teks b6.a: identify components of dna, and describe how...
TRANSCRIPT
TEKS B6.A: Identify components of DNA, and describe
how information for specifying the traits of an organism is
carried in the DNA.
The components of the DNA are: deoxyribose sugar,
phosphate group, nitrogen base. The three components are
arranged in a molecule called nucleotide. Nucleotides join
together to form the DNA.
The DNA has two sides which are ANTIPARALLEL, which
means they are oriented in opposite direction. The nitrogen
bases are held by HYDROGEN BONDS. In DNA, Adenine
always pairs up with Thymine and Guanine always pairs up with
Cytosine.
The DNA contains the codes to build the structure of
organisms. Each structure corresponds to a part of the DNA
called gene. The one gene one structure hypothesis states
that each kind of protein, each kind of enzyme, and each kind
of hormone in an organism has a corresponding gene in the
organism’s DNA.
The table above shows a comparison of the amount of
nitrogen bases and genes in the DNA of the specified
organisms.
TEKS B6.B: Recognize that components that make up the
genetic code are common to all organisms.
Animals, plants, bacteria and
all other living things have
DNA. Viruses although are not
considered living have DNA
too. The basic components of
the DNA is the same – made up
of the FOUR NUCLEOTIDES,
(A, T, C, G).
From the table above, we can see that the human, mouse, thale
cress, round worm, fruit fly, yeast, bacteria, and virus have
the same group of nitrogen basis in their DNA, they only
differ on the amount and on how they are arranged.
TEKS B6.C: Explain the purpose and process of
transcription and translation using models of DNA and RNA
Gene expression is the process by which genetic codes are
used to create physical structures. The physical structures
are proteins. Gene expression has two steps – transcription
and translation.
Transcription – a strand of the DNA is copied. The copy is
called RNA. It occurs in the nucleus.
Why is transcription important? – The DNA contains the code
to build proteins. Proteins are constructed in the cytoplasm.
DNA cannot get out of the nucleus. To use the DNA code, it
has to be copied into RNA then the RNA goes out of the
nucleus and is used in the construction of proteins.
There are three types of
RNA
a. Messenger RNA or
mRNA – serves as
template in the
assembly of proteins
b. Transfer RNA or
tRNA – serves as
carriers of amino acids
to be assembled as
proteins
c. Ribosomal RNA or
rRNA – combines with
the ribosome that
assembles proteins.
Note:
Ribosome is an organelle that synthesizes proteins.
Amino acids are the building blocks of proteins. There
are 20 different types of amino acids.
Proteins or polypeptides are used as parts to build
many structures in organisms – bone, blood, skin,
muscles, leaves, stems, fruits etc.
Translation – the building of proteins. It occurs in the
cytoplasm.
How are proteins assembled? – each tRNA carry an amino acid.
The tRNAs bring the amino acids to the ribosomes. The
ribosome assembles the amino acids that correspond to the
codes in the mRNA that is being used by the ribosome
starting from the 5’ going through 3’.
Each three letter combination in the mRNA is called
CODON. Each codon corresponds to amino acid.
The three letter combinations in the tRNA that pair with
the codons are called ANTICODONS.
The codon chart shows the corresponding amino acids.
For example:
DNA Codon Anti
codon
Amino acid
CCA GGU CCA Glycine (GLY)
AGT UCA AGU Serine (SER)
CTC GAG CUC Glutamate (GLU)
CAC GUG CAC Valine (VAL)
ATT UAA AUU Stop codon (STOP)
TAC AUG UAC Start codon or Methionine
(MET)
TEKS B6.D: Recognize that gene expression is a regulated
process.
Gene expression is the process by which genetic codes are
used to create proteins. Gene expression has two steps –
transcription and translation.
Gene expression is a regulated process. The DNA contains
nitrogen base sequences that are inchrge of controlling how
the genes are expressed. Some of the controlers may be
affected by environmental factors. This is why gene
expression is affected by the organism’s environment.
Gene regulation can be during:
A. Transcription
B. Translation
C. Post-Translation
TEKS B6.E: Identify and illustrate changes in DNA and
evaluate the significance of these changes
DNA mutation – change in the arrangement of nitrogen
bases in the DNA. The change may be caused by
substitution, insertion, deletion, or frameshift.
Effects of mutation:
1. No effect
2. Harmful effect – like cancer, trisomy, sickle cell
anemia
3. Helpful – resistance to diseases, acquisition of
adaptive traits
Causes of mutation:
1. DNA fails to copy accurately
2. Exposure to some chemicals or radiation
Note:
1. DNA mutation is a natural and common process.
Cells have the ability to repair DNA damages.
In some cases though, damages may not be
repaired completely.
2. DNA mutations in somatic cells affect ONLY
the organism. DNA mutations in gametes are
passed on to and affects even the offspring.
TEKS Recognize the significance of meiosis to sexual
reproduction.
Cells in an organism may be
grouped into two - the
somatic cells and the
gametes or (sex-cells).
Gametes are the sperm and
ovum or egg.
Meiosis is the cell division
by which sperm and egg are
prodcued.
Importance of meiosis:
It allows the creation
of haploid cells making
sexual reproduction
possible.
Note:
Haploid – one set of
chromosomes
Diploid – two sets of
chromosomes
Homologous chromosomes
– chromosomes that have
the same set of genes
but may have different
versions of the genes.
Meiosis is important in sexually reproducing organisms.
During fertilization, a sperm and ovum fuse. Meiosis allows
the formation of haploid cells that will fuse and form diploid
cells during fertilization.
Crossing over during metaphase I allows more genetic
variation or diversity.
Human somatic cells have 46 chromosomes
Human sperm and egg cells have 23 chromosomes
TEKS B6.H: Describe how techniques such as DNA
fingerprinting, genetic modifications and chromosomal
analysis are used to study the genomes of organisms.
DNA fingerprinting is the process of analyzing and
comparing DNA samples. Individual organisms have unique
DNA fingerprint except for identical twins.
Genetic modification or ginetic engineering – the process of
inserting desired genes or removing unwanted genes in an
organism’s DNA. Genes from other organisms can be used like
from one plant to another.
Usually done to improve an organism like making it more
resistant to diseases, to high temperature or to produce
more fruits or grains.
Karyotype shows the number and visual appearnce or position
of chromosomes of an organism. Chromosomal analysis or
karyotype anylysis is the comparison of chromosomal number
and appearnce of a karyotype. It is an important strategy
used to study genetic abnormalities.
As compared to:
The human genome project is the sequencing of proteins in
humans. They identified the nitrogen base sequences in
relation to their functions.
TEKS B6.F: Predict possible outcomes of various genetic
combinations such as monohybrid crosses, dihybrid crosses
and non‐Mendelian inheritance.
Genetics is the branch of biology that deals with heredity.
Research on genetics began with Gregor Mendel, who
experimented on pea plants in the 1800s.
Gene – a segment of DNA that codes for a protein
Allele - alternate form of a gene
Gene for allele
Flower color violet white
Seed shape round wrinkled
Stem size tall short
Mendel’s experiment- crossed pea plants that had different traits:
tall x short purple x white, round x wrinkled seeds
P (Parental Generation) True breeding plants F1 (First Filial) offspring of the P generation --> displayed a single trait F2 (Second Filial) offspring of F1 generation
Allele can be dominant or recessive
Dominant - Allele that is expressed
Recessive - Allele that is hidden
Homozygous - having two of the same allele, true-
breeding or pure breed
AA – homozygous dominant
Aa – homozygous recessive
Heterozygous - two different alleles (Aa); hybrid
Dominant alleles – upper case letters symbol
Recessive alleles – lower case letters symbol
Genotype - the organism’s alleles
Phenotype - the physical appearance
Patterns of Inheritance
1. Law of dominance – recessive trait is covered by
dominant trait
2. Law of codominance – two dominant traits show up in
the organism/s phenotype at the same time
3. Law of incomplete dominance – two traits that are not
dominant will produce a third phenotype, a blending of
the two traits
4. Law of segregation – the alleles of a gene segregate
during gamete (sperm or egg) formation
5. Law of independent assortment - each pair of allele
segregates independently of other pairs of alleles
6. Sex-linked traits – some genes are located on the X or
Y chromosome and they always go with being a male or
female
7. Traits with multiple alleles – a trait is controlled by
more than two alleles
8. Polygenic Traits – traits are controlled by groups of
several genes
9. Pleiotropy – a gene affects more than one unrelated
traits
Crosses and genotype and phenotype probability
Monohybrid cross – cross involving only one trait
Dihybrid cross – cross involving two traits
Genotype ratio: Phenotype ratio: YY – 0 yellow – 4 Yy – 4 green – 0 yy – 0
4:0:0 4:0
Yellow – 100 % Green – 0%
Homozygous – 0% Heterozygous – 100%
Phenotype ratio: Yellow and round – 16 Yellow and wrinkled - 0 Green and round – 0 Green and wrinkled – 0
16 : 0 : 0 : 0 Yellow and round – 100% Yellow and wrinkled – 0% Green and round – 0% Green and wrinkled – 0%