DNA Flashcards
What is the structure of DNA
-nucleotides
-deoxyribose (sugar) and a phosphate backbone
-weak hydrogen bonds between bases
-nitrog. bases: cytosine, thymine, guanine, adenine
-make two chains that twist into a spiral shape known as a double helix
-DNA strands wrap around special proteins called histones to form nucleosome which later are known as chromatin or chromosome depending on the cells dividing properties
found in cell nucleus and mitochondria
What is a chromatin?
Tangled network formed from coiled DNA
What makes up chromosomes? How many are in a somatic cell?
46
-made up of tightly coiled chromatin that go through cell division
What is the difference between mitochondrial DNA and nuclear DNA?
Mitochondrial:
-small circular molecules
-not bound by proteins
Nuclear
-long double helix structure
-bound by proteins(histones)
What is a nucleosome made of?
DNA wrapped around eight histone proteins
What are some similarities between transcription and DNA replication
-occur in the nucleus
-rely on enzymes in order to occur
-make complementary strands using nucleotides A, C, G, and T or U
-DNA is used as a template
-The new strand is synthesized 5’-3’
What is translation?
the production of a protein using the information that is coded in the mRNA molecule
How does translation occur?
-in the cytoplasm
-a ribosome, along with tRNA, attaches to one end of the mRNA molecules
-tRNA’s and ribosomes then move along mRNA 3 bases at a time (codon), reading them as it goes
-when tRNA, carrying corresponding anticodons to the mRNA’s codons, and ribosome reaches the starting codon, it translates that genetic code into a specified string of amino acids
-folds to form protein
What is transcription?
The process by which the mRNA is formed using the code in a DNA molecule
How does transcription occur?
-the DNA’s genetic instruction are replicated or transcribed to the mRNA molecule
-the enzyme RNA polymerase make double sided DNA strand come apart
-RNA polymerase then transcribe bases of one strand=complementary mRNA molecule
-at the end of gene-sequence of bases that tell RNA polymerase to stop copying=mRNA molecule release
-the introns are removed leaving the exons
-the functional mRNA will leave nucleus and direct protein synthesis in the cytoplasm
How does protein formation occur?
transcription and translation
What is a gene?
An inherited strait factor that codes for a specific protein
What is an allele?
Alternative form of a gene
Define dominant
An allele that masks the effect of another allele
e.g. A and B or I
Define recessive
Allele that is masked by the alternative, dominant allele
e.g. 0 and i
Define homozygous
The situation where an individual has the same alleles for a particular characteristic i.e. pure breeding
Define heterozygous
The situation where an individual possesses different alleles for a particular characteristic i.e. hybrid
Define phenotype
The physical appearance of an individual as determined by the expression of the alleles for that characteristic
Define genotype
The genetic make-up of an individual as determined by the alleles for the characteristic being considered
Define Punnett square
Means of calculating the probability of genotypes and phenotypes of offspring
Define pedigree
Family tree/register recording a line of ancestors
What is RNA’s structure?
-made up of nucleotides, which are ribose sugars attached to nitrogenous bases and phosphate groups
- nitrogenous bases include adenine and uracil as well as , guanine, uracil, and cytosine
Causes of variation
- crossing over
- non-disjunction
- random/independent assortment
- random fertilisation
What occurs during ‘crossing over’?
Occurs in meiosis
Legs of homologous chromosome become tangled and DNA is exchanged increasing genetic variety
e.g. brothers and sisters having differing traits
What occurs during non-disjunction?
Occurs during meiosis
Chromosome pairs do not separate properly resulting in gametes receiving an additional chromosome/none of a pair at all
e.g. down syndrome, turners, Klinefelter’s
What occurs during random/independent assortment?
Chromosomes are independently assorted into gametes during meiosis
Homologous chromosome pairs are split up to ensure each gamete has ‘n’ set of chromosomes and migrate to poles of cell
What occurs during random fertilisation?
-does not occurs in meiosis but happens following cross over and independent chromosome assortment
-during fertilisation
-final process that increase variation through random sperm fertilising a random ovum
What is co-dominance?
When contrasting alleles both affect the appearance of an individual and neither is dominant over the other i.e. neither is masked
e.g. A and B or Ia and Ib
What is epigenetics?
study of phenotypic expression of genes
altering the functioning of existing DNA by turning on or off the genes within
-there are flags which enhance/silence gene expression
-methyl groups silence gene expression/stop protein being made
.associated with CpG regions (alternating CGCGCG)
-acetyl groups promote gene expression
.associated with histone modification
Function of helicase
Enzymes responsible for the separation of DNA strands during replication
Function of DNA polymerase
Enzyme that joins nucleotides together
Function of RNA polymerase
Enzyme that is active during transcription of RNA from DNA-copies the sequence
Function of primase
synthesizes short RNA sequences called primers
primers serve as a starting point for DNA synthesis
What is autosomal inheritance?
a specific gene that is not on a sex chromosome and is a numbered chromosome
inherited
-trait is independent of the individuals sex
What is sex-linked inheritance?
x linked
-all offspring may inherit trait
-male offspring will definitely express trait
-females have 2 x chromosomes so may not
y linked
-only effects male lineage
-because they carry two different sex chromosomes
-alleles are hemizygous
How is dominance proven?
-two parents have/express trait
-one or more offspring are different
-parents are dominant for trait and carriers of recessive allele
How is recessiveness proven?
DNA function
Stores the information for the production of proteins that determines the structure and function of cells
What is acetylation?
addition of an acetyl group to a histone protein so that gene expression is enhanced
What is methylation?
addition of a methyl group to a DNA molecule resulting in inhibition of gene expression
What is mono hybrid cross?
a cross between two organisms with different variations at one genetic locus of interest.
What is tRNA?
Transfer RNA
-molecule that brings amino acids from cytoplasm to ribosome
-each tRNA has an anti-codon which matches to the corresponding codon on mRNA
-anticodon corresponds to a specific amino acid
What is mRNA?
Messenger RNA
-molecule that transfers coded information from nucleus, through cytoplasm, to the ribosomes
What is rRNA?
Ribosomal RNA
-Nucleic acids that form part of the ribosomes
Why is only maternal DNA used in studies of ancestry?
MtDNA
At fertilisation the mitochondrial DNA is destroyed. Only the DNA in the ovum is maintained thus it can be used in ancestry studies.
Relationship between lipid synthesis and DNA
Indirect relationship
-DNA encodes for the synthesis of proteins which are enzyme involved in the synthesis of lipids
-DNA does not directly encode for lipid synthesis
Define epigenome
Layer of chemical tags that cover genome-effected by environmental conditions
