tRNA:
amino acid attachment site
Anticodon- a sequence of 3 bases which will correspond to a sequence of 3 bases in the mRNA strand
