ch. 4 genetics and cellular function Flashcards
DNA structure and function
deoxyribonucleic acid (DNA)
long-thread like molcule with uniform diameter, but varied length
* 46 DNA molecules (chromosomes) in nucleus of most human cells
avg human DNA molecule about 2 in long
DNA structure and function
DNA and other nucleic acids are polymers of
nucleotides
* nucleotide consists of a sugar, phosphate group, and nitrogenous base
DNA structure and function
a single nucleotide
- one sugar- deoxyribose
- one phosphate group
- one nitrogenous base
purines-double ring
Adenine (A)
Guanine (G)
pyrimidines-single ring
Cytosine (C)
Thymine (T)
Uracil (U)
DNA bases A, T, C, G
DNA structure and function
double helix shape of DNA (resembles spiral staricase)
- each sidepiece is a backbone of phosphate groups alternating with deoxyribose
- step-like connections between the backbones are pairs of nitrogen bases
DNA structure and function
nitrogenous bases united by hydrogen bonds
- a purine on one strand always bound to a pyrimidine on the other
- A-T two hydrogen bonds
- C-G three hydrogen bonds
DNA structure and function
DNA base pairing
- A-T
- C-G
DNA structure and function
law of complimentary base pairing
one strand determines base sequence of other
DNA structure and function
gene
a segment of DNA coding for the synthesis of a specific protein
DNA structure and function
genome
all the genes of one person
* humans have about 20,000 genes
only about 2% of total DNA
other 98% is noncoding DNA
plays role in chromosome structure regulation of gene activity
chromatin and chromosomes
chromatin
fine filamentous DNA material complexed with proteins
* occurs as 46 chromosomes in most cells
* 6 ft long thread packed in cell nucleus of 5 diameter
* in nondividing cells, chromatin is so slender it cannot be seen with light microscope
* granular appearance under electron microscope
chromatin and chromosomes
histones
proteins crucial for DNA packing
* histones cluster in groups of 8 molecules
* DNA molecule winds around the cluster (like thread around spool)
* chromatin consists of thousands of repeating nuclesomes
chromatin and chromosomes
nucleosome consists of
- core particle–histone cluster with DNA around it
- linker DNA–short segment of DNA connecting core particles
nucleosomes zigzag like an accordian
chromatin and chromosomes
chromatin thrown into
complex, irregular loops and coils
* 1,000 times shorter than original molecule
chromatin and chromosomes
each chromosome is packed into its own region of the
nucleus–chromosome territory
* permeated with channels allowing regulatory chemicals to have access to the genes
chromatin and chromosomes
in a nondividing cell the chromatin is NOT
static
* changes moment to moment according to a genetic activity of cell
* genes get turned off and on
Example: during development, chromosomes migrate, so that
genes on different chromosomes can partner to bring about
developmental changes in the cell
Chromatin and Chromosomes
when preparing to divide cell makes copy of all
nuclear DNA
Chromatin and Chromosomes
each chromosome then consists of 2
parallel filaments of identical DNA–sister chromatids
becomes visible with light microscope
Chromatin and Chromosomes
chromatide are joined at
constricted centomere
* kinetochores–protein plaques on each side of centromere
RNA strucute and function
ribonucleic acids (RNAs)
smaller molecules that resemble DNA
* can have less than 100 or just over 10,000 bases per molecule
RNA strucute and function
3 importanr RNAs for protein synthesis
- messenger RNA (mRNA)
- ribosomal RNA (rRNA)
- transfer RNA (tRNA)
RNA strucute and function
RNA structure
- one nucleotide chain (not a double helix)
- ribose replaces deoxyribose as the sugar
- uracil replaces thymine as a nutrogenous base
- functions mainly in CYTOPLASM
what is a gene?
previous definition of gene
a segment of DNA that carrier the code for a particular protein
* but body has millions of proteins and only about 20,000 genes
What Is a Gene?
Current definition: gene
an information-containing segment
of DNA that codes for the production of a molecule of RNA that plays a role in synthesizing one or more proteins
Amino acid sequence of a protein is determined by the
nucleotide sequence in the DNA
©
What Is a Gene?
Genome
all the DNA in one 23-chromosome set
* 3.1 billion nucleotide pairs in human genome
What Is a Gene?
46 human chromosomes come in two sets of
23
chromosomes
* One set of 23 chromosomes came from each parent
What Is a Gene?
Genomics
study of the whole genome and how its genes
and noncoding DNA interact to affect structure and function
of the whole organism
What Is a Gene?
home sapiens has fewer than
100,000 genes
What Is a Gene?
a single gene can code for many different
proteins
What Is a Gene?
a gene is on avg
3,000 bases long
can be up to 2.4 million bases long
What Is a Gene?
all humans are at least 99.99% genetically
identical
* still 2 individuals can differ by more than 3 million base pairs
* combinations of single-nucleotide polymorphins account for all human genetic variation
what is a gene
some chromosomes are gene ____ and some are gene ____
gene-rich
gene-poor
what is a gene
currentlt we know locations of over 1,400
disease-producing mutation
* opens possibilities of genomic medicine
the genetic code
body can make millions of different proteins (the proteome) from just 20
amino acids and encoded by genes made of just four nucleotides
(A, T, C, G)
the genetic code
genetic code
a system that enables these 4 nucleotides to code for amino acid sequences of all proteins
the genetic code
minimum code to symbolize 20
amino acids is 3 nucleotides per amino acid
the genetic code
base triplet
a sequence of 3 DNA nucleotides that stands for 1 amino acid
the genetic code: base triplet
codon
3-base sequence in mRNA
the genetic code: base triplet
64 possible codons available to represent the 20
amino acids
the genetic code: base triplet
61 code for
amino acids
the genetic code: base triplet
3 codons are
stop codons
the genetic code: base triplet
stop codons
UAG
UGA
UAA
signal “end of message”
like a period at the end of the sentence
the genetic code: base triplet
start codon
AUG codes for methionine
begins the amino acid sequence of the protein
protein synthesis
all body cells except sex cells and some immune cells contain
identical genes
protein synthesis
different genes are activated in
different cells
protein synthesis
any given cells uses 1/3 to 2/3 of its genes
the rest remain dormant and may be functional in other types of cells
